The involuntary weight loss of 10 percent of baseline body weight plus either chronic diarrhoea (two loose stools per day for more than 30 days) or chronic weakness and documented fever (for 30 days or more, intermittent or constant) in the absence of a concurrent illness or condition other than HIV infection that would explain the findings.

A laboratory test for specific antibodies to confirm repeatedly reactive results on the HIV ELISA or EIA tests. In the U.S. Western Blot is the validation test used most often for confirmation of these other tests.

Any of the various white blood cells that together make up the immune system. Neutrophils, lymphocytes, and monocytes are all leukocytes.

A method for categorizing HIV-infected individuals according to the severity of their disease. Four stages are defined, and individuals are always categorized according to the most severe symptom they have experienced thus far. Stages 1 and 2 are relatively asymptomatic. Illnesses defining of stage 3 include oral infections, recurrent vulvovaginal candidiasis and diarrhoea. Stage 4 corresponds to clinical AIDS, and includes conditions such as Kaposi’s sarcoma, extrapulmonary tuberculosis and cryptococcal meningitis.

The original type of HIV, unchanged by having developed any resistance to antiretroviral drugs. Also, 1. the prevalent type of a virus in the host population before genetic manipulation or mutation; 2. virus that is isolated from a host as opposed to one grown in a laboratory culture.

The time between the initial (first) infection and the development of detectable HIV antibodies. During this time the antibody test will be falsely negative. The test will be negative even though the person is actually infected with HIV. Antibodies are usually detected after about 6 weeks following infection. Some individuals may take 12 weeks before the antibodies are detected. Even though the test is negative during early infection, the person is able to pass on the virus to others during this window period.

Time from infection with HIV until antibodies are detected.