What is an Opportunistic Infection?

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.

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OIs are caused by a variety of germs (viruses, bacteria, fungi, and parasites). OI-causing germs spread in a variety of ways, for example in the air, in body fluids, or in contaminated food or water. Here are examples of some of the most common OIs in people with HIV in the United States: 

• Herpes simplex virus (HSV) infection—a viral infection that can cause painful cold sores in or around the mouth, or painful ulcers on or around the genitals or anus

• 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

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Why do people with HIV get OIs?

Once a person has 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.

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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.

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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.

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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).