There are two types of HIV:

• HIV-1, which causes almost all the cases of AIDS worldwide.
• HIV-2, which causes an AIDS-like illness. HIV-2 infection is uncommon in the United States.

How the disease is spread

HIV is spread when blood, semen, or vaginal fluids from an infected person enter another person's body, usually through:

• Sexual contact. The virus may enter the body through a tear in the lining of the rectum, vagina, urethra, or mouth. Between 75% and 80% of all cases of HIV are transmitted by sexual contact.³
• Infected blood. HIV can be spread when a person:
  • Shares needles, syringes, cookers, cotton, cocaine spoons, or eyedroppers used for injecting drugs or steroids.
  • Is accidentally stuck with a needle or other sharp item that is contaminated with HIV.

It is now extremely rare in the United States for HIV to be transmitted by blood transfusions or organ transplants. Blood and organ donors are screened for risk factors. All donated blood and organs are screened for HIV.

Health care workers are no longer considered to be at high risk of exposure to HIV. Policies are in place in health facilities that require protection from accidental exposure. Workers must properly dispose of sharp objects and wear protective gloves, gowns, and eye and face protection. These measures have been effective in protecting health care workers from HIV.

Spread of HIV to babies

A woman who is infected with HIV can spread the virus to her baby during pregnancy, delivery, or breast-feeding.

• Most children younger than 13 years who have HIV were infected with the virus by their mothers.
• The risk of a woman spreading HIV to her baby can be greatly reduced if she is on medicine that reduces her viral load (HIV RNA) to undetectable levels during pregnancy, if she receives AZT (ZDV) before the baby is born, and if she does not breast-feed her baby. The baby should also receive ZDV after it is born.

Ways HIV cannot be spread

HIV does not survive well outside the body. Therefore, HIV cannot be spread through casual contact-such as sharing drinking glasses or by casual kissing-with an infected person. HIV is not transmitted through contact with an infected person's saliva, sweat, tears, urine, or feces, or through insect bites.

Contagious and incubation period

The incubation period-the time between when a person is first infected with HIV and when early symptoms develop-may be a few days to several weeks.

It can take as little as 2 weeks or as long as 6 months from the time you become infected with HIV for the antibodies to be detected in your blood. This is commonly called the "window period," or seroconversion period. During the window period, you are contagious and can spread the virus to others. If you think you have been infected with HIV but you test negative for it, you should be tested again 6 months later.