The Human Immunodeficiency Virus and Its Transmission

CDC National AIDS Clearinghouse

Research has revealed a great deal of valuable medical, scientific, and public health information about the human immunodeficiency virus (HIV) and acquired immmunodeficiency syndrome (AIDS). The ways in which HIV can be transmitted have been clearly identified. Unfortunately, some widely dispersed information does not reflect the conclusions of scientific findings. The Centers for Disease Control and Prevention (CDC) provides the following information to help correct a few commonly held misperceptions about HIV.


HIV is spread by sexual contact with an infected person, by needle-sharing among injecting drug users, 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 gets into the worker's bloodstream through an 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 five patients. Investigations have been completed involving more than 15,000 patients of 32 HIV-infected doctors 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 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 promptly and 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 below, Saliva, Tears, and Sweat.) In order 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 under precisely controlled and limited laboratory conditions, CDC studies have showned that drying of even these high concentrations of HIV reduces the number of infectious viruses 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 alarmed people unnecessarily. Results from laboratory studies should not be used to determine specific personal risk of infection because 1) the amount of virus studied is not found in human specimens or anyplace else in nature, and 2) no one has been identified with HIV due to contact with an environmental surface; Additionally, since 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, it does not spread or maintain infectiousness outside its host.

Households, Offices, and Workplaces

Studies of thousands of households where families have lived with and cared for AIDS patients have found no instances of nonsexual transmission, despite the sharing of kitchen, laundry, and bathroom facilities, meals, eating utensils, and drinking cups and glasses. If HIV is not transmitted in these settings, where repeated and prolonged contact occurs, transmission is even less likely in other settings, such as schools and offices.

Similarly, 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 illinesses (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.


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-mouthed 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.

Saliva, Tears, and Sweat

HIV has been found in saliva and tears in only minute 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.


From the onset of the HIV epidemic, there has been concern about transmission of the virus by biting and blood-sucking 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 indiciate that when an insect bites a person, it does not inject its own or a previous victim's blood into the new victim. Rather, it injects saliva. 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, therefore, cannot 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.

There is also no reason to fear that a biting or blood-sucking insect, such as a mosquito, could transmit HIV from one person to another through HIV-infected blood left on its mouth parts. Two factors combine to make infection by this route extremely unlikely-- 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.

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 contain natural pores and are therefore not recommended for disease prevention. 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. Proper use should include the following:

  • Put on the condom as soon as erection occurs and before any sexual contact (vaginal, anal, or oral).
  • Leave space at the tip of the condom.
  • Use only water-based lubricants. (Oil-based lubricants can weaken the condom.)
  • Hold the condom firmly to keep it from slipping off and withdraw from the partner immediately after ejaculation.

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. Each latex condom manufactured in the United States is tested for defects, including holes, before it is packaged, and several studies 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 can provide up to 98-99 percent protection against pregnancy and most sexually transmitted diseases, including HIV infection, but only if they are used consistently and correctly.

For more detailed information about condoms, see CDC's fact sheet, The Role of Condoms in Preventing HIV Infection and Other Sexually Transmitted Diseases."

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. In addition to research on the virus and its transmission, the PHS program to prevent the spread of HIV/AIDS includes counseling, testing, and education. Through these programs, individuals who have engaged in high-risk behaviors can receive voluntary HIV-antibody testing for themselves and their partners, and those found to be infected can be counseled regarding preventive services and treatment options, as well as how to prevent transmission to others.

For more information:

            CDC National AIDS Hotline:    1-800-342-AIDS
                  Spanish:                1-800-344-7432
                  Deaf:                   1-800-243-7889
            CDC National AIDS Clearinghouse
            P.O. Box 6003
            Rockville, MD 20849-6003

[email protected] (Mon Jul 11 21:07:55 1994)