Opportunistic infection

Opportunistic infection
Classification and external resources
MeSH D009894

An opportunistic infection is an infection caused by pathogens (bacteria, viruses, fungi, or protozoa) that take advantage of an opportunity not normally available, such as a host with a weakened immune system, an altered microbiota (such as a disrupted gut flora), or breached integumentary barriers. Many of these pathogens do not cause disease in a healthy host that has a normal immune system. However, a compromised immune system, a penetrating injury, or a lack of competition from normal commensals presents an opportunity for the pathogen to infect.


Immunodeficiency or immunosuppression can be caused by:

The lack of or the disruption of normal vaginal flora allows the proliferation of opportunistic microorganisms and will cause the opportunistic infection - bacterial vaginosis.[1][2][3][4]

Types of infections

Further information: Immunodeficiency

A partial listing of opportunistic organisms includes:

Prophylaxis (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.

Restoration of Immune System

Infectious Exposures to Avoid[9]

Prophylactic Medications

Individuals at higher risk are often prescribed prophylactic medication to prevent an infection from occurring. A patient's risk level for developing an opportunistic infection is approximated using the patient's CD4 T-cell count and sometimes other markers of susceptibility. Common prophylaxis treatments include the following:[10]

Infection When to Give Prophylaxis Agent
Pneumocystis jirovecii CD4 < 200 cells/mm3 or oropharyngeal candidasis (thrush) TMP-SMX
Toxoplasma gondii CD4 < 100 cells/mm3 and positive Toxoplasma gondii IgG immunoassay TMP-SMX
Mycobacterium avium complex CD4 < 50 Azithromycin


Treatment depends on the type of opportunistic infection, but usually involves different antibiotics.

Veterinary treatment

Opportunistic infections caused by Feline Leukemia Virus and Feline immunodeficiency virus retroviral infections can be treated with Lymphocyte T-Cell Immune Modulator.

Wikimedia Commons has media related to Opportunistic pathogens.


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  2. Mastromarino, Paola; Vitali, Beatrice; Mosca, Luciana (2013). "Bacterial vaginosis: a review on clinical trials with probiotics" (PDF). New Microbiologica. 36: 229–238. PMID 23912864.
  3. Mastromarino, Paola; Vitali, Beatrice; Mosca, Luciana (2013). "Bacterial vaginosis: a review on clinical trials with probiotics" (PDF). New Microbiologica. 36: 229–238. PMID 23912864.
  4. Knoester, M.; Lashley, L. E. E. L. O.; Wessels, E.; Oepkes, D.; Kuijper, E. J. (2011). "First Report of Atopobium vaginae Bacteremia with Fetal Loss after Chorionic Villus Sampling". Journal of Clinical Microbiology. 49 (4): 1684–1686. doi:10.1128/JCM.01655-10. ISSN 0095-1137.
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  6. Brooks, John T.; Kaplan, Jonathan E.; Holmes, King K.; Benson, Constance; Pau, Alice; Masur, Henry (Mar 1, 2009). "HIV-associated opportunistic infections--going, going, but not gone: the continued need for prevention and treatment guidelines". Clinical Infectious Diseases. 48 (5): 609–611. doi:10.1086/596756. ISSN 1537-6591. PMID 19191648. Retrieved 2015-05-09.
  7. Freifeld, Alison G.; Bow, Eric J.; Sepkowitz, Kent A.; Boeckh, Michael J.; Ito, James I.; Mullen, Craig A.; Raad, Issam I.; Rolston, Kenneth V.; Young, Jo-Anne H. (Feb 15, 2011). "Clinical practice guideline for the use of antimicrobial agents in neutropenic patients with cancer: 2010 update by the infectious diseases society of america". Clinical Infectious Diseases. 52 (4): e56–93. doi:10.1093/cid/cir073. ISSN 1537-6591. PMID 21258094. Retrieved 2015-05-09.
  8. Smith, Thomas J.; Khatcheressian, James; Lyman, Gary H.; Ozer, Howard; Armitage, James O.; Balducci, Lodovico; Bennett, Charles L.; Cantor, Scott B.; Crawford, Jeffrey (Jul 1, 2006). "2006 update of recommendations for the use of white blood cell growth factors: an evidence-based clinical practice guideline". Journal of Clinical Oncology. 24 (19): 3187–3205. doi:10.1200/JCO.2006.06.4451. ISSN 1527-7755. PMID 16682719. Retrieved 2015-05-09.
  9. "AIDSinfo: Recommendations to Help HIV-infected Patients Avoid Exposure to, or Infection from, Opportunistic Pathogens". 5/7/2013. Retrieved 2015-05-09. Check date values in: |date= (help)
  10. "AIDSinfo: Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents" (PDF). 2013-06-17. Retrieved 2015-05-09.
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