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Go to the HIV and its Transmission Menu How is AIDS transmitted?
From the 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 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
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
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.
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 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 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 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 (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 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
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-- 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:
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 information about condoms, see "How Effective Are Condoms?" Update: Barrier Protection against Sexual Diseases
From the CDC National AIDS Clearinghouse
1993
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: 1-800-342-2437 Spanish: 1-800-344-7432 Deaf: 1-800-243-7889 CDC National AIDS Clearinghouse P.O. Box 6003 Rockville, MD 20849-6003
Go to the What is HIV Disease & AIDS Menu
Go to the HIV and its Transmission Menu How Effective Are Condoms?
Although refraining from intercourse with infected partners remains the
most effective strategy for preventing human immunodeficiency virus (HIV)
infection and other sexually transmitted diseases (STDs), the Public
Health Service also has recommended condom use as part of its strategy.
Since CDC summarized the effectiveness of condom use in preventing HIV
infection and other STDs in 1988
(ref 1), additional information has become
available, and the Food and Drug Administration has approved a
polyurethane "female condom." This report updates laboratory and
epidemiologic information regarding the effectiveness of condoms in
preventing HIV infection and other STDs and the role of spermicides used
adjunctively with condoms. (Note 1)
Two reviews summarizing the use of latex condoms among serodiscordant
heterosexual couples (i.e., in which one partner is HIV positive and the
other HIV negative) indicated that using latex condoms substantially
reduces the risk for HIV transmission
(ref 2,
ref 3). In addition, two subsequent
studies of serodiscordant couples confirmed this finding and emphasized
the importance of consistent (i.e., use of a condom with each act of
intercourse) and correct condom use
(ref 4,
ref 5).
In one study of serodiscordant
couples, none of 123 partners who used condoms consistently seroconverted;
in comparison, 12 (10%) of 122 seronegative partners who used condoms
inconsistently became infected
(4). In another study of serodiscordant
couples (with seronegative female partners of HIV-infected men), three
(2%) of 171 consistent condom users seroconverted, compared with eight
(15%) of 55 inconsistent condom users. When person-years at risk were
considered, the rate for HIV transmission among couples reporting
consistent condom use was 1.1 per 100 person-years of observation,
compared with 9.7 among inconsistent users
(5).
Condom use reduces the
risk for gonorrhea, herpes simplex virus (HSV) infection, genital ulcers,
and pelvic inflammatory disease
(2)). In addition, intact latex condoms
provide a continuous mechanical barrier to HIV, HSV, hepatitis B virus
(HBV), Chlamydia trachomatis, and Neisseria gonorrhoeae
(2)). A recent laboratory study
(ref 6) indicated that latex condoms are an effective
mechanical barrier to fluid containing HIV-sized particles. Three
prospective studies in developed countries indicated that condoms are
unlikely to break or slip during proper use. Reported breakage rates in
the studies were 2% or less for vaginal or anal intercourse (ref 7).
Laboratory studies indicate
that the female condom (Reality [TM](Note 2)) -- a lubricated
polyurethane sheath with a ring on each end that is inserted into the
vagina -- is an effective mechanical barrier to viruses, including HIV. No
clinical studies have been completed to define protection from HIV
infection or other STDs. However, an evaluation of the female condom's
effectiveness in pregnancy prevention was conducted during a 6-month
period for 147 women in the United States. The estimated 12-month failure
rate for pregnancy prevention among the 147 women was 26%. Of the 86 women
who used this condom consistently and correctly, the estimated 12-month
failure rate was 11%.
Laboratory studies indicate that nonoxynol-9, a
nonionic surfactant used as a spermicide, inactivates HIV and other
sexually transmitted pathogens. In a cohort study among women, vaginal use
of nonoxynol-9 without condoms reduced risk for gonorrhea by 89%; in
another cohort study among women, vaginal use of nonoxynol-9 without
condoms reduced risk for gonorrhea by 24% and chlamydial infection by 22%
(2). No reports indicate that nonoxynol-9 used alone without condoms is
effective for preventing sexual transmission of HIV. Furthermore, one
randomized controlled trial among prostitutes in Kenya found no protection
against HIV infection with use of a vaginal sponge containing a high dose
of nonoxynol-9 (2). No studies have shown that nonoxynol-9 used with a
condom increases the protection provided by condom use alone against HIV
infection.
Reported by: Food and Drug Administration. Center for Population Research,
National Institute of Child Health and Human Development, National
Institutes of Health. Office of the Associate Director for HIV/AIDS; Div
of Reproductive Health, National Center for Chronic Disease Prevention and
Health Promotion; Div of Sexually Transmitted Diseases and HIV Prevention,
National Center for Prevention Svcs; Div of HIV/AIDS, National Center for
Infectious Diseases, CDC.
Editorial Note: This report indicates that latex condoms are highly
effective for preventing HIV infection and other STDs when used
consistently and correctly. Condom availability is essential in assuring
consistent use. Men and women relying on condoms for prevention of HIV
infection or other STDs should carry condoms or have them readily
available.
Correct use of a latex condom requires 1) using a new condom with each act
of intercourse; 2) carefully handling the condom to avoid damaging it with
fingernails, teeth, or other sharp objects; 3) putting on the condom after
the penis is erect and before any genital contact with the partner; 4)
ensuring no air is trapped in the tip of the condom; 5) ensuring adequate
lubrication during intercourse, possibly requiring use of exogenous
lubricants; 6) using only water-based lubricants (e.g., K-Y jelly
[TM] or glycerine) with latex condoms (oil-based lubricants-e.g.,
petroleum jelly, shortening, mineral oil, massage oils, body lotions, or
cooking oil-that can weaken latex should never be used); and 7) holding
the condom firmly against the base of the penis during withdrawal and
withdrawing while the penis is still erect to prevent slippage.
Condoms should be stored in a cool, dry place out of direct sunlight and
should not be used after the expiration date. Condoms in damaged packages
or condoms that show obvious signs of deterioration (e.g., brittleness,
stickiness, or discoloration) should not be used regardless of their
expiration date.
Natural-membrane condoms may not offer the same level of protection
against sexually transmitted viruses as latex condoms. Unlike latex,
natural-membrane condoms have naturally occurring pores that are small
enough to prevent passage of sperm but large enough to allow passage of
viruses in laboratory studies (2).
The effectiveness of spermicides in preventing HIV transmission is
unknown. Spermicides used in the vagina may offer some protection against
cervical gonorrhea and chlamydia. No data exist to indicate that condoms
lubricated with spermicides are more effective than other lubricated
condoms in protecting against the transmission of HIV infection and other
STDs. Therefore, latex condoms with or without spermicides are
recommended.
The most effective way to prevent sexual transmission of HIV infection and
other STDs is to avoid sexual intercourse with an infected partner. If a
person chooses to have sexual intercourse with a partner whose infection
status is unknown or who is infected with HIV or other STDs, men should
use a new latex condom with each act of intercourse. When a male condom
cannot be used, couples should consider using a female condom.
Data from the 1988 National Survey of Family Growth underscore the
importance of consistent and correct use of contraceptive methods in
pregnancy prevention
(ref 8). For example, the typical failure rate during the
first year of use was 8% for oral contraceptives, 15% for male condoms,
and 26% for periodic abstinence. In comparison, persons who always abstain
will have a zero failure rate, women who always use oral contraceptives
will have a near-zero (0.1%) failure rate, and consistent male condom
users will have a 2% failure rate (ref 9). For prevention of HIV infection and STDs, as with pregnancy prevention, consistent and correct use is crucial.
The determinants of proper condom use are complex and incompletely
understood. Better understanding of both individual and societal factors
will contribute to prevention efforts that support persons in reducing
their risks for infection. Prevention messages must highlight the
importance of consistent and correct condom use (ref 10).
References
1.CDC. Condoms for prevention of sexually transmitted diseases. MMWR 1988;37:133-7.
2. Cates W, Stone KM. Family planning, sexually transmitted diseases, and contraceptive choice: a literature update. Fam Plann Perspect 1992;24:75-84.
3. Weller SC. A meta-analysis of condom effectiveness in reducing sexually transmitted HIV. Soc Sci Med 1993;1635-44.
4. 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.
5.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.
6.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.
7.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.
8. Jones EF, Forrest JD. Contraceptive failure rates based on the 1988 NSFG. Fam Plann Perspect 1992;24:12-9.
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.
10. Roper WL, Peterson HB, Curran JW. Commentary: condoms and HIV/STD prevention -- clarifying the message. Am J Public Health 1993;83:501-3.
Note 1. Single copies of this report are available from the CDC National AIDS Clearinghouse, P.O. Box 6003, Rockville, MD 20849- 6003; telephone (800) 458-5231.
Note 2. Use of trade names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.
Update: Barrier Protection against Sexual Diseases
From the CDC National AIDS Clearinghouse
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