Epidemiology

HIV infection has reached pandemic proportions, with life-spans in some underdeveloped nations significantly shortened as a result of widespread infection. As of the end of 1997, an estimated 30.6 million people worldwide have been living with HIV (2). Twenty nine and one half million of those individuals are adults and 1.1 million are children younger than the age of 15 yr. Approximately 41% of HIV-infected adults are women, and trends indicate that this proportion is growing. Worldwide, heterosexual transmission accounts for about 75% of all infections (2). Among children and infants, perinatal transmission accounts for >90% of infections (2). HIV infection rates in underdeveloped countries far exceed rates in developed nations. It is estimated that in 1997 more than 90% of all new HIV infections occurred in developing countries (2). The high rates of infection and mortality in these countries have significantly affected average life-spans. Lack of education, preventative efforts, and access to affordable antiretroviral medications all contribute significantly to the global spread of HIV.

In the United States, AIDS was the leading cause of death in young men in 1996. Encouragingly, new AIDS cases reported to the Centers for Disease Control (CDC) declined 12% from 1996 to 1997 (3). Deaths from AIDS also fell by 47% from 1996 to 1997. According to the CDC, AIDS is no longer the number one cause of death in American men aged 25-44 (2,3). This decline in disease progression is believed to primarily result from the use of new, potent antiretroviral medications. An estimated 665,357 people were living with AIDS in the United States as of the end of June 30, 1998 (3). Similar to worldwide trends, the number of AIDS cases among women in the United States has steadily increased to 22% since 1985. Caucasians account for the largest percentage of infected Americans at 45%. Men having sex with men (MSM) account for the greatest percentage of cases (45%), followed by injection drug users (22%). Transmission by heterosexual contact, while not accounting for the majority of cases in the US, has steadily increased since 1991 to 17.5%. Unfortunately, while AIDS-related death rates in the United States continue to decline, infection rates remain unchanged (2).

HIV is not transmitted by casual contact (4). Transmission of the virus requires the exchange of specific bodily fluids that contain viral particles (4). Blood and semen have the greatest viral burden and thus carry the highest risk of disease transmission.

The virus itself appears to be highly labile, unable to survive in the environment for more then a few hours. Transmission most commonly occurs when bodily fluids are exchanged during sexual contact (5). Anal intercourse, because of its traumatic nature, carries the greatest risk of transmission, followed by vaginal intercourse and receptive oral sex (5). When used appropriately, barrier methods such as latex condoms and dental dams have been shown to reduce the risk of transmission from sexual contact. However, it must be emphasized that condoms and other barrier methods do not entirely eliminate risk.

Intrauterine transmission is the most common cause of infant and pediatric HIV infection (7). Treatment of mother and baby with zidovudine may reduce the potential for perinatal transmission by up to 67.5%. To reduce the risk of intrauterine transmission, zidovudine should be administered at doses of 100 mg p.o. five times per day at 14-34 wk of gestation, followed by zidovudine 2 mg/kg i.v. load and 1 mg/kg/h during delivery (6). The neonate should then be given zidovudine 2 mg/kg p.o. q6h for the first 6 wk of life. Because monotherapy of infected individuals including pregnant women is no longer considered acceptable, many clinicians now advocate treating women with triple highly active antiretroviral therapy. Studies are underway to determine the optimal and most cost-effective drug regimens for prevention of perinatal transmission.

The use of unclean needles by injection drug users is also a common mode of viral transmission. If sterile needles are not available, disinfection of used needles with full stength bleach should be encouraged. The implementation of standard precautions has lowered the incidence of needlesticks within occupational settings. Standard precautions dictate that blood and other high-risk bodily fluids from all patients should be considered potentially infectious. Thus, appropriate personal protection equipment (e.g., masks, gowns, gloves) should be employed when caring for all patients in situations where contact with body fluids is anticipated. The risk of contracting HIV from a needlestick is estimated to be 0.32% (7). The risk of seroconversion is increased when the source patient has end-stage disease accompanied by a high HIV titer. The use of post-exposure prophylaxis (PEP) appears to reduce the risk of transmission by as much as 79% (8). PEP should be offered in all cases of a needlestick from an HIV+ patient (7). Current guidelines call for a three-drug regimen to be initiated as soon after the exposure as possible. The three-drug regimen most commonly advocated consists of a 30-d course of: zidovudine 300 mg p.o. b.i.d., lamivudine 150 mg p.o. b.i.d., and indinavir 800 mg p.o. q8h (9). Recipients of accidental needlesticks should receive HIV ELISA testing at baseline, then 6 wk, 12 wk, and 6 mo post-exposure (9). The increasing frequency of resistant HIV strains has led some experts to advocate tailoring recommendations for PEP based on the sensitivities of the source patient's virus, if known.

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