{{Short description|Infection that develops from a pre-existing condition}} {{Infobox medical condition | name = Opportunistic infection | synonyms = | image = Chest X-ray in influenza and Haemophilus influenzae - annotated.jpg | caption = Chest X-ray of a patient who first had influenza and then developed ''Haemophilus influenzae'' pneumonia, presumably opportunistic | pronounce = | field = | symptoms = | complications = | onset = | duration = | types = | causes = | risks = | diagnosis = | differential = | prevention = | treatment = | medication = | prognosis = | frequency = | deaths = }} An '''opportunistic infection''' is an infection that occurs most commonly in individuals with an immunodeficiency disorder and acts more severely on those with a weakened immune system. These types of infections are considered serious and can be caused by a variety of pathogens including viruses, bacteria, fungi, and parasites.<ref name=":03">{{Cite web |title=What is an Opportunistic Infection? {{!}} NIH |url=https://hivinfo.nih.gov/understanding-hiv/fact-sheets/what-opportunistic-infection#:~:text=What%20is%20an%20opportunistic%20infection?%20Opportunistic%20infections%20(OIs),weakened%20immune%20systems%20include%20people%20living%20with%20HIV. |access-date=2025-02-26 |website=hivinfo.nih.gov |language=en}}</ref> Under normal conditions, such as in humans with uncompromised immune systems, an opportunistic infection would be less likely to cause significant harm and would typically result in a mild infection or no effect at all. These opportunistic infections can stem from a variety of sources, such as a weakened immune system (caused by human immunodeficiency virus and acquired immunodeficiency syndrome), when being treated with immunosuppressive drugs (as in cancer treatment),<ref name=":122">{{cite book |title=StatPearls |vauthors=Justiz Vaillant AA, Qurie A |date=2021 |publisher=StatPearls Publishing |place=Treasure Island (FL) |chapter=Immunodeficiency |pmid=29763203 |access-date=2021-03-09 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK500027/}}</ref> when a microbiome is altered (such as a disruption in gut microbiota), or when integumentary barriers are breached (as in penetrating trauma). Opportunistic infections can contribute to antimicrobial resistance in an individual making these infections more severe. Some pathogens that cause these infections possess intrinsic resistance (natural resistance) to many antibiotics while others acquire resistance over time through mutations or horizontal gene transfer.<ref>{{Cite journal |last=Sánchez |first=María Blanca |date=2015-06-30 |title=Antibiotic resistance in the opportunistic pathogen Stenotrophomonas maltophilia |journal=Frontiers in Microbiology |language=English |volume=6 |page=658 |doi=10.3389/fmicb.2015.00658 |doi-access=free |pmid=26175724 |pmc=4485184 |issn=1664-302X}}</ref> Many of these pathogens, such as the bacterium ''Clostridioides difficile (C. diff),'' can be present in hosts with uncompromised immune systems without generating any symptoms, and can, in some cases, act as commensals until the balance of the immune system is disrupted.<ref>{{Citation |last1=Mada |first1=Pradeep Kumar |title=Clostridioides difficile infection |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK431054/ |access-date=2025-01-30 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=28613708 |last2=Alam |first2=Mohammed U.}}</ref><ref>{{Citation |title=Clostridioides difficile |date=2025-01-15 |work=Wikipedia |url=https://en.wikipedia.org/wiki/Clostridioides_difficile |access-date=2025-01-30 |language=en}}</ref><ref name=":2">{{cite journal | vauthors = Schroeder MR, Stephens DS | title = Macrolide Resistance in ''Streptococcus pneumoniae'' | journal = Frontiers in Cellular and Infection Microbiology | volume = 6 | page = 98 | date = 2016-09-21 | pmid = 27709102 | pmc = 5030221 | doi = 10.3389/fcimb.2016.00098 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Achermann Y, Goldstein EJ, Coenye T, Shirtliff ME | title = Propionibacterium acnes: from commensal to opportunistic biofilm-associated implant pathogen | journal = Clinical Microbiology Reviews | volume = 27 | issue = 3 | pages = 419–40 | date = July 2014 | pmid = 24982315 | pmc = 4135900 | doi = 10.1128/CMR.00092-13 }}</ref> With ''C. diff'' and many other pathogens, the overuse or misuse of antibiotics can cause the disruption of normal microbiota and lead to an opportunistic infection caused by antibiotic resistant pathogens.<ref>{{Cite journal |last1=Raplee |first1=Isaac |last2=Walker |first2=Lacey |last3=Xu |first3=Lei |last4=Surathu |first4=Anil |last5=Chockalingam |first5=Ashok |last6=Stewart |first6=Sharron |last7=Han |first7=Xiaomei |last8=Rouse |first8=Rodney |last9=Li |first9=Zhihua |date=2021-02-15 |title=Emergence of nosocomial associated opportunistic pathogens in the gut microbiome after antibiotic treatment |journal=Antimicrobial Resistance & Infection Control |volume=10 |issue=1 |page=36 |doi=10.1186/s13756-021-00903-0 |doi-access=free |issn=2047-2994 |pmc=7885457 |pmid=33588951}}</ref> In some cases, opportunistic infections can be labeled as a hospital-acquired infection due to individuals contracting them within a healthcare/hospital setting.<ref>{{Cite web |date=2021-08-20 |title=Opportunistic pathogen - Definition and Examples - Biology Online Dictionary |url=https://www.biologyonline.com/dictionary/opportunistic-pathogen |access-date=2025-02-26 |website=Biology Articles, Tutorials & Dictionary Online |language=en-US}}</ref> In terms of history, there is not one individual that can be attributed for discovering opportunistic infections. Over time and through medical advancement, there have been many scientists that have contributed to the study and treatment options for patients affected by these infections.<ref>{{Cite web |date=2009-06-18 |title=Study takes aim at opportunistic fungal pathogens |url=https://news.mit.edu/2009/candida-0618 |access-date=2025-02-26 |website=MIT News {{!}} Massachusetts Institute of Technology |language=en}}</ref><ref>{{Cite web |last1=California |first1=University of |last2=Irvine |title=Scientists invent new drug candidates to treat antibiotic-resistant bacteria |url=https://phys.org/news/2025-02-scientists-drug-candidates-antibiotic-resistant.html |access-date=2025-02-26 |website=phys.org |language=en}}</ref>

== Types of opportunistic infections == {{Further|Immunodeficiency}}

Opportunistic infections can be caused by a wide variety of different types of pathogens. These infections can be caused by viral, bacterial, fungal, as well as parasitic pathogens.<ref>{{Cite web |date=2023-10-26 |title=Opportunistic infections |url=https://dermnetnz.org/topics/opportunistic-infections |access-date=2025-03-07 |website=DermNet® |language=en}}</ref>

A partial list of opportunistic pathogens and their associated effects are as follows:

=== Bacteria === * [https://pmc.ncbi.nlm.nih.gov/articles/PMC6560015/ Atopobium vaginae] is an anaerobic bacterium recognized for its role in the development of bacterial vaginosis (BV).<ref>{{Cite journal |last1=Mendling |first1=Werner |last2=Palmeira-de-Oliveira |first2=Ana |last3=Biber |first3=Stephan |last4=Prasauskas |first4=Valdas |date=July 2019 |title=An update on the role of Atopobium vaginae in bacterial vaginosis: what to consider when choosing a treatment? A mini review |journal=Archives of Gynecology and Obstetrics |volume=300 |issue=1 |pages=1–6 |doi=10.1007/s00404-019-05142-8 |issn=1432-0711 |pmc=6560015 |pmid=30953190}}</ref> * ''Clostridioides difficile'' (formerly known as ''Clostridium difficile'') is a bacteria that is known to cause gastrointestinal infection and diarrhea. It is typically associated with being the most common hospital acquired infection.<ref>{{cite journal |display-authors=6 |vauthors=Czepiel J, Dróżdż M, Pituch H, Kuijper EJ, Perucki W, Mielimonka A, Goldman S, Wultańska D, Garlicki A, Biesiada G |date=July 2019 |title=Clostridium difficile infection: review |journal=European Journal of Clinical Microbiology & Infectious Diseases |volume=38 |issue=7 |pages=1211–1221 |doi=10.1007/s10096-019-03539-6 |pmc=6570665 |pmid=30945014}}</ref><ref>{{cite journal |vauthors=Guh AY, Kutty PK |date=October 2018 |title=Clostridioides difficile Infection |journal=Annals of Internal Medicine |volume=169 |issue=7 |pages=ITC49–ITC64 |doi=10.7326/AITC201810020 |pmc=6524133 |pmid=30285209}}</ref> * Cutibacterium acnes (formerly [https://emedicine.medscape.com/article/226337-clinical?form=fpf Propionibacterium acnes]) can act as an opportunistic agent in infections associated with implanted medical devices, forming biofilms.<ref>{{Cite web |title=Cutibacterium (Propionibacterium) Infections Clinical Presentation: History, Complications |url=https://emedicine.medscape.com/article/226337-clinical?form=fpf |access-date=2025-04-26 |website=emedicine.medscape.com}}</ref> * [https://pmc.ncbi.nlm.nih.gov/articles/PMC4676548/ Extraintestinal pathogenic Escherichia coli (ExPEC)] are ''E. coli'' strains that can lead to diseases beyond the gut, notably urinary tract infections (UTIs), meningitis, and bacteremia (bloodstream infections).<ref>{{Cite journal |last1=Poolman |first1=Jan T. |last2=Wacker |first2=Michael |date=2016-01-01 |title=Extraintestinal Pathogenic Escherichia coli, a Common Human Pathogen: Challenges for Vaccine Development and Progress in the Field |journal=The Journal of Infectious Diseases |volume=213 |issue=1 |pages=6–13 |doi=10.1093/infdis/jiv429 |issn=1537-6613 |pmc=4676548 |pmid=26333944}}</ref> * [https://www.ncbi.nlm.nih.gov/books/NBK562176/ Haemophilus influenzae] is a bacterium implicated in causing illnesses such as meningitis, epiglottitis which can obstruct airways, pneumonia, otitis media affecting the ear, sinusitis involving the sinuses, and potentially leading to complications like mastoiditis, parameningeal abscess, and pericarditis.<ref>{{Citation |last1=Khattak |first1=Zoia E. |title=Haemophilus influenzae Infection |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK562176/ |access-date=2025-04-26 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32965847 |last2=Anjum |first2=Fatima}}</ref> * Klebsiella pneumoniae, a member of a group including pathogens, can be responsible for various infections in hospitalized individuals as it is frequently isolated from hospital admissions and the broader group (''[https://www.ncbi.nlm.nih.gov/books/NBK8035/ Enterobacteriaceae]'') is known to cause diverse infections.<ref>{{Citation |last=Guentzel |first=M. Neal |title=Escherichia, Klebsiella, Enterobacter, Serratia, Citrobacter, and Proteus |date=1996 |work=Medical Microbiology |editor-last=Baron |editor-first=Samuel |url=https://www.ncbi.nlm.nih.gov/books/NBK8035/ |access-date=2025-04-26 |edition=4th |place=Galveston (TX) |publisher=University of Texas Medical Branch at Galveston |isbn=978-0-9631172-1-2 |pmid=21413290}}</ref> * ''Legionella pneumophila'' is a bacterium that causes Legionnaire's disease, a respiratory infection.<ref>{{cite journal | vauthors = Chahin A, Opal SM | title = Severe Pneumonia Caused by Legionella pneumophila: Differential Diagnosis and Therapeutic Considerations | journal = Infectious Disease Clinics of North America | volume = 31 | issue = 1 | pages = 111–121 | date = March 2017 | pmid = 28159171 | pmc = 7135102 | doi = 10.1016/j.idc.2016.10.009 }}</ref><ref>{{cite journal | vauthors = Berjeaud JM, Chevalier S, Schlusselhuber M, Portier E, Loiseau C, Aucher W, Lesouhaitier O, Verdon J | display-authors = 6 | title = Legionella pneumophila: The Paradox of a Highly Sensitive Opportunistic Waterborne Pathogen Able to Persist in the Environment | journal = Frontiers in Microbiology | volume = 7 | page = 486 | date = 2016-04-08 | pmid = 27092135 | pmc = 4824771 | doi = 10.3389/fmicb.2016.00486 | doi-access = free | bibcode = 2016FrMic...700486B }}</ref> * ''Mycobacterium avium complex'' (MAC) is a group of two bacteria, ''M. avium'' and ''M. intracellulare'', that typically co-infect, leading to a lung infection called mycobacterium avium-intracellulare infection.<ref>{{cite journal | vauthors = Falkinham JO | title = ''Mycobacterium avium'' complex: Adherence as a way of life | journal = AIMS Microbiology | volume = 4 | issue = 3 | pages = 428–438 | date = 2018 | pmid = 31294225 | pmc = 6604937 | doi = 10.3934/microbiol.2018.3.428 }}</ref><ref>{{cite journal | vauthors = Pan SW, Shu CC, Feng JY, Su WJ | title = Treatment for Mycobacterium avium complex lung disease | journal = Journal of the Formosan Medical Association = Taiwan Yi Zhi | volume = 119 | pages = S67–S75 | date = June 2020 | issue = Suppl 1 | pmid = 32446754 | doi = 10.1016/j.jfma.2020.05.006 | doi-access = free }}</ref> * ''Mycobacterium tuberculosis'' is a species of bacteria that causes tuberculosis, a respiratory infection.<ref>{{cite journal | vauthors = Gordon SV, Parish T | title = Microbe Profile: Mycobacterium tuberculosis: Humanity's deadly microbial foe | journal = Microbiology | volume = 164 | issue = 4 | pages = 437–439 | date = April 2018 | pmid = 29465344 | doi = 10.1099/mic.0.000601 | doi-access = free }}</ref> * ''Pseudomonas aeruginosa'' is a bacterium that can cause respiratory infections. It is frequently associated with nosocomial infections and cystic fibrosis which can lead to organ dysfunctions and shortened life expectancy.<ref>{{cite journal |vauthors=Pang Z, Raudonis R, Glick BR, Lin TJ, Cheng Z |date=January–February 2019 |title=Antibiotic resistance in Pseudomonas aeruginosa: mechanisms and alternative therapeutic strategies |journal=Biotechnology Advances |volume=37 |issue=1 |pages=177–192 |doi=10.1016/j.biotechadv.2018.11.013 |pmid=30500353 |doi-access=free}}</ref><ref>{{Cite journal |last1=Ong |first1=Thida |last2=Ramsey |first2=Bonnie W. |date=2023-06-06 |title=Cystic Fibrosis: A Review |url=https://jamanetwork.com/journals/jama/article-abstract/2805701 |journal=JAMA |volume=329 |issue=21 |pages=1859–1871 |doi=10.1001/jama.2023.8120 |pmid=37278811 |issn=0098-7484|url-access=subscription }}</ref> * ''Salmonella'' is a genus of bacteria that is known to cause gastrointestinal infections causing an inflammatory response accompanied with fever and diarrhea.<ref>{{cite journal |vauthors=Lamas A, Miranda JM, Regal P, Vázquez B, Franco CM, Cepeda A |date=January 2018 |title=A comprehensive review of non-enterica subspecies of Salmonella enterica |journal=Microbiological Research |volume=206 |pages=60–73 |doi=10.1016/j.micres.2017.09.010 |pmid=29146261 |doi-access= |bibcode=2018MbRes.206...60L }}</ref><ref>{{Cite journal |last1=Coburn |first1=Bryan |last2=Grassl |first2=Guntram A |last3=Finlay |first3=B B |date=2007 |title=Salmonella, the host and disease: a brief review |url=https://onlinelibrary.wiley.com/doi/full/10.1038/sj.icb.7100007 |journal=Immunology & Cell Biology |language=en |volume=85 |issue=2 |pages=112–118 |doi=10.1038/sj.icb.7100007 |pmid=17146467 |issn=1440-1711|url-access=subscription }}</ref> * ''Staphylococcus aureus'' is a bacterium known to cause skin infections and sepsis, among other pathologies. Notably, ''S. aureus'' has evolved several drug-resistant strains, including MRSA.<ref>{{cite journal | vauthors = Jenul C, Horswill AR | title = Regulation of ''Staphylococcus aureus'' Virulence | journal = Microbiology Spectrum | volume = 7 | issue = 2 | date = April 2019 | article-number = 7.2.29 | pmid = 30953424 | pmc = 6452892 | doi = 10.1128/microbiolspec.GPP3-0031-2018 }}</ref><ref>{{cite journal | vauthors = Kong C, Neoh HM, Nathan S | title = Targeting Staphylococcus aureus Toxins: A Potential form of Anti-Virulence Therapy | journal = Toxins | volume = 8 | issue = 3 | page = 72 | date = March 2016 | pmid = 26999200 | pmc = 4810217 | doi = 10.3390/toxins8030072 | doi-access = free }}</ref> * [https://academic.oup.com/jacamr/article/4/3/dlac040/6580717 Stenotrophomonas maltophilia] has emerged as a challenging nosocomial agent frequently associated with respiratory tract infections like pneumonia and exacerbations in individuals with COPD, and can also cause bacteremia, particularly linked to central lines in vulnerable patients.<ref>{{Cite journal |last1=Mojica |first1=Maria F. |last2=Humphries |first2=Romney |last3=Lipuma |first3=John J. |last4=Mathers |first4=Amy J. |last5=Rao |first5=Gauri G. |last6=Shelburne |first6=Samuel A. |last7=Fouts |first7=Derrick E. |last8=Van Duin |first8=David |last9=Bonomo |first9=Robert A. |date=2022-06-01 |title=Clinical challenges treating Stenotrophomonas maltophilia infections: an update |url=https://academic.oup.com/jacamr/article/4/3/dlac040/6580717 |journal=JAC-Antimicrobial Resistance |volume=4 |issue=3 |article-number=dlac040 |doi=10.1093/jacamr/dlac040 |pmid=35529051 |pmc=9071536 |issn=2632-1823}}</ref> * ''Streptococcus pneumoniae'' is a bacterium that causes respiratory infections as well as meningitis and bacteremia.'''<ref name=":22">{{cite journal |vauthors=Schroeder MR, Stephens DS |date=2016-09-21 |title=Macrolide Resistance in ''Streptococcus pneumoniae'' |journal=Frontiers in Cellular and Infection Microbiology |volume=6 |page=98 |doi=10.3389/fcimb.2016.00098 |pmc=5030221 |pmid=27709102 |doi-access=free}}</ref><ref>{{Cite journal |last1=Lynch |first1=Joseph P. |last2=Zhanel |first2=George G. |date=April 2009 |title=Streptococcus pneumoniae: Epidemiology, Risk Factors, and Strategies for Prevention |url=https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-0029-1202938 |journal=Seminars in Respiratory and Critical Care Medicine |language=en |volume=30 |issue=2 |pages=189–209 |doi=10.1055/s-0029-1202938 |pmid=19296419 |issn=1069-3424|url-access=subscription }}</ref>''' * ''Streptococcus pyogenes'' (also known as group A ''Streptococcus'') is a bacterium that can cause a variety of conditions, including impetigo and strep throat, as well as other illnesses.<ref>{{cite journal | vauthors = Jespersen MG, Lacey JA, Tong SY, Davies MR | title = Global genomic epidemiology of Streptococcus pyogenes | journal = Infection, Genetics and Evolution | volume = 86 | article-number = 104609 | date = December 2020 | pmid = 33147506 | doi = 10.1016/j.meegid.2020.104609 | doi-access = free | bibcode = 2020InfGE..8604609J }}</ref><ref>{{cite journal | vauthors = Brouwer S, Barnett TC, Rivera-Hernandez T, Rohde M, Walker MJ | title = Streptococcus pyogenes adhesion and colonization | journal = FEBS Letters | volume = 590 | issue = 21 | pages = 3739–3757 | date = November 2016 | pmid = 27312939 | doi = 10.1002/1873-3468.12254 | hdl = 10033/619157 | s2cid = 205213711 | hdl-access = free }}</ref>

=== Fungi === * ''Aspergillus'' is a fungus, commonly associated with respiratory infection.<ref>{{cite journal | vauthors = Latgé JP, Chamilos G | title = Aspergillus fumigatus and Aspergillosis in 2019 | journal = Clinical Microbiology Reviews | volume = 33 | issue = 1 | pages = e00140–18, /cmr/33/1/CMR.00140–18.atom | date = December 2019 | article-number = e00140-18 | pmid = 31722890 | pmc = 6860006 | doi = 10.1128/CMR.00140-18 }}</ref><ref name=":3">{{cite journal | vauthors = José RJ, Periselneris JN, Brown JS | title = Opportunistic bacterial, viral and fungal infections of the lung | journal = Medicine | volume = 48 | issue = 6 | pages = 366–372 | date = June 2020 | pmid = 32390758 | pmc = 7206443 | doi = 10.1016/j.mpmed.2020.03.006 }}</ref> * ''Candida albicans'' is a species of fungus that is a part of the normal human microbiome. It acts as a commensal unless there is a change in concentrations. It can be associated with various conditions such as oral thrush and gastrointestinal infection.<ref>{{cite journal |vauthors=Akpan A, Morgan R |date=August 2002 |title=Oral candidiasis |journal=Postgraduate Medical Journal |volume=78 |issue=922 |pages=455–9 |doi=10.1136/pmj.78.922.455 |pmc=1742467 |pmid=12185216}}</ref><ref>{{cite journal |vauthors=Erdogan A, Rao SS |date=April 2015 |title=Small intestinal fungal overgrowth |journal=Current Gastroenterology Reports |volume=17 |issue=4 |article-number=16 |doi=10.1007/s11894-015-0436-2 |pmid=25786900 |s2cid=3098136}}</ref><ref>{{Cite journal |last1=Mayer |first1=François L. |last2=Wilson |first2=Duncan |last3=Hube |first3=Bernhard |date=2013-02-15 |title=Candida albicans pathogenicity mechanisms |journal=Virulence |volume=4 |issue=2 |pages=119–128 |doi=10.4161/viru.22913 |issn=2150-5594 |pmc=3654610 |pmid=23302789}}</ref> * ''Coccidioides immitis'' is a fungus known for causing coccidioidomycosis, more commonly known as Valley Fever.<ref>{{cite journal | vauthors = Mu A, Shein TT, Jayachandran P, Paul S | title = Immune Reconstitution Inflammatory Syndrome in Patients with AIDS and Disseminated Coccidioidomycosis: A Case Series and Review of the Literature | journal = Journal of the International Association of Providers of AIDS Care | volume = 16 | issue = 6 | pages = 540–545 | date = 2017-09-14 | pmid = 28911256 | doi = 10.1177/2325957417729751 | doi-access = free }}</ref> * [https://pmc.ncbi.nlm.nih.gov/articles/PMC3318971/ Cryptococcus gattii]: This emerging fungal pathogen can cause severe and often fatal infections, manifesting as pulmonary disease and meningitis in both immunocompromised and immunocompetent individuals.<ref>{{Cite journal |last1=Byrnes |first1=Edmond J. |last2=Bartlett |first2=Karen H. |last3=Perfect |first3=John R. |last4=Heitman |first4=Joseph |date=October 2011 |title=Cryptococcus gattii: an emerging fungal pathogen infecting humans and animals |journal=Microbes and Infection |volume=13 |issue=11 |pages=895–907 |doi=10.1016/j.micinf.2011.05.009 |issn=1769-714X |pmc=3318971 |pmid=21684347}}</ref> * ''Cryptococcus neoformans'' is a fungus that causes cryptococcosis, which can lead to pulmonary infection as well as nervous system infections, like meningitis.<ref>{{cite journal | vauthors = Kwon-Chung KJ, Fraser JA, Doering TL, Wang Z, Janbon G, Idnurm A, Bahn YS | title = Cryptococcus neoformans and Cryptococcus gattii, the etiologic agents of cryptococcosis | journal = Cold Spring Harbor Perspectives in Medicine | volume = 4 | issue = 7 | article-number = a019760 | date = July 2014 | pmid = 24985132 | pmc = 4066639 | doi = 10.1101/cshperspect.a019760 }}</ref><ref>{{cite journal | vauthors = Maziarz EK, Perfect JR | title = Cryptococcosis | journal = Infectious Disease Clinics of North America | volume = 30 | issue = 1 | pages = 179–206 | date = March 2016 | pmid = 26897067 | pmc = 5808417 | doi = 10.1016/j.idc.2015.10.006 }}</ref> * [https://pubmed.ncbi.nlm.nih.gov/14708965/ Dematiaceous (pigmented) molds]: These fungi are responsible for a range of diseases including phaeohyphomycosis, chromoblastomycosis, eumycotic mycetoma, invasive sinusitis, and allergic fungal sinusitis; cerebral infections can also occur.<ref>{{Cite journal |last1=Brandt |first1=M. E. |last2=Warnock |first2=D. W. |date=November 2003 |title=Epidemiology, clinical manifestations, and therapy of infections caused by dematiaceous fungi |journal=Journal of Chemotherapy (Florence, Italy) |volume=15 Suppl 2 |pages=36–47 |doi=10.1179/joc.2003.15.Supplement-2.36 |issn=1120-009X |pmid=14708965}}</ref> * [https://www.adelaide.edu.au/mycology/fungal-descriptions-and-antifungal-susceptibility/hyphomycetes-conidial-moulds/fusarium Fusarium species]: These fungi can cause hyalohyphomycosis, particularly in immunocompromised individuals, as well as mycotic keratitis and onychomycosis.<ref>{{Cite web |last=Ellis |first=David |date=2026-04-19 |title=Fusarium |url=https://www.adelaide.edu.au/mycology/fungal-descriptions-and-antifungal-susceptibility/hyphomycetes-conidial-moulds/fusarium |website=www.adelaide.edu.au}}</ref> * [https://pmc.ncbi.nlm.nih.gov/articles/PMC9964096/ Hyaline (non-pigmented) molds] (e.g., ''Acremonium'', ''Paecilomyces'', ''Scopulariopsis'' species): This group encompasses various molds, including ''[https://www.adelaide.edu.au/mycology/fungal-descriptions-and-antifungal-susceptibility/hyphomycetes-conidial-moulds/fusarium Fusarium spp].'' causing hyalohyphomycosis, mycotic keratitis, and onychomycosis, as well as commonly causing pneumonia, sinusitis, and cutaneous lesions that may disseminate in neutropenic patients; ''[https://pmc.ncbi.nlm.nih.gov/articles/PMC2223844/ Scedosporium spp].'' associated with sinusitis and pneumonia; ''Lomentospora prolificans'' causing a varied range of infections and disseminated disease; ''Scopulariopsis spp.'' and ''Acremonium spp.'' linked to sinopulmonary diseases; ''Paecilomyces variotii'' causing sinopulmonary disease; and ''Penicillium species'' implicated in necrotizing esophagitis and disseminated infections.<ref>{{Cite journal |last1=Jacobs |first1=Samantha E. |last2=Walsh |first2=Thomas J. |date=2023-02-06 |title=Non-Aspergillus Hyaline Molds: A Host-Based Perspective of Emerging Pathogenic Fungi Causing Sinopulmonary Diseases |journal=Journal of Fungi (Basel, Switzerland) |volume=9 |issue=2 |page=212 |doi=10.3390/jof9020212 |doi-access=free |issn=2309-608X |pmc=9964096 |pmid=36836326}}</ref> * ''Histoplasma capsulatum'' is a species of fungus known to cause histoplasmosis, which can present itself with an array of symptoms, but often involves respiratory infection.<ref>{{cite journal | vauthors = Horwath MC, Fecher RA, Deepe GS | title = Histoplasma capsulatum, lung infection and immunity | journal = Future Microbiology | volume = 10 | issue = 6 | pages = 967–75 | date = 2015-06-10 | pmid = 26059620 | pmc = 4478585 | doi = 10.2217/fmb.15.25 }}</ref><ref>{{cite book | vauthors = Mittal J, Ponce MG, Gendlina I, Nosanchuk JD | title = Fungal Physiology and Immunopathogenesis | chapter = Histoplasma Capsulatum: Mechanisms for Pathogenesis | series = Current Topics in Microbiology and Immunology | volume = 422 | pages = 157–191 | date = 2018 | pmid = 30043340 | pmc = 7212190 | doi = 10.1007/82_2018_114 | publisher = Springer International Publishing | isbn = 978-3-030-30236-8 | place = Cham | veditors = Rodrigues ML }}</ref> * [https://pmc.ncbi.nlm.nih.gov/articles/PMC9316904/ Lomentospora prolificans]: This fungus can cause a remarkably varied range of infections and disseminated disease, including keratitis, mycotic aneurysms, external otitis, sinusitis, peritonitis, onychomycosis, and esophagitis.<ref>{{Cite journal |last1=Konsoula |first1=Afroditi |last2=Tsioutis |first2=Constantinos |last3=Markaki |first3=Ioulia |last4=Papadakis |first4=Michail |last5=Agouridis |first5=Aris P. |last6=Spernovasilis |first6=Nikolaos |date=2022-06-29 |title=Lomentospora prolificans: An Emerging Opportunistic Fungal Pathogen |journal=Microorganisms |volume=10 |issue=7 |page=1317 |doi=10.3390/microorganisms10071317 |doi-access=free |issn=2076-2607 |pmc=9316904 |pmid=35889036}}</ref> * ''Pseudogymnoascus destructans'' (formerly known as ''Geomyces destructans'') is a fungus that causes white-nose syndrome in bats.<ref>{{cite journal | vauthors = Seyedmousavi S, Bosco SM, de Hoog S, Ebel F, Elad D, Gomes RR, Jacobsen ID, Jensen HE, Martel A, Mignon B, Pasmans F, Piecková E, Rodrigues AM, Singh K, Vicente VA, Wibbelt G, Wiederhold NP, Guillot J | display-authors = 6 | title = Fungal infections in animals: a patchwork of different situations | journal = Medical Mycology | volume = 56 | issue = suppl_1 | pages = 165–187 | date = April 2018 | pmid = 29538732 | pmc = 6251577 | doi = 10.1093/mmy/myx104 }}</ref> * ''Microsporidia'' is a group of fungi that infect species across the animal kingdom, one species of which can cause microsporidiosis in immunocompromised human hosts.<ref>{{cite journal | vauthors = Stentiford GD, Becnel JJ, Weiss LM, Keeling PJ, Didier ES, Bjornson S, Freeman MA, Brown MJ, Roesel K, Sokolova Y, Snowden KF, Solter L | display-authors = 6 | title = Microsporidia - Emergent Pathogens in the Global Food Chain | journal = Trends in Parasitology | volume = 32 | issue = 4 | pages = 336–348 | date = April 2016 | pmid = 26796229 | pmc = 4818719 | doi = 10.1016/j.pt.2015.12.004 }}</ref> * ''Pneumocystis jirovecii'' (formerly known as ''Pneumocystis carinii'') is a fungus that causes pneumocystis pneumonia, a respiratory infection.<ref>{{cite journal | vauthors = Sokulska M, Kicia M, Wesołowska M, Hendrich AB | title = Pneumocystis jirovecii--from a commensal to pathogen: clinical and diagnostic review | journal = Parasitology Research | volume = 114 | issue = 10 | pages = 3577–85 | date = October 2015 | pmid = 26281787 | pmc = 4562001 | doi = 10.1007/s00436-015-4678-6 }}</ref> * [https://pmc.ncbi.nlm.nih.gov/articles/PMC3469092/ Rhodotorula species]: These yeasts can cause fungemia, often linked to central venous catheter use, as well as localized infections including meningitis, skin infections, ocular infections, peritonitis, and prosthetic joint infections. * [https://pmc.ncbi.nlm.nih.gov/articles/PMC100153/ Zygomycetes] (e.g., ''Mucor'', ''Rhizopus'', ''Absidia''): This group can cause infections like rhinocerebral mucormycosis, and ''Mucor'' has been associated with respiratory infections; specifically, ''Absidia corymbifera'' is considered a human pathogen.<ref>{{Cite journal |last1=Ribes |first1=J. A. |last2=Vanover-Sams |first2=C. L. |last3=Baker |first3=D. J. |date=April 2000 |title=Zygomycetes in human disease |journal=Clinical Microbiology Reviews |volume=13 |issue=2 |pages=236–301 |doi=10.1128/CMR.13.2.236 |issn=0893-8512 |pmc=100153 |pmid=10756000 |bibcode=2000CliMR..13..236R }}</ref>

=== Protozoa === * ''Cryptosporidium'' is a protozoan that causes the condition Cryptosporidiosis. This condition affects the gastrointestinal tract.<ref>{{cite journal |vauthors=Gerace E, Lo Presti VD, Biondo C |date=December 2019 |title=''Cryptosporidium'' Infection: Epidemiology, Pathogenesis, and Differential Diagnosis |journal=European Journal of Microbiology & Immunology |volume=9 |issue=4 |pages=119–123 |doi=10.1556/1886.2019.00019 |pmc=6945992 |pmid=31934363}}</ref><ref>{{Cite journal |last1=Pumipuntu |first1=Natapol |last2=Piratae |first2=Supawadee |date=May 2018 |title=Cryptosporidiosis: A zoonotic disease concern |journal=Veterinary World |language=en |volume=11 |issue=5 |pages=681–686 |doi=10.14202/vetworld.2018.681-686 |pmid=29915508 |pmc=5993756 |issn=0972-8988 }}</ref> * ''Toxoplasma gondii'' is a protozoan, known for causing toxoplasmosis which is known to lead to impairment of the brain.<ref>{{cite journal |vauthors=Mendez OA, Koshy AA |date=July 2017 |title=Toxoplasma gondii: Entry, association, and physiological influence on the central nervous system |journal=PLOS Pathogens |volume=13 |issue=7 |article-number=e1006351 |doi=10.1371/journal.ppat.1006351 |pmc=5519211 |pmid=28727854 |doi-access=free |veditors=Gubbels MJ}}</ref><ref>{{cite journal |vauthors=Hunter CA, Sibley LD |date=November 2012 |title=Modulation of innate immunity by Toxoplasma gondii virulence effectors |journal=Nature Reviews. Microbiology |volume=10 |issue=11 |pages=766–78 |doi=10.1038/nrmicro2858 |pmc=3689224 |pmid=23070557}}</ref><ref>{{Cite journal |last1=Samojłowicz |first1=Dorota |last2=Twarowska-Małczyńska |first2=Joanna |last3=Borowska-Solonynko |first3=Aleksandra |last4=Poniatowski |first4=Łukasz A. |last5=Sharma |first5=Nipika |last6=Olczak |first6=Mieszko |date=2019-02-01 |title=Presence of Toxoplasma gondii infection in brain as a potential cause of risky behavior: a report of 102 autopsy cases |journal=European Journal of Clinical Microbiology & Infectious Diseases |language=en |volume=38 |issue=2 |pages=305–317 |doi=10.1007/s10096-018-3427-z |issn=1435-4373 |pmc=6514116 |pmid=30470966}}</ref>

=== Viruses === * [https://www.ncbi.nlm.nih.gov/books/NBK559072/ Adenovirus] is known to cause various illnesses, including lower respiratory tract infections, pneumonia, acute respiratory diseases, epidemic keratoconjunctivitis affecting the eyes, acute hemorrhagic cystitis of the bladder, and gastroenteritis affecting the digestive system.<ref>{{Citation |last1=Usman |first1=Norina |title=Adenoviruses |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK559072/ |access-date=2025-04-26 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32644498 |last2=Suarez |first2=Manuel}}</ref> * LCMV causes lymphocytic choriomeningitis disease and death in immunocompromised organ-transplant patients.<ref>{{Cite journal |last1=Witwit |first1=Haydar |last2=Betancourt |first2=Carlos Alberto |last3=Cubitt |first3=Beatrice |last4=Khafaji |first4=Roaa |last5=Kowalski |first5=Heinrich |last6=Jackson |first6=Nathaniel |last7=Ye |first7=Chengjin |last8=Martinez-Sobrido |first8=Luis |last9=de la Torre |first9=Juan C. |date=2024-08-26 |title=Cellular N-Myristoyl Transferases Are Required for Mammarenavirus Multiplication |journal=Viruses |language=en |volume=16 |issue=9 |pages=1362 |doi=10.3390/v16091362 |doi-access=free |issn=1999-4915 |pmc=11436053 |pmid=39339839}}</ref><ref>{{Cite journal |last1=Witwit |first1=Haydar |last2=Khafaji |first2=Roaa |last3=Salaniwal |first3=Arul |last4=Kim |first4=Arthur S. |last5=Cubitt |first5=Beatrice |last6=Jackson |first6=Nathaniel |last7=Ye |first7=Chengjin |last8=Weiss |first8=Susan R. |last9=Martinez-Sobrido |first9=Luis |last10=de la Torre |first10=Juan Carlos |date=2024-02-20 |title=Activation of protein kinase receptor (PKR) plays a pro-viral role in mammarenavirus-infected cells |journal=Journal of Virology |volume=98 |issue=3 |pages=e01883–23 |doi=10.1128/jvi.01883-23 |pmc=10949842 |pmid=38376197}}</ref><ref>{{Cite journal |last1=Fischer |first1=Staci A. |last2=Graham |first2=Mary Beth |last3=Kuehnert |first3=Matthew J. |last4=Kotton |first4=Camille N. |last5=Srinivasan |first5=Arjun |last6=Marty |first6=Francisco M. |last7=Comer |first7=James A. |last8=Guarner |first8=Jeannette |last9=Paddock |first9=Christopher D. |last10=DeMeo |first10=Dawn L. |last11=Shieh |first11=Wun-Ju |last12=Erickson |first12=Bobbie R. |last13=Bandy |first13=Utpala |last14=DeMaria |first14=Alfred |last15=Davis |first15=Jeffrey P. |date=2006-05-25 |title=Transmission of Lymphocytic Choriomeningitis Virus by Organ Transplantation |url=http://www.nejm.org/doi/abs/10.1056/NEJMoa053240 |journal=New England Journal of Medicine |language=en |volume=354 |issue=21 |pages=2235–2249 |doi=10.1056/NEJMoa053240 |pmid=16723615 |issn=0028-4793}}</ref><ref>{{Cite journal |last1=Samstein |first1=B. |last2=Smith |first2=A. |last3=Freise |first3=C. |last4=Zimmerman |first4=M. |last5=Baker |first5=T. |last6=Olthoff |first6=K. |last7=Fisher |first7=R. |last8=Merion |first8=R. |date=July 2014 |title=Post-Transplant Complications in Recipients of Deceased and Living Donor Liver Transplant. |url=https://doi.org/10.1097/00007890-201407151-00001 |journal=Transplantation |volume=98 |pages=2 |doi=10.1097/00007890-201407151-00001 |issn=0041-1337|url-access=subscription }}</ref><ref>{{Cite journal |last1=Sayyad |first1=Leanna E |last2=Smith |first2=Kami L |last3=Sadigh |first3=Katrin S |last4=Cossaboom |first4=Caitlin M |last5=Choi |first5=Mary J |last6=Whitmer |first6=Shannon |last7=Cannon |first7=Debi |last8=Krapiunaya |first8=Inna |last9=Morales-Betoulle |first9=Maria |last10=Annambhotla |first10=Pallavi |last11=Basavaraju |first11=Sridhar V |last12=Ruberto |first12=Irene |last13=Kretschmer |first13=Melissa |last14=Gutierrez |first14=Nalleli |last15=Zabel |first15=Karen |date=2025-01-31 |title=Severe Non–Donor-Derived Lymphocytic Choriomeningitis Virus Infection in 2 Solid Organ Transplant Recipients |journal=Open Forum Infectious Diseases |language=en |volume=12 |issue=2 |article-number=ofaf002 |doi=10.1093/ofid/ofaf002 |issn=2328-8957 |pmc=11783784 |pmid=39896983}}</ref> * HSV is considered a member of the human herpesvirus family and is most frequently associated with immunocompromisation diseases and JAK inhibitors.<ref>{{Cite journal |last1=Witwit |first1=Haydar |last2=de la Torre |first2=Juan C. |date=2025-10-01 |title=N-myristoyltransferase inhibitors as candidate broad-spectrum antivirals to treat viral infections promoted by immunosuppression associated with JAK inhibitors therapy |url=https://www.sciencedirect.com/science/article/pii/S0166354225001846 |journal=Antiviral Research |volume=242 |article-number=106258 |doi=10.1016/j.antiviral.2025.106258 |pmid=40803634 |issn=0166-3542|url-access=subscription }}</ref><ref>{{Cite journal |last=Ljungman |first=Per |date=January 1993 |title=Herpes Virus Infections in Immunocompromised Patients: Problems and Therapeutic Interventions |url=http://www.tandfonline.com/doi/full/10.3109/07853899309147293 |journal=Annals of Medicine |language=en |volume=25 |issue=4 |pages=329–333 |doi=10.3109/07853899309147293 |pmid=8217097 |issn=0785-3890|url-access=subscription }}</ref><ref>{{Cite journal |last1=Reid |first1=Gail |last2=Lynch |first2=Joseph |last3=Weigt |first3=Samuel |last4=Sayah |first4=David |last5=Belperio |first5=John |last6=Grim |first6=Shellee |last7=Clark |first7=Nina |date=2016-08-03 |title=Herpesvirus Respiratory Infections in Immunocompromised Patients: Epidemiology, Management, and Outcomes |journal=Seminars in Respiratory and Critical Care Medicine |language=en |volume=37 |issue=4 |pages=603–630 |doi=10.1055/s-0036-1584793 |issn=1069-3424 |pmc=7171758 |pmid=27486740}}</ref><ref>{{Cite journal |last1=Piperi |first1=Evangelia |last2=Papadopoulou |first2=Erofili |last3=Georgaki |first3=Maria |last4=Dovrat |first4=Sara |last5=Bar Illan |first5=Mor |last6=Nikitakis |first6=Nikolaos G. |last7=Yarom |first7=Noam |date=2024 |title=Management of oral herpes simplex virus infections: The problem of resistance. A narrative review |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/odi.14635 |journal=Oral Diseases |language=en |volume=30 |issue=3 |pages=877–894 |doi=10.1111/odi.14635 |pmid=37279074 |issn=1601-0825|doi-access=free }}</ref> * ''Cytomegalovirus'' is considered a member of the human herpesvirus family and is most frequently associated with respiratory infection.<ref name=":33">{{cite journal |vauthors=José RJ, Periselneris JN, Brown JS |date=June 2020 |title=Opportunistic bacterial, viral and fungal infections of the lung |journal=Medicine |volume=48 |issue=6 |pages=366–372 |doi=10.1016/j.mpmed.2020.03.006 |pmc=7206443 |pmid=32390758}}</ref><ref>{{cite journal |vauthors=Fonseca Brito L, Brune W, Stahl FR |date=August 2019 |title=Cytomegalovirus (CMV) Pneumonitis: Cell Tropism, Inflammation, and Immunity |journal=International Journal of Molecular Sciences |volume=20 |issue=16 |page=3865 |doi=10.3390/ijms20163865 |pmc=6719013 |pmid=31398860 |doi-access=free}}</ref><ref>{{Citation |last1=Dioverti |first1=M. Veronica |title=Cytomegalovirus |date=2016 |work=Diagnostic Microbiology of the Immunocompromised Host |pages=97–125 |url=https://onlinelibrary.wiley.com/doi/abs/10.1128/9781555819040.ch4 |access-date=2025-03-07 |publisher=John Wiley & Sons, Ltd |language=en |doi=10.1128/9781555819040.ch4 |isbn=978-1-68367-070-4 |last2=Razonable |first2=Raymund R.|url-access=subscription }}</ref> * [https://www.ncbi.nlm.nih.gov/books/NBK555945/ Hepatitis B Virus (HBV)] can lead to acute liver infection manifesting as anicteric hepatitis, icteric hepatitis, or fulminant hepatitis, and chronic infection can progress to an asymptomatic carrier state, chronic hepatitis, cirrhosis of the liver, and hepatocellular carcinoma. Severe liver damage can result in complications like jaundice, hepatic encephalopathy, ascites, gastrointestinal bleeding, and coagulopathy.<ref>{{Citation |last1=Tripathi |first1=Nishant |title=Hepatitis B |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK555945/ |access-date=2025-04-26 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32310405 |last2=Mousa |first2=Omar Y.}}</ref> * [https://www.ncbi.nlm.nih.gov/books/NBK430897/ Hepatitis C Virus (HCV)] infection can become chronic, leading to liver damage that can progress to cirrhosis, portal hypertension, hepatic decompensation with encephalopathy, and hepatocellular carcinoma. * [https://www.cdc.gov/flu/about/index.html Influenza Virus] is responsible for seasonal flu epidemics and can be categorized into types affecting various hosts, such as avian (bird) flu, canine (dog) flu, swine (pig)/variant flu, and can cause pandemic flu, all generally resulting in respiratory illnesses.<ref>{{Cite web |last=CDC |date=2025-02-18 |title=About Influenza |url=https://www.cdc.gov/flu/about/index.html |access-date=2025-04-26 |website=Influenza (Flu) |language=en-us}}</ref> * [https://www.ncbi.nlm.nih.gov/books/NBK560910/ Human Metapneumovirus (HMPV)] commonly causes upper and lower respiratory tract infections, with symptoms such as cough, mucous production, fever, and dyspnea, and can lead to more severe conditions like pneumonia and bronchiolitis.<ref>{{Citation |last1=Uddin |first1=Sanaa |title=Human Metapneumovirus |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK560910/ |access-date=2025-04-26 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32809745 |last2=Thomas |first2=Meagan}}</ref> * [https://www.ncbi.nlm.nih.gov/books/NBK448132/ Human Papillomavirus (HPV)] is the initiating force behind multiple conditions, including cutaneous and anogenital warts, which in some cases can progress to various carcinomas.<ref>{{Citation |last1=Luria |first1=Lynette |title=Human Papillomavirus |date=2025 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK448132/ |access-date=2025-04-26 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=28846281 |last2=Cardoza-Favarato |first2=Gabriella}}</ref> * ''Human polyomavirus 2'' (also known as JC virus) is known to cause progressive multifocal leukoencephalopathy (PML) which affects the central nervous system.<ref>{{cite journal |vauthors=Bohra C, Sokol L, Dalia S |date=2017-11-01 |title=Progressive Multifocal Leukoencephalopathy and Monoclonal Antibodies: A Review |journal=Cancer Control |volume=24 |issue=4 |article-number=1073274817729901 |doi=10.1177/1073274817729901 |pmc=5937251 |pmid=28975841}}</ref><ref>{{cite journal |vauthors=Kartau M, Sipilä JO, Auvinen E, Palomäki M, Verkkoniemi-Ahola A |date=2019-12-02 |title=Progressive Multifocal Leukoencephalopathy: Current Insights |journal=Degenerative Neurological and Neuromuscular Disease |volume=9 |pages=109–121 |doi=10.2147/DNND.S203405 |pmc=6896915 |pmid=31819703 |doi-access=free}}</ref><ref>{{Cite journal |last=Weissert |first=Robert |date=2011-02-01 |title=Progressive multifocal leukoencephalopathy |url=https://www.sciencedirect.com/science/article/abs/pii/S0165572810004406 |journal=Journal of Neuroimmunology |series=Special Issue on Advances in Clinical Neuroimmunology |volume=231 |issue=1 |pages=73–77 |doi=10.1016/j.jneuroim.2010.09.021 |pmid=20937530 |issn=0165-5728|url-access=subscription }}</ref> * ''Human herpesvirus 8'' (also known as Kaposi sarcoma-associated herpesvirus) is a virus associated with Kaposi sarcoma, a type of skin cancer.<ref>{{cite journal |vauthors=Radu O, Pantanowitz L |date=February 2013 |title=Kaposi sarcoma |journal=Archives of Pathology & Laboratory Medicine |volume=137 |issue=2 |pages=289–94 |doi=10.5858/arpa.2012-0101-RS |pmid=23368874 |doi-access=}}</ref><ref>{{cite journal |vauthors=Cesarman E, Damania B, Krown SE, Martin J, Bower M, Whitby D |date=January 2019 |title=Kaposi sarcoma |journal=Nature Reviews. Disease Primers |volume=5 |issue=1 |article-number=9 |doi=10.1038/s41572-019-0060-9 |pmc=6685213 |pmid=30705286}}</ref> * [https://www.who.int/news-room/fact-sheets/detail/human-t-lymphotropic-virus-type-1 Human T-cell leukemia virus type 1 (HTLV-1)] causes a chronic lifelong infection that can lead to general immunosuppression, uveitis affecting the eyes, dermatitis of the skin, pneumonitis in the lungs, adult T-cell leukemia, and HTLV-1 associated myelopathy also known as tropical spastic paraparesis.<ref>{{Cite web |title=Human T-lymphotropic virus type 1 |url=https://www.who.int/news-room/fact-sheets/detail/human-t-lymphotropic-virus-type-1 |access-date=2025-04-26 |website=www.who.int |language=en}}</ref> * [https://www.cdc.gov/parainfluenza/about/index.html Parainfluenza Virus] commonly causes upper and lower respiratory illnesses with symptoms similar to the common cold, such as fever, runny nose, cough, sneezing, and sore throat, and can also cause more serious illnesses in children including croup, bronchitis, and bronchiolitis.<ref>{{Cite web |last=CDC |date=2024-06-18 |title=About Human Parainfluenza Viruses (HPIVs) |url=https://www.cdc.gov/parainfluenza/about/index.html |access-date=2025-04-26 |website=Parainfluenza |language=en-us}}</ref> * [https://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/coronavirus-disease-2019-covid19 SARS-CoV-2] is the virus that causes Coronavirus Disease 2019 (COVID-19), with symptoms that can include fever, cough, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, and diarrhea.<ref>{{Cite web |url=https://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/coronavirus-disease-2019-covid19 |access-date=2025-04-26 |website=www.pennmedicine.org}}</ref> * Varicella-Zoster Virus causes [https://www.cdc.gov/shingles/about/index.html Shingles].<ref>{{Cite web |last=CDC |date=2025-01-17 |title=About Shingles (Herpes Zoster) |url=https://www.cdc.gov/shingles/about/index.html |access-date=2025-04-26 |website=Shingles (Herpes Zoster) |language=en-us}}</ref><ref>{{Cite journal |last1=Witwit |first1=Haydar |last2=de la Torre |first2=Juan C. |date=2025-10-01 |title=N-myristoyltransferase inhibitors as candidate broad-spectrum antivirals to treat viral infections promoted by immunosuppression associated with JAK inhibitors therapy |url=https://www.sciencedirect.com/science/article/pii/S0166354225001846 |journal=Antiviral Research |volume=242 |article-number=106258 |doi=10.1016/j.antiviral.2025.106258 |pmid=40803634 |issn=0166-3542|url-access=subscription }}</ref>

== Opportunistic infections and HIV/AIDS == Human immunodeficiency virus (HIV) is a virus that targets the CD4 cells (a type of white blood cell) within the body's immune system and causes HIV disease or HIV/AIDS. CD4 counts within a non-affected immune system would range anywhere from 500-1500 cells per cubic millimeter of blood, while an affected immune system would show cell counts below 200.<ref>{{Cite journal |last1=Pilangorgi |first1=Sahar Souri |last2=Khodakarim |first2=Soheila |last3=Shayan |first3=Zahra |last4=Nejat |first4=Mehdi |date=2025-03-12 |title=Evaluation of factors related to longitudinal CD4 count and the risk of death among HIV-infected patients using Bayesian joint models |journal=BMC Public Health |volume=25 |issue=1 |page=979 |doi=10.1186/s12889-025-22096-6 |doi-access=free |issn=1471-2458 |pmc=11905675 |pmid=40075339}}</ref> HIV infection can lead to progressively worsening immunodeficiency, a condition ideal for the development of opportunistic infection.<ref>{{cite journal |vauthors=Doitsh G, Greene WC |date=March 2016 |title=Dissecting How CD4 T Cells Are Lost During HIV Infection |journal=Cell Host & Microbe |volume=19 |issue=3 |pages=280–91 |doi=10.1016/j.chom.2016.02.012 |pmc=4835240 |pmid=26962940}}</ref><ref>{{cite journal |vauthors=Fenwick C, Joo V, Jacquier P, Noto A, Banga R, Perreau M, Pantaleo G |date=November 2019 |title=T-cell exhaustion in HIV infection |journal=Immunological Reviews |volume=292 |issue=1 |pages=149–163 |doi=10.1111/imr.12823 |pmc=7003858 |pmid=31883174}}</ref> As HIV worsens over time, the term AIDS, or acquired immunodeficiency syndrome has been used to describe the condition and extensive damage to the immune system as well as the onset and susceptibility to other illnesses. The onset of AIDS leads to respiratory and central nervous system opportunistic infections, including but not limited to pneumonia, tuberculosis and meningitis.<ref>{{Cite web |title=HIV vs. AIDS: When Does HIV Turn Into AIDS? Differences |url=https://www.medicinenet.com/hiv_vs_aids/article.htm |access-date=2025-03-20 |website=MedicineNet |language=en}}</ref><ref>{{cite journal |vauthors=Bruchfeld J, Correia-Neves M, Källenius G |date=February 2015 |title=Tuberculosis and HIV Coinfection |journal=Cold Spring Harbor Perspectives in Medicine |volume=5 |issue=7 |article-number=a017871 |doi=10.1101/cshperspect.a017871 |pmc=4484961 |pmid=25722472}}</ref><ref>{{cite journal |vauthors=Tenforde MW, Shapiro AE, Rouse B, Jarvis JN, Li T, Eshun-Wilson I, Ford N |date=July 2018 |title=Treatment for HIV-associated cryptococcal meningitis |journal=The Cochrane Database of Systematic Reviews |volume=2018 |issue=7 |article-number=CD005647 |doi=10.1002/14651858.CD005647.pub3 |pmc=6513250 |pmid=30045416 |collaboration=Cochrane Infectious Diseases Group}}</ref> Kaposi's sarcoma, a virally associated cancer, and non-Hodgkin's lymphoma are two types of cancers that are generally defined as AIDS malignancies.<ref>{{cite journal |display-authors=6 |vauthors=Rees CA, Keating EM, Lukolyo H, Danysh HE, Scheurer ME, Mehta PS, Lubega J, Slone JS |date=August 2016 |title=Mapping the Epidemiology of Kaposi Sarcoma and Non-Hodgkin Lymphoma Among Children in Sub-Saharan Africa: A Review |journal=Pediatric Blood & Cancer |volume=63 |issue=8 |pages=1325–31 |doi=10.1002/pbc.26021 |pmc=7340190 |pmid=27082516}}</ref> As immune function declines and HIV-infection progresses to AIDS, individuals are at an increased risk of opportunistic infections that their immune systems are no longer capable of responding properly to. Because of this, opportunistic infections are a leading cause of HIV/AIDS-related deaths.<ref>{{cite book |title=StatPearls |vauthors=Sadiq U, Shrestha U, Guzman M |date=2021 |publisher=StatPearls Publishing |place=Treasure Island (FL) |chapter=Prevention Of Opportunistic Infections In HIV |pmid=30020717 |access-date=2021-03-09 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK513345/}}</ref>

== Causes == Immunodeficiency is characterized by the absence of or the disruption in components of the immune system such as white blood cells (e.g. lymphocytes, phagocytes, etc.). These disruptions cause a decrease in immune function and result in an overall reduction of immunity against pathogens.<ref name=":122"/>

They can be caused by a variety of factors, including:

* Pre-existing conditions such as ** HIV/AIDS infection<ref name=":03"/> ** Systemic Lupus Erythematosus (SLE) <ref>{{Cite journal |last1=Pego-Reigosa |first1=José María |last2=Nicholson |first2=Lindsay |last3=Pooley |first3=Nick |last4=Langham |first4=Sue |last5=Embleton |first5=Nina |last6=Marjenberg |first6=Zoe |last7=Barut |first7=Volkan |last8=Desta |first8=Barnabas |last9=Wang |first9=Xia |last10=Langham |first10=Julia |last11=Hammond |first11=Edward R |date=2021-01-05 |title=The risk of infections in adult patients with systemic lupus erythematosus: systematic review and meta-analysis |url=https://academic.oup.com/rheumatology/article/60/1/60/5939818 |journal=Rheumatology |volume=60 |issue=1 |pages=60–72 |doi=10.1093/rheumatology/keaa478 |pmid=33099651 |pmc=7785308 |issn=1462-0324}}</ref> ** Rheumatoid arthritis<ref>{{Cite journal |last1=Takabayashi |first1=Katsuhiko |last2=Ando |first2=Fumihiko |last3=Ikeda |first3=Kei |last4=Nakajima |first4=Hiroshi |last5=Hanaoka |first5=Hideki |last6=Suzuki |first6=Takahiro |date=2023-11-01 |title=Incidence of opportunistic infections in patients with rheumatoid arthritis treated with different molecular-targeted drugs: A population-based retrospective cohort study |url=https://academic.oup.com/mr/article/33/6/1078/6779935 |journal=Modern Rheumatology |volume=33 |issue=6 |pages=1078–1086 |doi=10.1093/mr/roac133 |pmid=36308397 |issn=1439-7595|doi-access=free }}</ref> ** Multiple Sclerosis and the treatments associated with it<ref>{{Cite journal |last1=Epstein |first1=David J |last2=Dunn |first2=Jeffrey |last3=Deresinski |first3=Stan |date=2018-08-01 |title=Infectious Complications of Multiple Sclerosis Therapies: Implications for Screening, Prophylaxis, and Management |url=https://academic.oup.com/ofid/article/5/8/ofy174/5054278 |journal=Open Forum Infectious Diseases |volume=5 |issue=8 |article-number=ofy174 |doi=10.1093/ofid/ofy174 |pmid=30094293 |pmc=6080056 |issn=2328-8957}}</ref> *Other causes include: ** Undergoing organ transplant with the use of immunosuppressant agents<ref>{{Cite web |date=2025 |title=Opportunistic Infection: Causes, Signs, and Treatment |url=https://www.medicoverhospitals.in/diseases/opportunistic-infection/ |website=Medicoverhospitals}}</ref> ** Receiving chemotherapy and other immunosuppressant drugs to combat cancer<ref>{{Cite web |title=Preventing Infections in People with Cancer |url=https://www.cancer.org/cancer/managing-cancer/side-effects/infections/preventing-infections-in-people-with-cancer.html |access-date=2025-03-09 |website=www.cancer.org |language=en}}</ref> ** Malnutrition<ref>{{Cite journal |last1=Fan |first1=Yuanyuan |last2=Yao |first2=Qianqian |last3=Liu |first3=Yufeng |last4=Jia |first4=Tiantian |last5=Zhang |first5=Junjuan |last6=Jiang |first6=Enshe |date=2022-02-23 |title=Underlying Causes and Co-existence of Malnutrition and Infections: An Exceedingly Common Death Risk in Cancer |journal=Frontiers in Nutrition |language=English |volume=9 |article-number=814095 |doi=10.3389/fnut.2022.814095 |doi-access=free |pmid=35284454 |issn=2296-861X|pmc=8906403 }}</ref> ** Genetic predisposition<ref>{{Cite web |title=New genetic disorder that causes susceptibility to opportunistic infections |url=https://www.sciencedaily.com/releases/2023/01/230121171448.htm |access-date=2025-03-09 |website=ScienceDaily |language=en}}</ref> ** Skin damage- cuts, burns, etc.<ref>{{Cite web |last=admin-infection |date=2023-12-07 |title=The Most Common Bacteria Causing Wound Infections - A Comprehensive Guide |url=https://infectioncycle.com/articles/the-most-common-bacteria-causing-wound-infections-a-comprehensive-guide |access-date=2025-03-09 |website=Infection Cycle |language=en-US}}</ref> ** Antibiotic treatment or the misuse of antibiotics leading to disruption of the normal microbiome, thus allowing some microorganisms to outcompete others and become pathogenic (e.g. disruption of intestinal microbiota may lead to ''Clostridium difficile'' infection)<ref>{{Cite web |date=2017-03-14 |title=Which Antibiotics Are Most Associated with Causing Clostridium difficile Diarrhea? |url=https://www.pharmacytimes.com/view/which-antibiotics-are-most-associated-with-causing-clostridium-difficile-diarrhea |access-date=2025-03-09 |website=Pharmacy Times |language=en}}</ref> ** Medical procedures such as surgeries, endoscopies, implants, and catheterization <ref>{{Cite web |last=admin-infection |date=2023-12-07 |title=Most Common Infection After Surgery and How to Prevent It |url=https://infectioncycle.com/articles/most-common-infection-after-surgery-and-how-to-prevent-it |access-date=2025-03-09 |website=Infection Cycle |language=en-US}}</ref><ref>{{Cite journal |last1=El Husseini |first1=Nour |last2=Carter |first2=Jared A. |last3=Lee |first3=Vincent T. |date=2024-10-21 |title=Urinary tract infections and catheter-associated urinary tract infections caused by Pseudomonas aeruginosa |journal=Microbiology and Molecular Biology Reviews |volume=88 |issue=4 |pages=e00066–22 |doi=10.1128/mmbr.00066-22 |pmc=11653733 |pmid=39431861}}</ref><ref>{{Cite web |last=practicalgast |date=2020-08-13 |title=Endoscope-Associated Infections (EAI): An Update and Future Directions |url=https://practicalgastro.com/2020/08/13/endoscope-associated-infections-eai-an-update-and-future-directions/ |access-date=2025-03-09 |website=Practical Gastro |language=en-US}}</ref><ref>{{Cite journal |last1=Arciola |first1=Carla Renata |last2=Campoccia |first2=Davide |last3=Montanaro |first3=Lucio |date=July 2018 |title=Implant infections: adhesion, biofilm formation and immune evasion |url=https://www.nature.com/articles/s41579-018-0019-y |journal=Nature Reviews Microbiology |language=en |volume=16 |issue=7 |pages=397–409 |doi=10.1038/s41579-018-0019-y |pmid=29720707 |issn=1740-1534|url-access=subscription }}</ref> ** Pregnancy due to increase susceptibility and hormonal changes<ref>{{Cite journal |last1=Kumar |first1=Manoj |last2=Saadaoui |first2=Marwa |last3=Al Khodor |first3=Souhaila |date=2022-06-08 |title=Infections and Pregnancy: Effects on Maternal and Child Health |journal=Frontiers in Cellular and Infection Microbiology |language=English |volume=12 |article-number=873253 |doi=10.3389/fcimb.2022.873253 |doi-access=free |pmid=35755838 |pmc=9217740 |issn=2235-2988}}</ref> ** Aging <ref>Kline, K., Bowdish, D., Hartland, E., & Richardson, A. (2016). Infection in an aging population. ''Current Opinion in Microbiology'', ''29'', 63–67. <nowiki>https://doi.org/10.1016/j.mib.2015.11.003</nowiki></ref> ** Leukopenia (i.e. neutropenia and lymphocytopenia)<ref>{{Cite web |title=UpToDate |url=https://www.uptodate.com/contents/infectious-causes-of-neutropenia |access-date=2025-03-09 |website=www.uptodate.com}}</ref> ** The lack of or the disruption of normal vaginal microbiota<ref name="AfricaNel20142">{{cite journal |vauthors=Africa CW, Nel J, Stemmet M |date=July 2014 |title=Anaerobes and bacterial vaginosis in pregnancy: virulence factors contributing to vaginal colonisation |journal=International Journal of Environmental Research and Public Health |volume=11 |issue=7 |pages=6979–7000 |doi=10.3390/ijerph110706979 |pmc=4113856 |pmid=25014248 |doi-access=free}}</ref><ref name="Mastro20132">{{cite journal |vauthors=Mastromarino P, Vitali B, Mosca L |date=July 2013 |title=Bacterial vaginosis: a review on clinical trials with probiotics |url=http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf |journal=The New Microbiologica |volume=36 |issue=3 |pages=229–38 |pmid=23912864 |archive-date=2015-05-18 |access-date=2015-05-11 |archive-url=https://web.archive.org/web/20150518165920/http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf }}</ref><ref>{{cite journal |vauthors=Mastromarino P, Vitali B, Mosca L |date=July 2013 |title=Bacterial vaginosis: a review on clinical trials with probiotics |url=http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf |journal=The New Microbiologica |volume=36 |issue=3 |pages=229–38 |pmid=23912864 |archive-date=2015-05-18 |access-date=2015-05-11 |archive-url=https://web.archive.org/web/20150518165920/http://www.newmicrobiologica.org/PUB/allegati_pdf/2013/3/229.pdf }}</ref><ref>{{cite journal |vauthors=Knoester M, Lashley LE, Wessels E, Oepkes D, Kuijper EJ |date=April 2011 |title=First report of Atopobium vaginae bacteremia with fetal loss after chorionic villus sampling |journal=Journal of Clinical Microbiology |volume=49 |issue=4 |pages=1684–6 |doi=10.1128/JCM.01655-10 |pmc=3122803 |pmid=21289141}}</ref>

== Prevention == Since opportunistic infections can cause severe disease, much emphasis is placed on measures to prevent infection. Such a strategy usually includes restoration of the immune system as soon as possible, avoiding exposures to infectious agents, and using antimicrobial medications ("prophylactic medications") directed against specific infections.<ref>{{cite book |url=https://books.google.com/books?id=meFwBwAAQBAJ&pg=PA688 |title=Clinical Infectious Disease |vauthors=Schlossberg D |date=2015-04-23 |publisher=Cambridge University Press |isbn=978-1-107-03891-2 |pages=688–}}</ref>

=== Restoration of immune system ===

* In patients with HIV, starting antiretroviral therapy is recommended for restoration of the immune system and reducing the incidence rate of opportunistic infections<ref>{{cite journal |display-authors=6 |vauthors=Ledergerber B, Egger M, Erard V, Weber R, Hirschel B, Furrer H, Battegay M, Vernazza P, Bernasconi E, Opravil M, Kaufmann D, Sudre P, Francioli P, Telenti A |date=December 1999 |title=AIDS-related opportunistic illnesses occurring after initiation of potent antiretroviral therapy: the Swiss HIV Cohort Study |journal=JAMA |volume=282 |issue=23 |pages=2220–6 |doi=10.1001/jama.282.23.2220 |pmid=10605973}}</ref><ref>{{cite journal |vauthors=Brooks JT, Kaplan JE, Holmes KK, Benson C, Pau A, Masur H |date=March 2009 |title=HIV-associated opportunistic infections--going, going, but not gone: the continued need for prevention and treatment guidelines |journal=Clinical Infectious Diseases |volume=48 |issue=5 |pages=609–11 |doi=10.1086/596756 |pmid=19191648 |s2cid=39742988 |doi-access=}}</ref> * In patients undergoing chemotherapy, completion of, and recovery from treatment is the primary method for immune system restoration and to prevent infection occurrence. In a select subset of high-risk patients, granulocyte colony stimulating factors (G-CSF) can be used to aid immune system recovery and infection prevention.<ref>{{cite journal |display-authors=6 |vauthors=Freifeld AG, Bow EJ, Sepkowitz KA, Boeckh MJ, Ito JI, Mullen CA, Raad II, Rolston KV, Young JA, Wingard JR |date=February 2011 |title=Clinical practice guideline for the use of antimicrobial agents in neutropenic patients with cancer: 2010 update by the infectious diseases society of america |journal=Clinical Infectious Diseases |volume=52 |issue=4 |pages=e56-93 |doi=10.1093/cid/cir073 |pmid=21258094 |doi-access=}}</ref><ref>{{cite journal |display-authors=6 |vauthors=Smith TJ, Khatcheressian J, Lyman GH, Ozer H, Armitage JO, Balducci L, Bennett CL, Cantor SB, Crawford J, Cross SJ, Demetri G, Desch CE, Pizzo PA, Schiffer CA, Schwartzberg L, Somerfield MR, Somlo G, Wade JC, Wade JL, Winn RJ, Wozniak AJ, Wolff AC |date=July 2006 |title=2006 update of recommendations for the use of white blood cell growth factors: an evidence-based clinical practice guideline |journal=Journal of Clinical Oncology |volume=24 |issue=19 |pages=3187–205 |doi=10.1200/JCO.2006.06.4451 |pmid=16682719 |doi-access=free}}</ref>

=== Avoidance of infectious exposure ===

* Ensure poultry is cooked to 165&nbsp;°F (74&nbsp;°C). Beef and pork cuts should reach an internal temperature of 145&nbsp;°F (63&nbsp;°C). Ground meat should be cooked to 160&nbsp;°F (71&nbsp;°C). Ensure juice, and dairy products are labeled as pasteurized. Eggs should be cooked until both yolks and whites are firm.<ref>{{Cite web |last=CDC |date=2025-01-31 |title=Safer Food Choices |url=https://www.cdc.gov/food-safety/foods/safer-food-choices.html |access-date=2025-04-19 |website=Food Safety |language=en-us}}</ref> * Avoid oral exposure to feces.<ref name=":022">{{Cite web |date=26 May 2020 |title=Guidelines for the prevention and treatment of opportunistic infections in adults and adolescents with HIV: recommendations from the Centers for Disease Control and Prevention, the National Institutes of Health, and the HIV Medicine Association of the Infectious Diseases Society of America |url=https://clinicalinfo.hiv.gov/sites/default/files/guidelines/documents/Adult_OI.pdf |access-date=28 November 2020 |archive-date=28 November 2020 |archive-url=https://web.archive.org/web/20201128225054/https://clinicalinfo.hiv.gov/sites/default/files/guidelines/documents/Adult_OI.pdf }}</ref> * Ensure proper steps such as regular handwashing, and use of PPE are followed for the care of farm animals who are sick, specifically those experiencing diarrhea.<ref>{{Cite web |last=CDC |date=2024-08-26 |title=Zoonotic Diseases in Rural America |url=https://www.cdc.gov/rural-health/php/public-health-strategy/public-health-strategies-for-zoonotic-diseases-in-rural-america.html |access-date=2025-04-19 |website=Rural Health |language=en-us}}</ref><ref>{{Cite web |title=Cleaning and Disinfection Tips |url=https://www.healthyagriculture.org/prevent/sanitation/cleaning-disinfection/ |access-date=2025-04-19 |website=Healthy Farms Healthy Agriculture |language=en-US}}</ref> * Ensure proper handling and handwashing with cat feces (e.g. cat litter): source of ''Toxoplasma gondii'', ''Bartonella'' spp.<ref>{{Cite web |last=misgatosingles0224ld |date=2023-09-03 |title=Should you wash your hands after scooping cat litter? |url=https://misgatosyyo.com/us/should-you-wash-your-hands-after-scooping-cat-litter/ |access-date=2025-04-19 |website=My cats and me |language=en-US}}</ref> * Avoid soil/dust in areas where there is known ''Histoplasma capsulatum'' present. If it cannot be avoided in an environment, ensure PPE is being used.<ref>{{Cite web |last=CDC |date=2024-11-21 |title=Personal Protective Equipment |url=https://www.cdc.gov/niosh/histoplasmosis/prevention/personal-protective-equipment.html |access-date=2025-04-19 |website=Histoplasmosis |language=en-us}}</ref> * Ensure reptiles and amphibians, their live food, and their waste are being handled properly and wash hands regularly after handling to prevent transmission of pathogens such as ''Salmonella''.<ref>{{Cite journal |last=Medicine |first=Center for Veterinary |date=2024-06-17 |title=Salmonella, Feeder Rodents, and Pet Reptiles and Amphibians – Tips You Should Know to Prevent Infection |url=https://www.fda.gov/animal-veterinary/animal-health-literacy/salmonella-feeder-rodents-and-pet-reptiles-and-amphibians-tips-you-should-know-prevent-infection |archive-url=https://web.archive.org/web/20190912045506/https://www.fda.gov/animal-veterinary/animal-health-literacy/salmonella-feeder-rodents-and-pet-reptiles-and-amphibians-tips-you-should-know-prevent-infection |archive-date=September 12, 2019 |journal=FDA |language=en}}</ref> * Avoid unprotected sexual intercourse with individuals that have sexually transmitted infections.<ref>{{Cite web |title=Appendix Recommendations to Help Patients Avoid Exposure to or Infection from Opportunistic Pathogens* Sexual Exposures |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5804a2.htm |access-date=2025-04-19 |website=www.cdc.gov}}</ref>

=== Prophylactic medications === Individuals at higher risk for opportunistic infections are often prescribed prophylactic medication to prevent an infection from occurring. A person's risk level for developing an opportunistic infection is approximated using the person's CD4 T-cell count and other indicators such as current medical treatments, age, and lifestyle choices. The table below provides information regarding the treatment management of common opportunistic infections.<ref name=":42">{{Cite book |last1=Dyer |first1=Mary |url=https://www.ncbi.nlm.nih.gov/books/NBK567851/ |title=Comprehensive Primary Care for Adults With HIV |last2=Kerr |first2=Christine |last3=McGowan |first3=Joseph P. |last4=Fine |first4=Steven M. |last5=Merrick |first5=Samuel T. |last6=Stevens |first6=Lyn C. |last7=Hoffmann |first7=Christopher J. |last8=Gonzalez |first8=Charles J. |date=2021 |publisher=Johns Hopkins University |series=New York State Department of Health AIDS Institute Clinical Guidelines |location=Baltimore (MD) |pmid=33625815}}</ref><ref name=":52">{{Cite web |title=European AIDS Clinical Society Guidelines |url=https://www.eacsociety.org/media/final2021eacsguidelinesv11.0_oct2021.pdf}}</ref><ref name=":62">{{Cite web |title=Table 2. Treatment of HIV-Associated Opportunistic Infections (Includes Recommendations for Acute Treatment and Secondary Prophylaxis/Chronic Suppressive/Maintenance Therapy) {{!}} NIH |url=https://clinicalinfo.hiv.gov/en/guidelines/hiv-clinical-guidelines-adult-and-adolescent-opportunistic-infections/treatment-hiv-associated-full |access-date=2023-02-20 |website=clinicalinfo.hiv.gov |language=en}}</ref><ref>{{Cite web |last=admin-infection |date=2023-12-07 |title=Opportunistic Infection - A Serious Threat to Immunocompromised Individuals |url=https://infectioncycle.com/articles/opportunistic-infection-a-serious-threat-to-immunocompromised-individuals |access-date=2025-04-19 |website=Infection Cycle |language=en-US}}</ref> {| class="wikitable" !Opportunistic infections !Indication(s) for prophylactic medications !Preferred agent(s) !When to discontinue agent(s) !Secondary prophylactic/maintenance agent(s) |- |Mycobacterium tuberculosis |Upon diagnosis of HIV, any positive screening test, or prior medical history of Mycobacterium tuberculosis. | * Rifampicin * Isoniazid * Pyridoxine * Pyrazinamide * Ethambutol |These current agents' doses/frequency will discontinue after two months. Depending on clinical presentation, maintenance agents will continue for at least four more months. | * Rifampicin, isoniazid, and pyridoxine |- |Pneumocystis jiroveci |CD4 count is less than 200 cells/mm<sup>3</sup> or less than 14%. The person has documented medical history of recurrent oropharyngeal candidiasis. | * Trimethoprim-sulfamethoxazole |This current agent doses/frequency will discontinue after 21 days. Secondary prophylactic agent dose/frequency will continue until the CD4 count is above 200 cells/mm<sup>3</sup> and the HIV viral load is undetectable for at least three months while taking antiretroviral therapy. | * Trimethoprim-sulfamethoxazole |- |Toxoplasma gondii |CD4 count is less than 100 cells/mm<sup>3</sup> or less than 14%, and the person has a positive serology for Toxoplasma gondii. | * Trimethoprim-sulfamethoxazole |This agent will discontinue after six weeks. Secondary prophylactic medications will continue until the CD4 count is above 200 cells/mm<sup>3</sup> and HIV viral load is undetectable for at least six months while taking antiretroviral therapy. | * Sulfadiazine, pyrimethamine, and folinic acid |- |Mycobacterium avium complex disease |CD4 count is less than 50 cells/mm<sup>3</sup> and has a detectable viral load while taking antiretroviral therapy. | * Clarithromycin and ethambutol * Rifabutin may be added depending on clinical presentation. |These agent(s) will discontinue after 12 months only if the person does not have any symptoms that will be concerning for persistent Mycobacterium avium complex disease and their CD4 count is above 100 cells/mm<sup>3</sup>, and while their HIV viral load is undetectable for at least six months while taking antiretroviral therapy. |N/A |}

=== Alternative prevention === Alternative agents can be used instead of the preferred agents. These alternative agents may be used due to an individual's allergies, availability, or clinical presentation. The alternative agents are listed in the table below.<ref name=":42"/><ref name=":5">{{Cite web |title=European AIDS Clinical Society Guidelines |url=https://www.eacsociety.org/media/final2021eacsguidelinesv11.0_oct2021.pdf}}</ref><ref name=":62"/> {| class="wikitable" !Opportunistic infections !Alternative agent(s) |- |Mycobacterium tuberculosis | * Rifabutin |- |Pneumocystis jiroveci | * Dapsone * Atovaquone * Pentamidine |- |Toxoplasma gondii | * Dapsone, pyrimethamine, and folinic acid * Atovaquone, pyrimethamine, and folinic acid |- |Mycobacterium avium complex disease | * Azithromycin and ethambutol |}

==Treatment== Due to the prevention techniques used with HIV patients, such as prophylactic medications, opportunistic infections in HIV patients have decreased in number over the past few decades. In some circumstances, where individuals are not aware they have HIV and they develop an opportunistic infection, they may be prescribed antivirals, antibiotics, or antifungals. After the infection has cleared, and to prevent it from coming back, they may be recommended to stay on that medication as well as it being coupled with another medication to ensure drug efficiency.<ref>Opportunistic infections. (2015). ''Rheumatology''. [https://www.neaetc.org/files/attachment/attachment/5976/EP%20-%20Opportunistic%20Infections%202021-05.pdf https://doi.org/10.1093/rheumatology/kev074]</ref>

{{commons category|Opportunistic infections}} {{clear}}

== References == {{Reflist}}

== External links == {{Medical resources | DiseasesDB = | ICD10 = | ICD9 = | ICDO = | OMIM = | MedlinePlus = | eMedicineSubj = | eMedicineTopic = | MeshID = D009894 }} {{Concepts in infectious disease}}

Category:Infectious diseases Category:Immunology Category:Immune system disorders