How HIV is spread
- Sexual contact. The virus may enter the body through a tear in the lining of the rectum, vagina, urethra, or mouth. Most cases of HIV are spread this way.
- Infected blood. HIV can be spread when a person:
HIV may be spread more easily in the early stage of infection and again later, when symptoms of HIV-related illness develop.
How HIV is not spread
The virus doesn't survive well outside the body. So HIV cannot be spread through casual contact with an infected person, such as by sharing drinking glasses, by casual kissing, or by coming into contact with the person's sweat or urine.
It is now extremely rare in the United States for HIV to be transmitted by blood transfusions or organ transplants.
The window period
After you've been infected, it can take 2 weeks to 6 months for your body to start making HIV antibodies.
This means that during this time you could have a negative HIV test, even though you have been infected and can spread the virus to others.
This is commonly called the "window period," or seroconversion period.
Stages of HIV
Most people go through the following stages after being infected with HIV:
Initial stage (stage 1)
The first stage of HIV infection is defined by the U.S. Centers for Disease Control and Prevention (CDC) as a CD4+ cell count of at least 500 cells per microliter or a percentage of CD4+ cells at least 29% of all lymphocytes. People in this stage don't have any symptoms.4
Chronic stage (stage 2)
The second stage of HIV infection is defined by the CDC as a CD4+ cell count of 200 to 499 or a percentage of CD4+ cells of 14% to 28%.4 It may take years for HIV symptoms to develop during this stage. But even though no symptoms are present, the virus is making copies of itself (multiplying) in the body during this time.
HIV multiplies so quickly that the immune system can't destroy the virus. After years of fighting HIV, the immune system starts to weaken.
AIDS (stage 3)
AIDS occurs when the CD4+ cell counts drop below 200, the percentage of CD4+ cells is less than 14%, or an AIDS-defining condition is present.5
If HIV isn't treated, most people get AIDS within 10 to 12 years after the initial infection. With treatment for HIV, the progression to AIDS may be delayed or prevented.
After your immune system starts to weaken, you are more likely to get certain infections or illnesses, called opportunistic infections. Examples include some types of pneumonia or cancer that are more common when you have a weakened immune system.
A small number of people who are infected with HIV are rapid progressors. They develop AIDS within a few years if they don't get treatment. It is not known why the infection progresses faster in these people.
Left untreated, AIDS is often fatal within 18 to 24 months after it develops. Death may occur sooner in people who rapidly progress through the stages of HIV or in young children.
Nonprogressors and people who are HIV-resistant
A few people have HIV that doesn't 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. These people are said to be HIV-resistant.