Opportunistic infection

Opportunistic infection

Opportunistic infection
Classification and external resources
MeSH D009894

An opportunistic infection is an infection caused by bacterial, viral, fungal, or protozoan pathogens that take advantage of a host with a weakened immune system or an altered microbiota (such as a disrupted gut flora). Many of these pathogens do not cause disease in a healthy host that has a normal immune system. A compromised immune system, however, presents an "opportunity" for the pathogen to infect.


  • Causes 1
  • Types of infections 2
  • Prophylaxis (Prevention) 3
    • Restoration of Immune System 3.1
    • Infectious Exposures to Avoid 3.2
    • Prophylactic Medications 3.3
  • Treatment 4
  • Veterinary treatment 5
  • References 6


Immunodeficiency or immunosuppression can be caused by:

The lack of or the disruption of bacterial vaginosis.[1][2][3][4]

Types of infections

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

  • In patients with HIV, starting antiretroviral therapy is especially important for restoration of the immune system and reduces the incidence of all opportunistic infections[5][6]
  • In patients undergoing chemotherapy, completion of and recovery from treatment is the primary method for immune system restoration. In a select subset of high risk patients, granulocyte colony stimulating factors (G-CSF) can be used to aid immune system recovery.[7][8]

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.


  1. ^ Africa, Charlene; Nel, Janske; Stemmet, Megan (2014). "Anaerobes and Bacterial Vaginosis in Pregnancy: Virulence Factors Contributing to Vaginal Colonisation". International Journal of Environmental Research and Public Health 11 (7): 6979–7000.  
  2. ^ Mastromarino, Paola; Vitali, Beatrice; Mosca, Luciana (2013). "Bacterial vaginosis: a review on clinical trials with probiotics" (PDF). New Microbiologica 36: 229–238.  
  3. ^ Mastromarino, Paola; Vitali, Beatrice; Mosca, Luciana (2013). "Bacterial vaginosis: a review on clinical trials with probiotics" (PDF). New Microbiologica 36: 229–238.  
  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.  
  5. ^ Ledergerber, B.; Egger, M.; Erard, V.; Weber, R.; Hirschel, B.; Furrer, H.; Battegay, M.; Vernazza, P.; Bernasconi, E. (Dec 15, 1999). "AIDS-related opportunistic illnesses occurring after initiation of potent antiretroviral therapy: the Swiss HIV Cohort Study". JAMA 282 (23): 2220–2226.  
  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: An Official Publication of the Infectious Diseases Society of America 48 (5): 609–611.  
  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: An Official Publication of the Infectious Diseases Society of America 52 (4): e56–93.  
  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: Official Journal of the American Society of Clinical Oncology 24 (19): 3187–3205.  
  9. ^ "AIDSinfo: Recommendations to Help HIV-infected Patients Avoid Exposure to, or Infection from, Opportunistic Pathogens". 5/7/2013. Retrieved 2015-05-09. 
  10. ^ "AIDSinfo: Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents" (PDF). 2013-06-17. Retrieved 2015-05-09.