When was HIV discovered and how is it diagnosed?
In 1981, homosexual men with symptoms that now are considered diagnostic of AIDS were first described in Los Angeles and New York. The men had an unusual type of lung infection (pneumonia) called Pneumocystis carinii pneumonia (PCP) and rare skin tumors called Kaposi's sarcoma. The patients were noted to have severe suppression of a specific type of immune blood cells, called CD4 cells. These cells, often referred to as T cells, help the body fight infections. Shortly thereafter, this disease was recognized throughout the United States, Western Europe, and Africa. In 1983, researchers in the United States and France described the virus that causes AIDS, now known as HIV. In 1985, a blood test became available that measures antibodies to HIV, which thereby detects the body's immune response to the HIV. This blood test remains the best method for diagnosing HIV infection. Recently, tests have become available to look for these same antibodies in the saliva and urine.
How is HIV spread (transmitted)?
HIV is present in the blood and genital secretions of virtually all infected individuals, regardless of whether or not they have symptoms. The spread of HIV can occur when these secretions come in contact with tissues such as those lining the vagina, anal area, mouth, or eyes (the mucosal membranes), or with a break in the skin, such as from a cut or puncture by a needle. The most common ways in which HIV is spreading throughout the world include sexual contact, needle sharing, and transmission from infected mothers to their newborns during pregnancy, labor (the delivery process), or breast- feeding. (See the section below on treatment during pregnancy for a discussion on reducing the risk of transmission to the newborn.)
Sexual transmission of HIV has been described from men to men, men to women, women to men, and women to women through vaginal, anal, and oral sex. The best way to avoid sexual transmission is abstinence from sex until it is certain that both partners in a monogamous relationship are not HIV-infected. Because the HIV antibody test can take up to 6 months to turn positive, both partners would need to test negative 6 months after their last potential exposure to HIV. If abstinence is out of the question, the next best method is the use of latex barriers. This involves placing a condom on the penis as soon as an erection is achieved in order to avoid exposure to pre- ejaculatory and ejaculatory fluids that contain infectious HIV. Concerning oral sex, condoms should be used for fellatio (oral contact with the penis) and latex barriers (dental dams) for cunnilingus (oral contact with the vaginal area). A dental dam is any piece of latex that prevents vaginal secretions from coming in direct contact with the mouth. Although such dams occasionally can be purchased, they are most often created by cutting a square piece of latex from a condom.
The spread of HIV by exposure to infected blood usually results from sharing needles, as in those used for illicit drugs. HIV also can be spread by sharing needles for anabolic steroids taken to increase muscle, tattooing, and body piercing. To prevent the spread of HIV, as well as other diseases including hepatitis, needles should never be shared. At the beginning of the HIV epidemic, many individuals acquired HIV infection from blood transfusions or blood products, such as those used for hemophiliacs. Currently, however, because blood is tested for antibodies to HIV before transfusing it, the risk of acquiring HIV from a blood transfusion in the United States is extremely small and is considered insignificant.
There is little evidence that HIV can be transferred by casual exposure, as might occur in a household setting. For example, unless there are open sores or blood in the mouth, kissing is generally considered not to be a risk factor for transmitting HIV. This is because saliva, in contrast to genital secretions, has been shown to contain very little of the virus. Still, theoretical risks are associated with the sharing of toothbrushes and shaving razors because they can cause bleeding. Consequently, these items should not be shared with infected persons. Similarly, without sexual exposure or direct contact with blood, there is little if any risk of HIV contagion in the workplace or classroom.
What happens after an exposure to an HIV- infected person?
The risk of HIV transmission occurring after any potential exposure to bodily fluids is poorly defined. The highest risk sexual activity, however, is thought to be anal intercourse without a condom. In this case, the risk of infection may be as high as 3% to 5% for each exposure. The risk probably is less for vaginal intercourse without a condom and even less for oral sex without a latex barrier. Despite the fact that no single sexual exposure carries a high risk of contagion, HIV infection can occur after any isolated sexual event. Thus, people must always be diligent in protecting themselves from potential infection.