Ti et al. BMC Public Health 2012, 12:189 http://www.biomedcentral.com/1471-2458/12/189 < secondary school), heroin injection in the past six months (> once per week vs. ≤ once per week), midazo- lam injection in the past six months (> once per week vs. ≤ once per week), methamphetamine injection in the past six months (> once per week vs. ≤ once per week), lent or borrowed syringes to/from others in the past six months (yes vs. no), enrolled in voluntary drug treat- ment in the past six months (yes vs. no), had unpro- tected sex in the past six months (yes vs. no), incarceration in the past six months (yes vs. no), report- ing barriers to accessing health services (any barriers vs. no barriers), and having ever been to MSHRC (yes vs. no). Our barriers to testing variable included the follow- ing: limited hours of operation, long wait times, didn’t know where to go, jail, detention, prison, no identifica- tion, identification registered somewhere else, no money, was treated poorly by healthcare professionals, fear of sharing information of drug using status with the police and/or narcotics control board, difficulty keeping appointments, transportation, and others. Additionally, because Bangkok was a site of the tenofovir trial (a pre- exposure prophylaxis trial) that included IDU, being enrolled in the tenofovir trial (yes vs. no) was also con- sidered in the first bivariate analyses focused on HIV testing behaviour in the past six months. All p-values were two-sided. Results In total, 244 individuals who were HIV-negative or of unknown HIV serostatus were included in the study, including 77 (31.6%) females. The median age of the participants at the time of interview was 37 years (range: 20 - 72 years). In total, 186 (76.2%) participants reported that they had been tested for HIV in the past six months. As indicated in Table 1, results show that being enrolled in voluntary drug treatment in the past six months (odds ratio [OR] = 2.34; 95% confidence interval [CI]: 1.18 - 4.63) and being in the tenofovir trial (OR = 44.81; 95% CI: 13.44 - 149.45) were positively associated with having been tested for HIV. As well, having been to MSHRC (OR = 1.78; 95%CI: 0.96 - 3.29) was margin- ally associated with having been tested for HIV. Although the odds ratio for the incarceration variable could not be calculated because one cell contained a zero, there was a trend towards a positive association between having been incarcerated in the past six months and having been tested for HIV. Of the 58 participants who were not tested for HIV, 41 responded to the ques- tion: “Why haven’t you taken an HIV test?” Of these, 27 (65.9%) stated that they believed they were HIV-nega- tive. However, 33 (56.9%) participants who did not get an HIV test engaged in at least one of the following risky behaviours in the past six months: syringe Page 3 of 9 borrowing, syringe lending, or unprotected vaginal or anal intercourse. In total, 181 (74.2%) participants responded that they were willing to get tested at the MSHRC. As shown in Table 2, factors positively associated with a willingness to be tested for HIV at the MSHRC included being enrolled in voluntary drug treatment in the past six months (OR = 1.94; 95%CI: 1.02 - 3.68), reporting a bar- rier to accessing health services (OR = 1.99; 95%CI: 1.05 - 3.77), and having been to the MSHRC (OR = 3.17; 95%CI: 1.68 - 6.01). There was also a marginally signifi- cant association between willingness to get tested at the MSHRC and having lent or borrowed syringes to/from others in the past six months (OR = 2.36; 95%CI: 0.94 - 5.90). Additionally, female sex was negatively associated with willingness to be tested for HIV at the MSHRC (OR = 0.46; 95%CI: 0.26 - 0.84). Table 3 presents the results of multivariate analyses of factors associated with willingness to get HIV testing at the MSHRC. As indicated here, having been to the MSHRC (adjusted odds ratio [AOR] = 2.42; 95%CI: 1.21 - 4.85) remained positively associated with willingness to get HIV testing at the peer-run drop-in centre. An ana- lysis of interactions was then conducted between gender and enrolment in voluntary drug treatment in the past six months. A positive association between willingness to be tested at the MSHRC and being enrolled in volun- tary drug treatment was found for females (AOR = 9.38; 95%CI: 1.14 - 76.98), while a marginal positive associa- tion between willingness to get tested for HIV at the MSHRC and non-enrolment in voluntary drug treat- ment was found for males (AOR = 2.07; 95%CI: 0.98 - 4.39). Discussion In the present study, we found that HIV testing was common among Thai IDU, with 76.2% reporting that they had been tested in the past six months. Having been enrolled in voluntary drug treatment and being enrolled in the tenofovir trial was positively associated with having been tested for HIV, while having been to the MSHRC was marginally associated. Among those who had not been tested for HIV in the past six months, approximately 56% had recently engaged in some form of HIV risk behaviour. We also found that almost three-quarters of the sample (74.2%) expressed willingness to get tested for HIV at the drug-user-run MSHRC. In a multivariate analysis, having been to MSHRC was independently and positively associated with willingness to get tested at MSHRC. Enrolment in voluntary drug treatment was also associated with will- ingness to get tested at the MSHRC, although this rela- tionship interacted with gender, with women in