HIV frequently is spread among injection drug users by the sharing of needles or syringes contaminated with minute quantities of blood of someone infected with the virus. However, transmission from patient to health-care worker or vice-versa via accidental sticks with contaminated needles or other medical instruments is rare.

     Women can transmit HIV to their fetuses during pregnancy or birth. Approximately one-quarter to one-third of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus. If the drug AZT is taken during pregnancy, the chance of transmitting HIV to the baby is reduced significantly. If AZT treatment of mothers is combined with cesarean sectioning to deliver infants, infection rates can be reduced to 1 percent.

     Although researchers have detected HIV in the saliva of infected individuals, no evidence exists that the virus is spread by contact with saliva. Laboratory studies reveal that saliva has natural compounds that inhibit the infectiousness of HIV. Studies of people infected with HIV have found no evidence that the virus is spread to others through saliva such as by kissing. No one knows, however, the risk of infection from so-called "deep" kissing, involving the exchange of large amounts of saliva, or by oral intercourse. Scientists also have found no evidence that HIV is spread through sweat, tears, urine or feces.

     Studies of families of HIV-infected people have shown clearly that HIV is not spread through casual contact such as the sharing of food utensils, towels and bedding, swimming pools, telephones or toilet seats. HIV is not spread by biting insects such as mosquitoes or bedbugs.

    HIV can infect anyone who practices risky behaviors such as:

     More persistent or severe symptoms may not surface for a decade or more after HIV first enters the body in adults, or within two years in children born with HIV infection. This period of "asymptomatic" infection is highly variable. Some people may begin to have symptoms in as soon as a few months, whereas others may be symptom-free for more than 10 years. During the asymptomatic period, however, HIV is actively multiplying, infecting and killing cells of the immune system. HIV's effect is seen most obviously in a decline in the blood levels of CD4+ T cells (also called T4 cells) -- the immune system's key infection fighters. The virus initially disables or destroys these cells without causing symptoms.

     As the immune system deteriorates, a variety of complications begins to surface. One of the first such symptoms experienced by many people infected with HIV is large lymph nodes or "swollen glands" that may be enlarged for more than three months. Other symptoms often experienced months to years before the onset of AIDS include a lack of energy, weight loss, frequent fevers and sweats, persistent or frequent yeast infections (oral or vaginal), persistent skin rashes or flaky skin, pelvic inflammatory disease that does not respond to treatment, or short-term memory loss.

     Some people develop frequent and severe herpes infections that cause mouth, genital or anal sores, or a painful nerve disease known as shingles. Children may have delayed development or failure to thrive.

     In 1993, CDC revised its definition of AIDS to include all HIV-infected people who have fewer than 200 CD4+ T cells. (Healthy adults usually have CD4+ T-cell counts of 1,000 or more.) In addition, the definition includes 26 clinical conditions that affect people with advanced HIV disease. Most AIDS-defining conditions are opportunistic infections, which rarely cause harm in healthy individuals. In people with AIDS, however, these infections are often severe and sometimes fatal because the immune system is so ravaged by HIV that the body cannot fight off certain bacteria, viruses and other microbes.

     Opportunistic infections common in people with AIDS cause such symptoms as coughing, shortness of breath, seizures, mental symptoms such as confusion and forgetfulness, severe and persistent diarrhea, fever, vision loss, severe headaches, weight loss, extreme fatigue, nausea, vomiting, lack of coordination, coma, abdominal cramps, or difficult or painful swallowing.

     Although children with AIDS are susceptible to the same opportunistic infections as adults with the disease, they also experience severe forms of the bacterial infections to which children are especially prone, such as conjunctivitis (pink eye), ear infections and tonsillitis.

     People with AIDS are particularly prone to developing various cancers, especially those caused by viruses such as Kaposi's sarcoma and cervical cancer, or cancers of the immune system known as lymphomas. These cancers are usually more aggressive and difficult to treat in people with AIDS. Hallmarks of Kaposi's sarcoma in light-skinned people are round brown, reddish or purple spots that develop in the skin or in the mouth. In dark-skinned people, the spots are more pigmented.

     During the course of HIV infection, most people experience a gradual decline in the number of CD4+ T cells, although some individuals may have abrupt and dramatic drops in their CD4+ T-cell counts. A person with CD4+ T cells above 200 may experience some of the early symptoms of HIV disease. Others may have no symptoms even though their CD4+ T-cell count is below 200.

     Many people are so debilitated by the symptoms of AIDS that they are unable to hold steady employment or do household chores. Other people with AIDS may experience phases of intense life-threatening illness followed by phases of normal functioning.

     A small number of people (less than 50) initially infected with HIV 10 or more years ago have not developed symptoms of AIDS. Scientists are trying to determine what factors may account for their lack of progression to AIDS, such as particular characteristics of their immune systems, or whether they were infected with a less aggressive strain of the virus or if their genetic make-up may protect them from the effects of HIV. Scientists hope that understanding the body's natural method of control may lead to ideas for protective HIV vaccines and use of vaccines to prevent disease progression.

     Two different types of antibody tests, ELISA and Western Blot, are used to diagnose HIV infection. If a person is highly likely to be infected with HIV and yet both tests are negative, a doctor may test for the presence of HIV itself in the blood. The person also may be told to repeat antibody testing at a later date, when antibodies to HIV are more likely to have developed.

     The Food and Drug Administration has approved a number of drugs for the treatment of HIV infection. The first group of drugs used to treat HIV infection, called nucleoside analog reverse transcriptase inhibitors (NRTIs), interrupt an early stage of virus replication. Included in this class of drugs are zidovudine (also known as AZT), zalcitabine (ddC), didanosine (ddI), stavudine (D4T), lamivudine (3TC) and abacavir succinate. These drugs may slow the spread of HIV in the body and delay the onset of opportunistic infections. Importantly, they do not prevent transmission of HIV to other individuals. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) such as delavirdine, nevirapine and efavirenz are also available for use in combination with other antiretroviral drugs.

     A third class of anti-HIV drugs, called protease inhibitors, interrupts virus replication at a later step in its life cycle. They include ritonavir, saquinivir, indinavir and nelfinavir. Because HIV can become resistant to each class of drugs, combination treatment using both is necessary to effectively suppress the virus.

     Currently available antiretroviral drugs do not cure people of HIV infection or AIDS, however, and they all have side effects that can be severe. AZT may cause a depletion of red or white blood cells, especially when taken in the later stages of the disease. If the loss of blood cells is severe, treatment with AZT must be stopped. DdI can cause an inflammation of the pancreas and painful nerve damage.

     The most common side effects associated with protease inhibitors include nausea, diarrhea and other gastrointestinal symptoms. In addition, protease inhibitors can interact with other drugs resulting in serious side effects. Investigators also recently have reported cases of abnormal redistribution of body fat among some individuals receiving protease inhibitors.

     A number of drugs are available to help treat opportunistic infections to which people with HIV are especially prone. These drugs include foscarnet and ganciclovir, used to treat cytomegalovirus eye infections, fluconazole to treat yeast and other fungal infections, and TMP/SMX or pentamidine to treat Pneumocystis carinii pneumonia (PCP).

     In addition to antiretroviral therapy, adults with HIV whose CD4+ T-cell counts drop below 200 are given treatment to prevent the occurrence of PCP, which is one of the most common and deadly opportunistic infections associated with HIV. Children are given PCP preventive therapy when their CD4+ T-cell counts drop to levels considered below normal for their age group. Regardless of their CD4+ T-cell counts, HIV-infected children and adults who have survived an episode of PCP are given drugs for the rest of their lives to prevent a recurrence of the pneumonia.

     Although some laboratory evidence shows that spermicides can kill HIV organisms, in clinical trials, researchers have not found that these products can prevent HIV.

For information about studies of new HIV therapies, call the AIDS Clinical Trials Information Service:

1-800-TRIALS-A
1-800-243-7012 (TDD/Deaf Access)

For federally approved treatment guidelines on HIV/AIDS, call the HIV/AIDS Treatment Information Service: