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2.1. How is HIV transmitted?


This article is from the AIDS FAQ, by Dan Greening with numerous contributions by others.

2.1. How is HIV transmitted?

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) providest he 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

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.

Insects - see Question 2.4


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