|
TRANSMISSION OF AIDS
How is AIDS transmitted?
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 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.
Transmission
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.
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 shown
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
- the amount of virus studied is not found in human specimens or anyplace
else in nature
- no one has been identified with HIV due to contact with an environmental
surface;
- 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 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, sores, or breaks on both the care givers 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 bodily fluids, and
surfaces soiled with blood should be disinfected appropriately.
Practices that increase the likelihood of blood contact, such as sharing of
razors and toothbrushes, should be avoided. Needles and other sharp instruments
should be used only when medically necessary and handled according to
recommendations for health-care 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.
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 health-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-mouthed kissing, CDC recommends
against engaging in this activity with an infected person. There has been a
case of oral mucosa HIV transmission reported recently.
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 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
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
indicate 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
- infected people do not have constant, high levels of HIV in their
bloodstreams
- 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. Several studies clearly show that condom breakage rates in this
country are less than 2 percent and 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.
References
- CDC. Condoms for prevention of sexually transmitted diseases. MMWR
1988;37:133-7.
- Cates W, Stone KM. Family planning, sexually transmitted diseases, and
contraceptive choice: a literature update. Fam Plann Perspect 1992;24:75-84.
- Weller SC. A meta-analysis of condom effectiveness in reducing sexually
transmitted HIV. Soc Sci Med 1993;1635-44.
- DeVincenzi I, European Study Group on Heterosexual Transmission of HIV.
Heterosexual transmission of HIV in a European cohort of couples (Abstractno.
WS-CO2-1). Vol 1. IXth International Conference on AIDS/IVth STD World
Congress. Berlin, June 9, 1993:83.
- Saracco A, Musicco M, Nicolosi A, et al. Man-to-woman sexual transmission
of HIV: longitudinal study of 343 steady partners of infected men. J Acquir
Immune Defic Syndr 1993;6:497-502.
- Carey RF, Herman WA, Retta SM, Rinaldi JE, Herman BA, Athey TW.
Effectiveness of latex condoms as a barrier to human immunodeficiency
virus-sized particles under conditions of simulated use. Sex Transm Dis
1992;19:230-4.
- Trussell JE, Warner DL, Hatcher R. Condom performance during vaginal
intercourse: comparison of Trojan-Enz (TM) and Tactylon (TM) condoms.
Contraception 1992;45:11-9.
- Jones EF, Forrest JD. Contraceptive failure rates based on the 1988 NSFG.
Fam Plann Perspect 1992;24:12-9.
- Trussell J, Hatcher RA, Cates W, Stewart FH, Kost K. Contraceptive failure
in the United States: an update. Stud Fam Plann 1990;21:51-4.
- Roper WL, Peterson HB, Curran JW. Commentary: condoms and HIV/STD
prevention -- clarifying the message. Am J Public Health 1993;83:501-3.
|
