Opportunistic infections and AIDS-related cancers

HIV weakens your immune system, leaving you vulnerable to certain infections and cancers. The infections are called "opportunistic" because they take the opportunity to attack you when your immune system is weak. The cancers are called "AIDS related" because they appear mostly in people who have advanced, later-stage HIV infection, known as AIDS.

Most people who die of AIDS do not die from the virus itself. They die from opportunistic infections (or "OIs"). Often, people are infected with the OI long before they become infected with HIV. Their functioning immune system keeps the OI under control, so they don't have any symptoms of the infection. Once HIV damages their immune system enough, the OI becomes uncontrolled and makes them sick. In fact, many HIV-negative people have opportunistic infections but don't know about it because their immune system keeps the infections in check.

If you have HIV, you can take antibiotics to prevent the OI from causing disease. For example, one common opportunistic infection is Pneumocystis jiroveci pneumonia (also called PCP). Most people already have the microbe that causes PCP in their body, but it doesn't make them sick. An HIV-positive person, however, may need to take antibiotics to keep from getting very sick.

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