Acute HIV infection is caused by the human immunodeficiency virus (HIV), a virus that gradually destroys the immune system.

Primary or acute HIV infection occurs 2 - 4 weeks after infection with the human immunodeficiency virus (HIV). The virus is spread by:

• Sexual contact
• Contaminated blood transfusions and blood products
• Injection drug use with contaminated needles and syringes
• Passing through the placenta from an infected, pregnant mother to the unborn baby
• Breastfeeding (rarely)

After someone is infected with HIV, blood tests can detect antibodies to the virus, even if they never had any symptoms of their infection. This is called HIV seroconversion (converting from HIV negative to HIV positive by blood testing), and usually occurs within 3 months of exposure, but on rare occasions can by delayed up to a year after infection.

Following the initial infection, there may be no further evidence of illness for the next 10 years. This stage is called asymptomatic HIV infection.

Acute HIV infection can, but does not always, progress to early symptomatic HIV infection and to advanced HIV disease (AIDS). However, the vast majority of patients do ultimately progress to AIDS. To date there are a small number of people who have tested positive for HIV, but later no longer test positive and have no signs of disease. Although this is relatively rare, it provides evidence that the human body may be capable of removing the disease. These people are being carefully watched and studied.

HIV has spread throughout the world. Higher numbers of people with the disease are found in large metropolitan centers, inner cities, and among certain populations with high-risk behaviors.