What Is an Opportunistic Infection (OI)?
Opportunistic infections (OIs) are infections that occur more often or are more severe in people with weakened immune systems than in people with healthy immune systems. People with weakened immune systems include people living with HIV or people receiving chemotherapy.
OIs are caused by a variety of germs (viruses, bacteria, fungi, and parasites). OI-causing germs can spread in the air; in saliva, semen, blood, urine, or feces (poop); or in contaminated food and water. Here are examples of common HIV-related OIs:
- Herpes simplex virus 1 (HSV-1) infection -- a viral infection that can cause lesions (sores) on the lips, mouth, and face
- Salmonella infection -- a bacterial infection that affects the intestines (the gut)
- Candidiasis (or thrush) -- a fungal infection of the mouth, bronchi, trachea, lungs, esophagus, or vagina
- Toxoplasmosis -- a parasitic infection that can affect the brain
Why Do People With HIV Get OIs?
Once a person is infected with HIV, the virus begins to multiply and to damage the immune system. A weakened immune system makes it harder for the body to fight off HIV-related OIs.
HIV medicines prevent HIV from damaging the immune system. But if a person with HIV does not take HIV medicines, HIV infection can gradually destroy the immune system and advance to AIDS. Many OIs, for example, certain forms of pneumonia and tuberculosis (TB), are considered AIDS-defining conditions. AIDS-defining conditions are infections and cancers that are life-threatening in people with HIV.
Are OIs Common in People With HIV?
Before HIV medicines were available to treat HIV infection, OIs were the main cause of illness and death in people with HIV. HIV medicines are now widely used in the United States so fewer people with HIV get OIs. By preventing HIV from damaging the immune system, HIV medicines reduce the risk of OIs.
However, OIs are still a problem for many people with HIV. Some people with HIV get OIs for the following reasons:
- About 15% of people who have HIV don't know that they are infected. An OI may be the first sign that they have HIV.
- Some people who know they have HIV aren't getting treatment with HIV medicines. Without HIV treatment, they are more likely to get an OI.
- Some people may be taking HIV medicines, but the medicines aren't controlling their HIV. Poorly controlled HIV can be due to many factors, including lack of health care, poor medication adherence, or incomplete absorption of HIV medicines. People with poorly controlled HIV have an increased risk of getting an OI.
What Can People With HIV Do to Prevent Getting an OI?
For people with HIV, the best protection against OIs is to take HIV medicines every day.
People living with HIV can also take the following steps to reduce their risk of getting an OI.
Avoid contact with the germs that can cause OIs.
The germs that can cause OIs can spread in the feces of people and animals. To prevent OIs, don't touch animal feces. Wash your hands with warm, soapy water after touching anything soiled with human feces, for example, a dirty diaper.
Ask your health care provider about other ways to avoid the germs that can cause OIs.
Be careful about what you eat and drink.
Food and water can be contaminated with OI-causing germs. To be safe, don't eat or drink the following foods:
- Raw or undercooked eggs, for example, in homemade mayonnaise or uncooked cookie dough
- Raw or undercooked poultry, meat, and seafood (especially raw shellfish)
- Unpasteurized milk, cheeses, and fruit juices
- Raw seed sprouts, such as alfalfa sprouts or mung bean sprouts
Only drink tap water, filtered water, or bottled water. Don't drink water directly from a lake or river. For more information, read the AIDSinfo HIV and Nutrition and Food Safety fact sheet.
If you are visiting a foreign country, avoid eating food and drinking water that could make you sick. Before you travel, read this CDC fact sheet on travel abroad for people living with HIV.
Vaccines are products that protect people from diseases such as chicken pox, influenza (flu), and polio. Some vaccines can prevent HIV-related OIs. For example, people with HIV can get vaccinated to prevent pneumonia.
To learn more, read the AIDSinfo fact sheet on HIV and Immunizations.
Can OIs Be Treated?
There are many medicines to treat HIV-related OIs, including antiviral, antibiotic, and antifungal drugs. The type of medicine used depends on the OI.
Once an OI is successfully treated, a person may continue to use the same medicine or an additional medicine to prevent the OI from reoccurring (coming back).
The AIDSinfo Drug Database includes information on many of the medicines used to prevent and treat OIs.
This fact sheet is based on information from the following sources:
- From CDC: Opportunistic Infections
- From CDC, the National Institutes of Health, and the HIV Medicine Association of the Infectious Diseases Society of America: Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents: Introduction and Appendix A. Recommendations to Help HIV-infected Patients Avoid Exposure to, or Infection from, Opportunistic Pathogens
[Note from TheBody: This article was created by AIDSinfo, who last updated it on June 14, 2018. We have cross-posted it with their permission.]