What Happens

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. About 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.

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 treatment after it is born. Treatment of a baby shortly after birth greatly reduces the chance that the baby will die from the HIV infection.⁴

Ways HIV cannot be spread

HIV does not survive well outside the body. So HIV cannot be spread through casual contact with an infected person, such as by sharing drinking glasses or by casual kissing. 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. Tests at 6, 12, and 24 weeks can be done to be sure you are not infected.

After you become infected with HIV, your blood, semen, or vaginal fluids should always be considered infectious, even if you receive treatment for the HIV infection.

Stages of HIV

Most people go through the following stages after being infected with HIV if the infection is not treated:

• Acute retroviral syndrome, which may have symptoms similar to mononucleosis. This often develops within a few days of infection, but may occur several weeks after the person is infected.
• HIV without symptoms (asymptomatic). It may take years for HIV symptoms to develop. But even though no symptoms are present, the virus is multiplying (or making copies of itself) in the body during this time. HIV multiplies so quickly that the immune system cannot destroy the virus. After years of fighting HIV, the immune system starts to weaken.
• HIV with symptoms (symptomatic). After your immune system starts to weaken, you are more likely to develop certain infections or illnesses, such as some types of pneumonia or cancer that are more common in people who have a weakened immune system.
• AIDS, which occurs during the last stage of infection with HIV. If HIV goes untreated, AIDS develops in most people within 10 to 12 years after the initial infection. With treatment for HIV, the progression to AIDS may be delayed or prevented.

A small number of people who are infected with HIV are rapid progressors. They develop AIDS within a few years if they do not receive treatment. It is not known why the infection progresses faster in these people.

Nonprogressors and HIV-resistant

A few people have HIV that does not progress to more severe symptoms or disease. They are referred to as nonprogressors.

A small number of people never become infected with HIV despite years of exposure to the virus. For example, they may have repeated, unprotected sex with an infected person. These people are said to be HIV-resistant.