A total of 924 eligible FSW were enrolled (474 in Tijuana and 450 in Ciudad Juarez), of whom 166 (18.0%) reported ever injecting drugs and 114 (12.3%) reported injecting illicit drugs within the last month. Relative to Cd. Juarez, higher proportions of FSWs in Tijuana reported ever injecting drugs (21.7% vs. 14.0%, p=0.002), or injecting drugs within the last month (15.8% vs. 8.7%, p=0.001).
Among FSWs who injected drugs within the last month (N=114), polydrug use was common. The majority reported injecting heroin (93.9%), cocaine/heroin combinations (i.e., “speedball”; 50.0%), cocaine alone (36.0%) or methamphetamine (21.1%). Not unexpectedly, FSW-IDUs were also more likely to report non-injection use of other drugs, including marijuana/hash, heroin and methamphetamine (). In the past month, 52.6% reported using a needle someone else had used, 73.7% had passed on their own needle to someone else, and 70.3% had shared injection paraphernalia (i.e., cottons, cookers, rinse water). One fifth reported sharing needles with a sex trade client (18.9%).
Characteristics of IDU and Non-IDU FSWs in Tijuana and Cd. Juarez
Compared with FSWs who did not inject drugs within the past month FSW-IDUs were slightly younger (30 vs. 33 years), more likely to be married/common-law, speak English, mainly work on the street rather than a bar, and have been a sex worker for a longer duration. In contrast, compared to other FSWs, FSW-IDUs were less likely to have had children, live in their own home, and reported living with fewer people ().
In terms of social influence, FSW-IDUs were more likely to report having a steady partner who was also an IDU and fellow FSWs who injected drugs, but were no more likely to report having a pimp or to have clients who used drugs compared to non-IDUs. Compared to other FSWs, FSW-IDUs had greater numbers of clients, and were paid significantly less for sex with a condom. There was no significant difference between FSWs and FSW-IDUs for average amount earned for sex without a condom, or in the median difference earned for vaginal sex with and without a condom ().
In terms of risk behaviors, the groups did not differ in terms of the proportions who had vaginal sex without a condom, although FSW-IDUs were marginally less likely to use a condom for anal sex. FSW-IDUs were less likely to use alcohol before or during sex, but were more likely to use illicit drugs in these situations. FSW-IDUs were also more likely than other FSWs to report at least one IDU sex partner in the last month and have male clients that currently use or inject drugs ().
Compared to other FSWs, FSW-IDUs were more likely to have an STI at baseline including HIV, syphilis, Chlamydia, and gonorrhea. HIV prevalence was 12.3% among FSW-IDUs, relative to 5.1% among other FSWs. Overall, 44.7% of FSW-IDU had at least one of these STIs, compared to 24.4% among other FSW (p<0.01) ().
We examined correlates associated with being an FSW-IDU in univariate logistic regression models. A generally risky pattern emerged. FSW-IDU were more likely to describe oneself as a street worker (OR=5.05, 95% CI 3.00-8.51 ), be married/common-law (OR=2.35, 95% CI 1.56-3.55), and live in Tijuana as opposed to Ciudad Juarez (OR=1.98, 95% CI 1.30-2.99). The odds of being an FSW-IDU were lower for those who lived in their own home and those who worked mainly in a bar. Sex workers whose steady partner was an IDU (OR=12.19, 95% CI 6.24-23.79) and who reported that most fellow FSWs were IDUs were more likely to be FSW-IDUs (OR=1.80, 95% CI 1.50-2.16). Sex workers who often or always used drugs before sex and those who had more clients with whom they had unprotected vaginal sex acts were much more likely to be FSW-IDUs. Finally, FSW-IDUs were more likely to be HIV positive (OR=2.63, 95% CI 1.38-4.99) and to test positive for at least one STI ().
Factors Associated with Recent Injection Drug Use among FSWs in Tijuana and Cd. Juarez
In the final multivariate model, a number of factors were independently associated with recent injection drug use within this FSW population. After controlling for site and all other factors, FSW-IDUs were more likely to describe themselves as a street worker (OR=3.85), speak English (OR=2.79), be married/common law (OR=2.01), have worked in the sex trade for more than four years (OR=2.12), to have lived for a longer duration in the study location and to report that some of their fellow sex workers were IDUs (OR=2.42) (). In contrast to other FSWs, those who injected drugs were younger, less likely to live in their own home, and less likely to have had children. They were also less likely to live and work in the same location, and were more likely to have been paid less than $30 US on average for sex with a condom.
Factors Independently Associated with Recent Injection Drug Use among FSWs in Tijuana and Cd. Juarez
Variables that did not retain significance at the 5% level in the multivariate model included being born in the state where they now live, education level, total number of people they live with, mainly working in a bar, whether their steady partner was an IDU, having at least one IDU sex partner in the last month, having male clients who currently use drugs or have injected drugs, median number of clients in the last six months, number of unprotected vaginal sex acts with clients in the last six months, often or always having protected anal sex, and often or always using alcohol before vaginal sex.
Repeating the analysis to compare FSWs who ever injected drugs to those who had never injected yielded similar findings (results not shown).