Surprisingly Low Sexually Transmitted Disease Rates Found Among Drug Users
The prevalence rates of chlamydia (3%), gonorrhea (0.4%) and HIV (6%) infection are moderate among drug users at a disease prevention and needle-exchange program in Canada, although clients report high rates of risky behaviors.1 The prevalence of HIV infection is higher among those who currently use injection drugs (10%) than among former injection-drug users (6%) or among those who have never used injection drugs (0%).
Researchers recruited 738 drug users attending a sexually transmitted disease (STD) and needle-exchange program in downtown Quebec City.* Between February and April 1997, participants provided information about their demographic characteristics, medical history, sexual behavior and drug use in the six months prior to the interview. They also provided a urine sample that was tested for chlamydia, gonorrhea and HIV. Participants were advised that they could return to the clinic to receive their chlamydia and gonorrhea test results, as well as free treatment if they were infected. HIV test results, however, were not made available, as urinalysis is not yet accepted as a valid diagnostic test for HIV in Canada. Information about other sources of HIV testing was provided, and participants received a $10 payment for their time.
The researchers performed statistical analyses separately for women and men, grouping participants according to their injection-drug use status. They calculated the prevalence of disease and then conducted multiple regression analyses (which took into account participants' injection-drug use and gender, as well as factors that were significant at the univariate level) to assess the independent effects of various risk factors. Chlamydia and gonorrhea were analyzed separately from HIV infection.
Two-thirds of participants were male, and one-third were female; this distribution reflects the usual proportion of men and women who attend the clinic. On average, men were older than women (29.7 vs. 25.4 years) and were more likely to have spent time in prison (58% vs. 34%). Fifty-eight percent of participants had attended the clinic for more than two months, and 72% of this group were currently injecting drugs. Among those attending the clinic for the first time during the study, 12% were current injection-drug users.
Fifty-one percent of men and 39% of women were currently using injection drugs. The mean length of time that men had been using injection drugs was 8.3 years; the mean for women was 7.1 years. Roughly 20% of injection-drug users had knowingly ever shared a needle with an HIV-infected person, and a similar proportion had injected in a shooting gallery in the past six months. Approximately one-third of injection-drug users said that they had borrowed used needles during the six months prior to the study.
Among participants who were not currently injecting drugs, 28% had ever done so, but not in the six months prior to the study; 32% of male and 22% of female nonusers fell into this category. Virtually all clients reported having used drugs or alcohol during the previous six months. Injection-drug users were more likely than other participants to have used cocaine (96% vs. 37%), PCP (54% vs. 37%) and heroin (24% vs. 2%). Male clients who were injection-drug users were more likely than nonusers to report a history of hepatitis (33% vs. 7%) or HIV infection (7% vs. 2%), and female injection-drug users were more likely than other women to have had STDs in the past (50% vs. 32%) and HIV infection (14% vs. 0%).
Eight participants were sexually inexperienced and were excluded from the analyses. The mean age of sexually experienced participants at first intercourse was 14 years. Eighty percent of men and 94% of women had had a heterosexual partner during the six months prior to the survey; 1% and 12%, respectively, had had at least 20 such partners. Overall, women were more likely to report using condoms consistently with commercial partners than with regular partners (66% vs. 18%, respectively). There were not enough men with commercial partners to make comparisons concerning condom use with these partners.
Many participants had engaged in sex with risky partners. Thirty-five percent of men and 42% of women had had unprotected intercourse with a partner who used injection drugs; 15% and 11%, respectively, with a homosexual or bisexual man; 27% and 11% with a prostitute; and 5% of each with an HIV-positive partner. Approximately two-thirds of men and women had had unprotected intercourse with a partner who had multiple sex partners. Injection-drug users reported higher rates of these behaviors than nonusers.
STD Prevalence and Risk
Overall, 4% of women and 3% of men had chlamydia; 1% of women and no men had gonorrhea. At the univariate level, the prevalence of these STDs was essentially the same among all male injection-drug users, regardless of whether they reported risky behavior. However, among men who were not injecting drugs, those who had first had intercourse before age 13 were significantly more likely to be infected than were those who had begun having sex at a later age (11% vs. 2%). The prevalence of STDs was also higher among those who had had regular sexual partners in the past six months than among those who had not (7% vs. 1%), and it rose from 3% among men who had had no more than one female partner in the past six months to 13% among those who had had more than five partners during the same period.
Similarly, the proportion of women with chlamydia or gonorrhea did not vary among injection-drug users, but a number of factors were related to prevalence of these infections among nonusers. Among women who did not inject drugs, those who had been attending the program for more than two months had a higher prevalence of disease than those who had been coming for less time (13% vs. 3%), prevalence was higher among cocaine users than among nonusers (12% vs. 1%), and clients who had first had sex before age 13 were more likely to be infected than those who had waited (19% vs. 3%).
In the multiple regression analysis, the researchers found that women were at increased risk of having chlamydia or gonorrhea if they were aged 20-24 (odds ratio, 6.5) or if they had had unprotected intercourse with a commercial partner (7.5). Men who were not injection drug users had elevated odds of disease if they had had intercourse with a regular partner during the six months prior to the interview (9.7). Among all men and women who did not use injection drugs, being younger than 13 at first intercourse and having used cocaine during the previous six months were also associated with an increased likelihood of STDs (6.1 and 5.3, respectively).
Six percent of participants (5% of men and 6% of women) tested positive for HIV; 68% of this group were already aware of their infection. All clients who had HIV had injected drugs, although the prevalence of infection was significantly lower among former users (6%) than among those who were currently injecting drugs (10%).
Among injection-drug users, the prevalence of HIV was higher for women than men (15% vs. 8%), and increased from 2% among clients younger than age 20 to 17% among those in their 30s. Infection with HIV was more prevalent among those who had spent time in prison than among those who had not (14% vs. 3%), and among those who had had hepatitis than among those who had not (21% vs. 4%). Injection-drug users who had engaged in any risky behavior had at least twice the risk of infection as those who had not. In some instances, the differential was striking. For example, 31% of those who had shared needles with an HIV-infected person tested positive for the virus, compared with 5% of those who had not; the prevalence of infection was 45% among those who had had unprotected sex with an HIV-infected partner, but 7% among those who had never done so.
According to results of the multivariate analysis, women, participants who had had hepatitis and those who had had fewer than two heterosexual partners in the past six months had an elevated likelihood of HIV infection (odds ratios, 2.6-3.4). The odds of HIV infection were even higher among those who reported having shared needles with an HIV-infected person (6.5).
The primary limitations of the study, as reported by the authors, are possible selection bias, as many drug users may have chosen not to attend the clinic while the research was under way, and the study's reliance on the retrospective, self-reports of participants' behaviors. Nonetheless, the researchers contend that the study provides support for the idea that "needle-exchange program sites may offer a good opportunity to provide complete prevention and medical services to [drug users]."--M. Moore
*Thirty-six of the female participants were recruited through the Quebec Detention Center.
1. Poulin C et al., Prevalence of Chlamydia trachomatis, Neisseria gonorrheae, and HIV infection among drug users attending an STD/HIV prevention and needle-exchange program in Quebec City, Canada, Sexually Transmitted Diseases, 1999, 26(7):410-420.