While many viruses can be controlled by the immune system, HIV targets and infects the same immune system cells that are supposed to protect us from illnesses. These are a type of white blood cell called CD4 cells. HIV takes over CD4 cells and turns them into virus factories that produce thousands of viral copies. As the virus grows, it damages or kills CD4 cells, weakening the immune system.

When the immune system loses too many CD4 cells, you are less able to fight off infection and can develop serious illnesses, cancers, and neurological problems. These are called opportunistic infections (OIs) because they take advantage of the body's weakened defenses. OIs can lead to hospitalization and disability, and are responsible for most of the deaths in people with AIDS.

The Centers for Disease Control and Prevention (CDC) defines an HIV+ person with a CD4 cell count of 200 or less as having AIDS. The CDC has also developed a list of more than 20 opportunistic infections that are considered AIDS-defining conditions. If you have HIV and one or more of these OIs, you have AIDS.

Even if your CD4 cell count goes back above 200 or an OI is successfully treated, you will still have a diagnosis of AIDS. This does not necessarily mean you are sick or will get sick in the future. It is just the system used by the government to count the number of people who have been diagnosed with AIDS.

The best way to prevent OIs is to keep your immune system as strong as possible by taking HIV drugs before your CD4 cell count falls too low (below 200). This allows the immune system to do its job of controlling infections.

If your CD4 cells do fall below 200, taking appropriate medication at certain CD4 cell levels can prevent many OIs from developing. Taking medication to prevent disease is called “prophylaxis.”

Effective treatment options are available in most cases if you do develop an OI. After you recover, you may still need to receive on-going maintenance treatment to prevent the OI from coming back.

You may be able to stop prophylaxis or maintenance treatments if your CD4 cell count goes up. You should not discontinue any treatment without discussing it first with your doctor.

There are certain sex differences in OIs:

• Men are eight times more likely than women to develop Kaposi's sarcoma (KS)
• Women are more likely than men to develop bacterial pneumonia
• Women may have higher rates of herpes simplex infections than men

Dysplasia is a pre-cancerous condition in the female reproductive system, It is often more severe and difficult to treat in HIV+ women than in HIV-negative women. Untreated dysplasia can lead to cervical cancer, a life-threatening illness and an AIDS-defining condition.

It is important for HIV+ women to have regular Pap smears and gynecological exams to identify infection, dysplasia, or cancer. In addition, HIV+ women should have regular lab tests and appointments with their HIV provider to monitor their health. On-going medical care allows for the effective prevention or early diagnosis and treatment of OIs.

View the chart below or download a PDF version (70KB).

1		Bartlett, J.G. & Gallant, J.E. (2002). Management of opportunistic infections and other complications of HIV infection. Medical Management of HIV Infection, Online Edition: Retrieved June 2003 from http://www.hopkins-aids.edu/publications/book/book_toc.html.
2		Castro, K.G. et. al. (1993). 1993 revised classification system for HIV infection and expanded surveillance case definition for AIDS among adolescents and adults. CDC Morbidity and Mortality Weekly Report.
3		United States Public Health Service & Infectious Diseases Society of America. (2001). 2001 USPHS/IDSA guidelines for the prevention of opportunistic infections in persons infected with human immunodeficiency virus: Retrieved June 2003 from http://aidsinfo.nih.gov/guidelines/op_infections/OI_112801.html.