What Is the Difference between HIV and AIDS?

When a person is infected with the human immunodeficiency virus (HIV) we say that he or she is "HIV positive," or "has HIV." A person who has HIV is classified as having AIDS if one of two things happens:

  1. the CD4 count has dropped below 200/cc, or
  2. an HIV-related infection or HIV-related cancer develops.

A CD4 count below 200 cells/cc is called AIDS by definition. A patient may have 200 CD4 cells or less and feel very healthy, but he or she still has AIDS by definition. The reason 200 was chosen as the cut-off for AIDS is that most HIV-related infections and cancers occur in patients with less than 200 CD4 cells.

How Do People Get HIV Infection?

This is very straightforward: people get HIV through close contact with HIV-infected body fluids like blood, semen, or vaginal secretions. In practical terms 99 percent of HIV infections result from having unprotected sex with a person who has HIV, from sharing injection drugs with an HIV-infected person, or from being born to an HIV-positive woman who is not taking antiretroviral therapy.

Virtually all forms of sexual contact that exchange body fluids, except kissing, carry a high risk for spreading HIV. While the risk for contracting HIV through recipient anal or vaginal intercourse is higher than for oral sex, HIV can be passed to either person engaging in oral sex.

There is a myth in the United States that HIV is a "gay disease" and that heterosexuals are not at risk. That is completely false. Worldwide, the number one cause for HIV infection is heterosexual sex. Numbers of new HIV infections in the United States from heterosexual sex have been increasing since the late 1980s. Anyone who engages in oral, vaginal, or anal sex without the use of a condom can be infected with HIV if their sexual partner is HIV positive. Many people who are HIV positive look very healthy.

Sharing HIV contaminated injection equipment (e.g., needles, syringes) is another common cause for new HIV infections. In fact, in some regions of the United States (e.g., the Northeast), abuse of injectable drugs has been the number one cause of new cases since 1987.

People who use injectable drugs should never share syringes or needles. Abuse of alcohol and non-injectable drugs also increases the risk for HIV infection by lowering people's inhibitions and increasing the trading of sex for drugs or money.

There are many drug treatment programs that provide treatment for substance abuse. For information regarding drug treatment in a specific area of the United States, go to The Substance Abuse & Mental Health Services Administration website.

Antiretroviral therapy has caused a substantial decline in the number of cases of HIV transmission from mother to baby in North America and Western Europe. Scientific studies have shown that HIV-positive women who are on combination antiretroviral therapy and whose virus is undetectable, have a 0–2 percent risk for passing the virus to their unborn babies. This is a dramatic improvement from the 25–30 percent risk if the mother is not taking antiretroviral therapy, and the 8 percent risk if she takes AZT alone.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 30 Nov 2000

Last Modified: 12 Aug 2015