The Human Immunodeficiency Virus and Its Transmission

Research has revealed a great deal of valuable medical, scientific, and public health information about the human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS). The ways in which HIV can be transmitted have been clearly identified. Unfortunately, some materials that conflict with the scientific findings have been widely dispersed. The Centers for Disease Control and Prevention (CDC) provides the following information to correct a few misperceptions about HIV.

Transmission

HIV is spread by sexual contact with an infected person, by sharing needles and/or syringes (primarily for drug injection) with someone who is infected, or, less commonly (and now very rarely in countries where blood is screened for HIV antibodies), through transfusions of infected blood or blood clotting factors. Babies born to HIV-infected women may become infected before or during birth, or through breast-feeding after birth.

In the health-care setting, workers have been infected with HIV after being stuck with needles containing HIV-infected blood, or less frequently, after infected blood contacts the worker's open cut or splashes into a mucous membrane (e.g., eyes or inside of the nose). There has been only one demonstrated instance of patients being infected by a health-care worker; this involved HIV transmission from an infected dentist to six patients. Investigations have been completed involving more than 22,000 patients of 63 HIV-infected physicians, surgeons, and dentists, and no other cases of this type of transmission have been identified.

Some people fear that HIV might be transmitted in other ways; however, no scientific evidence to support any of these fears has been found. If HIV were being transmitted through other routes ( for example, through air, food, water, animals, or insects), the pattern of reported AIDS cases would be much different from what has been observed, and cases would be occurring much more frequently in persons who report no identified risk for infection. All reported cases suggesting new or potentially unknown routes of transmission are thoroughly investigated by state and local health departments with the assistance, guidance, and laboratory support from CDC; no additional routes of transmission have been recorded, despite a national sentinel system designed to detect just such an occurrence.

The following paragraphs specifically address some of the more common misperceptions about HIV transmission.

HIV in the Environment

Scientists and medical authorities agree that HIV does not survive well in the environment, making the possibility of environmental transmission remote. HIV is found in varying concentrations or amounts in blood, semen, vaginal fluid, breast milk, saliva, and tears. (See page 3, Saliva, Tears, and Sweat.) To obtain data on the survival of HIV, laboratory studies have required the use of artificially high concentrations of laboratory-grown virus. Although these unnatural concentrations of HIV can be kept alive for days or even weeks under precisely controlled and limited laboratory conditions, CDC studies have shown that drying of even these high concentrations of HIV reduces the amount of infectious virus by 90 to 99 percent within several hours. Since the HIV concentrations used in laboratory studies are much higher than those actually found in blood or other specimens, drying of HIV-infected human blood or other body fluids reduces the theoretical risk of environmental transmission to that which has been observed - essentially zero. Incorrect interpretation of conclusions drawn from laboratory studies have unnecessarily alarmed some people.

Results from laboratory studies should not be used to access specific personal risk of infection because 1) the amount of virus studied is not found in human specimens or elsewhere in nature, and 2) no one has been identified as infected with HIV due to contact with an environmental surface. Additionally, HIV is unable to reproduce outside its living host (unlike many bacteria or fungi, which may do so under suitable conditions), except under laboratory conditions, therefore, it does not spread or maintain infectiousness outside its host.

Households and Other Settings

Although HIV has been transmitted between family members in a household setting, this type of transmission is very rare. These transmissions are believed to have resulted from contact between skin or mucous membranes and infected blood. To prevent even such rare occurrences, precautions, as described in previously published guidelines, should be taken in all settings- including the home-to prevent exposures to the blood of persons who are HIV infected, at risk for HIV infection, or whose infection and risk status are unknown. For example, gloves should be worn during contact with blood or other body fluids that could possibly contain blood, such as urine, feces, or vomit. Cuts, sore, or breaks on both the care giver's and patient's exposed skin should be covered with bandages. Hands and other parts of the body should be washed immediately after contact with blood or other body fluids, and surfaces soiled with blood contact, such as sharing razors and toothbrushes, should be avoided. Needles and other sharp instruments should be used only when medically necessary and handled according to recommendations for healthcare settings. (Do not put caps back on needles by hand or remove needles from syringes. Dispose of needles in puncture-proof containers out of the reach of children and visitors.)

There is no known risk of HIV transmission to co-workers, clients, or consumers from contact in industries such as food-service establishments (see information on survival of HIV in the environment). Food-service workers known to be infected with HIV need not be restricted from work unless they have other infections or illnesses (such as diarrhea or hepatitis A) for which any food-service worker, regardless of HIV infection status, should be restricted. The Public Health Service recommends that all food-service workers follow recommended standards and practices of good personal hygiene and food sanitation.

In 1985, CDC issued routine precautions that all personal-service workers (e.g., hairdressers, barbers, cosmetologists, massage therapists) should follow, even though there is no evidence of transmission from a personal-service worker to a client or vice versa. Instruments that are intended to penetrate the skin (e.g., tattooing and acupuncture needles, ear piercing devices) should be used once and disposed of or thoroughly cleaned and sterilized. Instruments not intended to penetrate the skin but which may become contaminated with blood (e.g., razors) should be used for only one client and disposed of or thoroughly cleaned and disinfected after each use. Personal-service workers can use the same cleaning procedures that are recommended for heatlh-care institutions.

Kissing

Casual contact through closed-mouth or "social" kissing is not a risk for transmission of HIV. Because of the theoretical potential for contact with blood during "French" or open-mouth kissing, CDC recommends against engaging in this activity with an infected person. However, no case of AIDS reported to CDC can be attributed to transmission through any kind of kissing.

Biting

Recently, a state health department conducted an investigation of an incident that suggested blood-to-blood transmission of HIV by a human bite. There have been other reports in the medical literature in which HIV appeared to have been transmitted by a bite. Severe trauma with extensive tissue tearing and damage and presence of blood were reported in each of these instances. Biting is not a common way of transmitting HIV. In fact, there are numerous reports of bites that did not result in HIV infection.

Saliva, Tears and Sweat

HIV has Been found in saliva and tears in very low quantities from some AIDS patients. It is important to understand that finding a small amount of HIV in a body fluid does not necessarily mean that HIV can be transmitted by that body fluid. HIV has not been recovered from the sweat of HIV-infected persons. Contact with saliva, tears, or sweat has never been shown to result in transmission of HIV.

Insects

From the onset of the HIV epidemic, there has been concern about transmission of the virus by biting and bloodsucking insects. However, studies conducted by researchers at CDC and elsewhere have shown no evidence of HIV transmission through insects - even in areas where there are many cases of AIDS and large populations of insects such as mosquitoes. Lack of such outbreaks, despite intense efforts to detect them, supports the conclusion that HIV is not transmitted by insects.

The results of experiments and observations of insect biting behavior indicate that when an insect bites a person, it does not inject its own or a previously bitten person's or animal's blood into the next person bitten. Rather, it injects saliva, which acts as a lubricant or anticoagulant so the insect can feed efficiently. Such diseases as yellow fever and malaria are transmitted through the saliva of specific species of mosquitoes. However, HIV lives for only a short time inside an insect and, unlike organisms that are transmitted via insect bites, HIV does not reproduce (and, does not survive) in insects. Thus, even if the virus enters a mosquito or another sucking or biting insect, the insect does not become infected and cannot transmit HIV to the next human it feeds on or bites. HIV is not found in insect feces.

There is also no reason to fear that a biting or bloodsucking insect, such as a mosquito, could transmit HIV from one person to another through HIV-infected blood left on its mouth parts. Two factors serve to explain why this is so - first, infected people do not have constant, high levels of HIV in their bloodstreams and, second, insect mouth parts do not retain large amounts of blood on their surfaces. Further, scientists who study insects have determined that biting insects normally do not travel from one person to the next immediately after ingesting blood. Rather, they fly to a resting place to digest this blood meal.

Effectiveness of Condoms

The proper and consistent use of latex condoms when engaging in sexual intercourse - vaginal, anal, or oral - can greatly reduce a person's risk of acquiring or transmitting sexually transmitted diseases, including HIV infection.

Under laboratory conditions, viruses occasionally have been shown to pass through natural membrane ("skin" or lambskin) condoms, which may contain natural pores and are therefore not recommended for disease prevention (they are documented to be effective for contraception). On the other hand, laboratory studies have consistently demonstrated that latex condoms provide a highly effective mechanical barrier to HIV.

In order for condoms to provide maximum protection, they must be used consistently (every time) and correctly. Incorrect use contributes to the possibility that the condom could leak or break.

When condoms are used reliably, they have been shown to prevent pregnancy up to 98 percent of the time among couples using them as their only method of contraception. Similarly, numerous studies among sexually active people have demonstrated that a properly used latex condom provides a high degree of protection against a variety of sexually transmitted diseases, including HIV infection.

Condoms are classified as medical devices and are regulated by the Food and Drug Administration. Condom manufacturers in the United States test each latex condom for defects, including holes, before it is packaged. Several studies of correct and consistent condom use clearly show that condom breakage rates in this country are less than 2 percent. Even when condoms do break, one study showed that more than half of such breaks occurred prior to ejaculation.

Latex condoms are highly effective in preventing pregnancy and most sexually transmitted diseases, including HIV infection, but only if they are used consistently and correctly.

The Public Health Service Response

The U.S. Public Health Service is committed to providing the scientific community and the public with accurate and objective information about HIV infection and AIDS. It is vital that clear information on HIV infection and AIDS be readily available to help prevent further transmission of the virus and to allay fears and prejudices caused by misinformation.

For more information:

CDC National AIDS Hotline:
1-800-342-AIDS (2437)

Spanish:
1-800-344-SIDA (7432)

Deaf:
1-800-243-7889

CDC National AIDS Clearinghouse
P.O. BOX 6003
Rockville, MD 20849-6003

Click here to go to the CDC's Web Site

SOURCE:
CDC