Opportunistic infection

{{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.{{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}}

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

• 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.{{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}}{{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}}
• Legionella pneumophila is a bacterium that causes Legionnaire's disease, a respiratory infection.{{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 }}{{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 | pages = 486 | date = 2016-04-08 | pmid = 27092135 | pmc = 4824771 | doi = 10.3389/fmicb.2016.00486 | doi-access = free }}
• 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.{{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 }}{{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 }}
• Mycobacterium tuberculosis is a species of bacteria that causes tuberculosis, a respiratory infection.{{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 }}
• 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.{{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}}{{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}}
• Salmonella is a genus of bacteria that is known to cause gastrointestinal infections causing an inflammatory response accompanied with fever and diarrhea.{{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=}}{{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}}
• 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.{{cite journal | vauthors = Jenul C, Horswill AR | title = Regulation of Staphylococcus aureus Virulence | journal = Microbiology Spectrum | volume = 7 | issue = 2 | date = April 2019 | pmid = 30953424 | pmc = 6452892 | doi = 10.1128/microbiolspec.GPP3-0031-2018 }}{{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 | pages = 72 | date = March 2016 | pmid = 26999200 | pmc = 4810217 | doi = 10.3390/toxins8030072 | doi-access = free }}
• Streptococcus pneumoniae is a bacterium that causes respiratory infections as well as meningitis and bacteremia.{{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 |pages=98 |doi=10.3389/fcimb.2016.00098 |pmc=5030221 |pmid=27709102 |doi-access=free}}{{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}}
• 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.{{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 | pages = 104609 | date = December 2020 | pmid = 33147506 | doi = 10.1016/j.meegid.2020.104609 | doi-access = free | bibcode = 2020InfGE..8604609J }}{{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 }}

• Aspergillus is a fungus, commonly associated with respiratory infection.{{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 | pmid = 31722890 | pmc = 6860006 | doi = 10.1128/CMR.00140-18 }}{{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 }}
• 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.{{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}}{{cite journal |vauthors=Erdogan A, Rao SS |date=April 2015 |title=Small intestinal fungal overgrowth |journal=Current Gastroenterology Reports |volume=17 |issue=4 |pages=16 |doi=10.1007/s11894-015-0436-2 |pmid=25786900 |s2cid=3098136}}{{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}}
• Coccidioides immitis is a fungus known for causing coccidioidomycosis, more commonly known as Valley Fever.{{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 }}
• Cryptococcus neoformans is a fungus that causes cryptococcosis, which can lead to pulmonary infection as well as nervous system infections, like meningitis.{{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 | pages = a019760 | date = July 2014 | pmid = 24985132 | pmc = 4066639 | doi = 10.1101/cshperspect.a019760 }}{{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 }}
• 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.{{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 }}{{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 }}
• Pseudogymnoascus destructans (formerly known as Geomyces destructans) is a fungus that causes white-nose syndrome in bats.{{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 }}
• Microsporidia is a group of fungi that infect species across the animal kingdom, one species of which can cause microsporidiosis in immunocompromised human hosts.{{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 }}
• Pneumocystis jirovecii (formerly known as Pneumocystis carinii) is a fungus that causes pneumocystis pneumonia, a respiratory infection.{{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 }}

• Cryptosporidium is a protozoan that causes the condition Cryptosporidiosis. This condition affects the gastrointestinal tract.{{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}}{{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 }}
• Toxoplasma gondii is a protozoan, known for causing toxoplasmosis which is known to lead to impairment of the brain. {{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 |pages=e1006351 |doi=10.1371/journal.ppat.1006351 |pmc=5519211 |pmid=28727854 |doi-access=free |veditors=Gubbels MJ}}{{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}}{{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}}

• Cytomegalovirus is considered a member of the human herpesvirus family and is most frequently associated with respiratory infection.{{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}}{{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 |pages=3865 |doi=10.3390/ijms20163865 |pmc=6719013 |pmid=31398860 |doi-access=free}}{{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.}}
• Human polyomavirus 2 (also known as JC virus) is known to cause progressive multifocal leukoencephalopathy (PML) which affects the central nervous system.{{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 |pages=1073274817729901 |doi=10.1177/1073274817729901 |pmc=5937251 |pmid=28975841}}{{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}}{{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}}
• Human herpesvirus 8 (also known as Kaposi sarcoma-associated herpesvirus) is a virus associated with Kaposi sarcoma, a type of skin cancer.{{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=}}{{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 |pages=9 |doi=10.1038/s41572-019-0060-9 |pmc=6685213 |pmid=30705286}}

Human Immunodeficiency Virus is a virus that targets the CD4 cells (a type of white blood cell) within the body's immune system. 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.{{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 |pages=979 |doi=10.1186/s12889-025-22096-6 |doi-access=free |issn=1471-2458 |pmc=11905675 |pmid=40075339}} HIV infection can lead to progressively worsening immunodeficiency, a condition ideal for the development of opportunistic infection.{{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}}{{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}} 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.{{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}}{{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 |pages=a017871 |doi=10.1101/cshperspect.a017871 |pmc=4484961 |pmid=25722472}}{{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 |pages=CD005647 |doi=10.1002/14651858.CD005647.pub3 |pmc=6513250 |pmid=30045416 |collaboration=Cochrane Infectious Diseases Group}} Kaposi's sarcoma, a virally associated cancer, and non-Hodgkin's lymphoma are two types of cancers that are generally defined as AIDS malignancies.{{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}} 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.{{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=http://www.ncbi.nlm.nih.gov/books/NBK513345/}}

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.{{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=http://www.ncbi.nlm.nih.gov/books/NBK500027/}}

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

• Pre-existing conditions such as
• HIV/AIDS infection{{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}}
• Systemic Lupus Erythematosus (SLE) {{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}}
• Rheumatoid arthritis{{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 }}
• Multiple Sclerosis and the treatments associated with it{{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 |pages=ofy174 |doi=10.1093/ofid/ofy174 |pmid=30094293 |pmc=6080056 |issn=2328-8957}}

• Other causes include:
• Undergoing organ transplant with the use of immunosuppressant agents{{Cite web |date=2025 |title=Opportunistic Infection: Causes, Signs, and Treatment |url=https://www.medicoverhospitals.in/diseases/opportunistic-infection/ |website=Medicoverhospitals}}
• Receiving chemotherapy and other immunosuppressant drugs to combat cancer{{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}}
• Malnutrition{{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 |doi=10.3389/fnut.2022.814095 |doi-access=free |pmid=35284454 |issn=2296-861X|pmc=8906403 }}
• Genetic predisposition{{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}}
• Skin damage- cuts, burns, etc. {{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}}
• 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){{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}}
• Medical procedures such as surgeries, endoscopies, implants, and catheterization {{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}}{{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|pmc-embargo-date=October 21, 2025 }}{{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}}{{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}}
• Pregnancy due to increase susceptibility and hormonal changes{{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 |doi=10.3389/fcimb.2022.873253 |doi-access=free |pmid=35755838 |pmc=9217740 |issn=2235-2988}}
• Aging Kline, K., Bowdish, D., Hartland, E., & Richardson, A. (2016). Infection in an aging population. Current Opinion in Microbiology, 29, 63–67. https://doi.org/10.1016/j.mib.2015.11.003
• Leukopenia (i.e. neutropenia and lymphocytopenia){{Cite web |title=UpToDate |url=https://www.uptodate.com/contents/infectious-causes-of-neutropenia |access-date=2025-03-09 |website=www.uptodate.com}}
• The lack of or the disruption of normal vaginal microbiota{{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}}{{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}}{{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}}{{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}}

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.{{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–}}

• In patients with HIV, starting antiretroviral therapy is recommended for restoration of the immune system and reducing the incidence rate of opportunistic infections{{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}}{{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=}}
• 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.{{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=}}{{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}}

• Ensure poultry is cooked to 165°F (74°C). Beef and pork cuts should reach an internal temperature of 145°F (63°C). Ground meat should be cooked to 160°F (71°C). Ensure juice, and dairy products are labeled as pasteurized. Eggs should be cooked until both yolks and whites are firm. {{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}}
• Avoid oral exposure to feces.{{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}}
• 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. {{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}}{{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}}
• Ensure proper handling and handwashing with cat feces (e.g. cat litter): source of Toxoplasma gondii, Bartonella spp.{{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}}
• 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. {{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}}
• 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.{{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 |journal=FDA |language=en}}
• Avoid unprotected sexual intercourse with individuals that have sexually transmitted infections. {{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}}

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.{{Cite book |last1=Dyer |first1=Mary |url=http://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}}{{Cite web |title=European AIDS Clinical Society Guidelines |url=https://www.eacsociety.org/media/final2021eacsguidelinesv11.0_oct2021.pdf}}{{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}}{{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}}

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.{{Cite book |last1=Dyer |first1=Mary |url=http://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}}{{Cite web |title=European AIDS Clinical Society Guidelines |url=https://www.eacsociety.org/media/final2021eacsguidelinesv11.0_oct2021.pdf}}{{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}}

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. 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]

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{{Concepts in infectious disease}}

Category:Infectious diseases

Category:Immunology

Category:Immune system disorders