Use of substances may also directly contribute to risk of STD infection by undermining an individual's cognitive and social skills, thus making it more difficult to take actions needed to protect themselves against STDs. For example, at low doses cocaine can decrease inhibitions and heighten sexuality, leading to increased numbers of sexual encounters and partners and to increased high-risk sexual behaviors (Marx et al., 1991). In addition, drug users may be at greater risk for STDs as a result of the practice of trading sex for drugs; in these situations, drug users have a large number of high-risk partners (Marx et al., 1991). Those who are involved in frequent and sustained use of substances are most likely to be at risk for STDs.

Data from the National Household Survey on Drug Abuse indicate that, in 1994, approximately 54 percent of the U.S. population age 12 and over and 63 percent of those age 18-25 used alcohol in the prior month (SAMHSA, 1995). In addition, approximately 6 percent of the U.S. population used an illicit drug in the prior month, and there were approximately 500,000 crack cocaine users during the year.

To illustrate the broad impact of substance use on STD transmission, the committee focused on the association of STDs with use of two substances: crack cocaine, often used by disenfranchised groups, and alcohol, which is commonly used by most Americans, especially adolescents. In the following sections, the committee describes the evidence for the association between substance use/abuse and STDs.

Impact of Crack Cocaine on STD Transmission

Numerous studies show that drug use is associated with increased risk of STDs, including HIV infection. Marx and colleagues (1991) reviewed 16 epidemiologic studies that examined drug use, sexual behavior, and STDs. Crack use paralleled the trends for syphilis, gonorrhea, chancroid, and HIV infection, both temporally and among the groups most affected. For example, a study at an STD clinic in 1990 in Trenton, New Jersey, evaluated the relationship between syphilis and behavior related to sexual activity and drug use (Finelli et al., 1993). The study showed that in addition to crack use and lack of condom use within the past three months, a high number of sex partners, drug-using partners, and partners exchanging sex for drugs increased the risk for syphilis, especially for women.

The association of syphilis and crack cocaine may lead to concentrations of the disease in specific social networks and in crack houses. For example, in 1991 and 1992, a series of syphilis outbreaks in four rural towns in Texas were linked to crack users exchanging sex for drugs (Schulte et al., 1994). Three outbreaks were concentrated in neighborhoods where crack cocaine dealers worked and where exchange of sex for drugs or money was common. All 26 cases in one outbreak were linked to a single sex worker. In a second outbreak, all 34 cases were among people frequenting a crack house, 3 of whom were sex workers. In

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