Amphetamine, and its common derivative methamphetamine (also known as speed or crystal meth), is a powerfully addictive stimulant drug that can be taken by mouth, smoked, injected, or taken rectally (‘booty bumping’). Methamphetamine abuse has significantly increased across the United States in the past decade, as evidenced by the increasing numbers of methamphetamine laboratory seizures  and methamphetamine-related admissions to emergency rooms in metropolitan areas . This trend is of particular concern, because the recreational use of amphetamine has been shown to be associated with unprotected sexual intercourse and HIV infection in men who have sex with men (MSM) [3–5]. Whereas unsafe amphetamine injection practices may directly lead to parenteral HIV transmission, more common non-injection use may facilitate sexual HIV transmission, either by enhancing sexual desire, impairing safer sex decision-making, and predisposing to unprotected sex, or by making the anal mucosa more susceptible to HIV infection, or both. In a cross-sectional survey of 295 gay and bisexual men from the San Francisco Bay area who attended a ‘circuit’ party in the previous year, 36% reported using crystal methamphetamine during a ‘circuit’ weekend , and these methamphetamine users were approximately 2.5 times more likely than non-users to report unprotected anal sex with a partner of opposite or unknown HIV serostatus during a ‘circuit’ weekend . The objectives of our analysis were: (1) to assess the frequency of recent (in the past year) amphetamine use among MSM who sought HIV testing at the AIDS Health Project (AHP), a large network of anonymous HIV testing sites in San Francisco in 2001 and 2002; (2) to examine the sociodemographic and behavioral correlates of amphetamine use; and (3) to evaluate the association between amphetamine use and HIV seroconversion in MSM who did not inject any drugs.
The serological testing algorithm for recent HIV seroconversion (STARHS) was used to identify men who recently HIV seroconverted (a mean seroconversion period of 170 days) and estimate the annual HIV incidence . We analysed demographic and risk factor data collected by trained counselors on standardized pre-test HIV counseling forms. The data were collected for the use of all amphetamines combined. However, anecdotally, counselors estimated that more than 90% to nearly all MSM at AHP who use amphetamine are using methamphetamine. Analyses were restricted to MSM who had male sex partners in the past year and who did not inject drugs. Because we found no appreciable differences in the frequency of reported amphetamine use or its association with HIV incidence comparing years 2001 and 2002, we analysed 2-year data in aggregate.
The 2991 MSM included in the analysis had a median age of 34 years; 71% were white, 10% were Hispanic or Latino, 11% were Asian or Pacific Islanders, and the remaining 8% were of other race or ethnicity. Forty percent reported having had 10 or more sex partners in the past year, and 52% reported engaging in unprotected anal sex in the past year. Overall, 290 MSM (9.7%) reported using amphetamine in the past year, and 236 (7.9%) reported having sex while using amphetamine. Compared with non-users, amphetamine users were more likely to report either unprotected anal sex in the past year [odds ratio (OR) 2.3, 95% confidence interval (CI) 1.8, 3.0] or 10 or more sex partners in the past year (OR 2.5, 95% CI 2.0, 3.3). In addition, amphetamine users were more likely to be under 35 years of age (P < 0.05), but were no more likely to belong to any racial or ethnic group.
Of 2991 MSM who were HIV tested, 108 (3.6%) were HIV seropositive, and of these 34 (31%) had evidence of recent HIV infection by STARHS. Of 34 HIV seroconverters, eight (24%) had used amphetamine in the past year. The overall calculated HIV incidence was 2.5% per year (95% CI 1.5–3.5). HIV incidence among amphetamine users was 6.3% per year (95% CI 1.9–10.6), compared with 2.1% per year (95% CI 1.3–2.9) among non-users (RR 3.0; 95% CI 1.4–6.5); the incidence was 7.7% per year (95% CI 2.4–13.0) among those who had sex while using amphetamine. After adjusting for age, race or ethnicity, and the use of other non-injectable drugs in the past year (barbituates, cocaine, ecstasy, heroin, LSD, PCP, poppers and tranquilizers), amphetamine use was still associated, but less strongly, with HIV seroconversion [odds ratio (OR) 2.4, 95% CI 0.9–6.3]. When we further controlled for the use of marijuana and alcohol in the past year, reported by 33 and 74% of MSM, respectively, amphetamine use remained associated with HIV seroconversion (OR 2.5, 95% CI 0.9–6.9).
We recognize several limitations to our study. First, MSM who test for HIV at anonymous public HIV testing sites may not be representative of all MSM, so findings might not be generalizable to the larger MSM community in San Francisco and elsewhere. Second, some HIV-negative men may have tested anonymously more than once, which would probably underestimate the HIV incidence rate. Third, individuals may underreport recent amphetamine use and other risk behaviors during face-to-face HIV pre-test counseling sessions. The underreporting of amphetamine use would probably weaken the observed association between amphetamine use and HIV seroconversion. Fourth, we may have failed to control for some factors that could either confound or modify the relationship between amphetamine use and HIV seroconversion, such as, for example, the use of Viagra (sildenafil citrate), which is often taken concurrently with amphetamines to enhance sexual performance [8,9]. Finally, STARHS may misclassify some individuals with long-standing HIV infection who have low levels of HIV antibodies (often associated with AIDS or the use of antiretroviral therapy) as recently HIV infected , thus potentially leading to overestimates of HIV incidence. However, the degree of this bias in our study is probably small, because HIV seroprevalence among MSM HIV testers at AHP sites was 3.6%, suggesting that few had long-standing HIV infection because few individuals would use anonymous services for confirmatory testing.
Our finding that recent amphetamine use is associated with unprotected anal sex and incident HIV infection among MSM is particularly worrisome because of anecdotal increases in the use of amphetamines by MSM in San Francisco in the past few years. The finding is also corroborated by the reported high prevalence of sexually transmitted diseases among methamphetamine-using MSM in the municipal sexually transmitted disease clinic in San Francisco , and a recent epidemic increase in syphilis among MSM in San Francisco . We recommend that HIV counselors and medical providers collect detailed behavioral risk histories, and counsel their clients and patients on the dangers of amphetamine addiction and on the link between amphetamine use, high-risk sex practices, and HIV infection. We also recommend expanding research and treatment programmes for amphetamine dependence, as well as launching specific educational campaigns to prevent HIV infections related to amphetamine use among MSM in San Francisco.
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