_______________________________________________________________________ HIV/AIDS: An Update
RISK CATEGORIES On the basis of newly reported cases, the transmission cat- egories are [8; 10]: • Male-to-male sexual contact (MSM) • Injecting drug users (IDUs) • MSM who inject drugs • Heterosexual contact • Perinatal transmission • Other (includes hemophilia, blood transfusion, and risk factor not reported or not identified) The CDC has published guidelines for medical professionals to integrate HIV prevention into the regular medical care of those living with HIV. The three major components of the recommendation are: screening for HIV transmission risk behaviors and sexually transmitted infections (STIs); provid- ing brief, behavioral risk-reduction interventions in the office setting and referring selected patients for additional preven- tion interventions and other related services; and facilitating notification and counseling for sex and needle-sharing partners of infected persons [17].
Although abstinence from sexual contact is the sole way to absolutely prevent transmission, sexual activity in a mutually monogamous relationship in which neither partner is HIV- infected and no other risk factors are present is considered safe. A study of serodifferent heterosexual and MSM couples in which the HIV-positive partner was on ART found no documented cases of within-couple transmission of HIV, despite engaging in condomless sex, after an average of 1.3 years [68]. However, men who identify publicly as heterosexual and generally have committed relationships with women, but who also engage in sexual activity with other men, may be a transmission bridge to heterosexual women [10; 18]. To better understand the actual extent of this behavior and its impact on HIV transmission, more research is necessary. Numerous studies have demonstrated that oral sex can result in the transmission of HIV and other STIs. While the risk of HIV transmission through oral sex is much smaller than the risk from anal or vaginal sex, there are several co-factors that can increase this risk, including oral ulcers, bleeding gums, genital sores, and the presence of other STIs. Prevention includes the use of latex condoms, a natural rubber latex sheet, plastic food wrap, a cut open condom, or a dental dam, all of which serve as a physical barrier to transmission [10; 18]. Blood Donor Products It has been estimated that a milliliter of HIV-infected human blood contains up to 10,000 copies of the virus. In compari- son, a milliliter of blood infected with hepatitis B virus has 100 million to 1 billion infective organisms [19]. Even so, HIV is transmitted via blood, primarily through sharing of contaminated needles among IDUs and, rarely, through blood transfusion. Transmission of HIV-1 has occurred after transfu- sion of the following components: whole blood, packed red blood cells (including washed and buffy coat poor), fresh frozen plasma, cryoprecipitate, platelets, and plasma-derived products, depending on the production process. With the implementa- tion of a donor screening program of the nation’s blood sup- ply in 1985 and advances in the treatment of donated blood products, blood transfusion is now even safer; the current risk of transmission of HIV through this route is conservatively estimated to be less than 1 per 1 million [20]. It is possible that before blood screening implementation, more than 12,000 people were infected [21]. A large percentage of persons with hemophilia acquired HIV in this manner. Donor screening, HIV testing, and heat treatment of the clotting factor have greatly reduced the risks. Needle Sharing Transmission of HIV among IDUs occurs primarily through contamination of injection paraphernalia with infected blood. The risk of sustaining HIV infection from a needle stick with infected blood is approximately 1 in 300 [30]. Behavior such as needle sharing, “booting” the injection with blood, and per- forming frequent injections increases the risk. Crack cocaine use (by injection or smoking) is associated with a higher preva-
MODES OF TRANSMISSION Sexual Transmission of HIV
HIV has been isolated from blood, seminal fluid, spermatozoa, pre-ejaculate, vaginal secretions, urine, cerebrospinal fluid, saliva, tears, and breast milk of infected individuals. No cases of HIV infection have been traced to saliva or tears (though traces of the virus are present in these fluids). The virus is found in greater concentration in semen than in vaginal fluids, leading to a hypothesis that male-to-female transmission could occur more easily than female-to-male. Sexual behavior that involves exposure to blood is likely to increase transmission risks. Transmission could also occur through contact with infected bowel epithelial cells in anal intercourse, in addition to access to the bloodstream through breaks in the rectal mucosa [9; 10]. Posing the highest risk of infection is unprotected anal receptive intercourse, followed by unprotected vaginal intercourse and unprotected insertive anal intercourse (particularly for uncir- cumcised men) [9]. Risk is reduced through the use of latex condoms. For the wearer, latex condoms provide a mechanical barrier limiting penile exposure to infectious cervical, vaginal, vulvar, or rectal secretions or lesions. Likewise, the partner is protected from infectious pre-ejaculate, semen, and penile lesions. Oil-based lubricants may make latex condoms inef- fective and should not be used; water-soluble lubricants are considered safe. Natural membrane condoms (made from lamb cecum) contain small pores and do not block HIV passage. It is estimated that consistent use of latex condoms reduces the risk of HIV transmission by approximately 80% [16].
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MDCT2026
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