TABLE 1.

Incidence of HIV infection among IDUs in Xinjiang Autonomous Regions, China, in 2002

Method	No. of participants	No. HIV+a	No. BED-CEIA+b	% HIV-1 incidence (95% CI)c
Cross-sectional surveyd	1,170	225	34	8.2 (5.9-11.5)
Cohort study (HPTN033 Xinjiang cohort)e	475	42		8.8 (6.4-12.0)

^aNumber of participants whose serum tested positive in an EIA, with confirmation with Western blotting.

^bNumber of participants whose results were categorized as recent infections by BED-CEIA.

^c95% CI, 95% confidence interval. For the cross-sectional survey, the estimated incidence is a rate, and we applied the natural log scale transformation to compute variances and calculate the 95% CI for the incidence estimate as exp(log[I] ± 1.96/SQRT [Ninc]) (1). For the HPTN033 Xinjiang cohort study, HIV-1 incidence is the cumulative, annualized observed incidence, expressed as the number of new infections per 100 person-years.

^dA cross-sectional study randomly recruited 1,170 participants concurrently with the HPTN033 Xinjiang Cohort amid the same IDU population; 225 of the 1,170 participants were proved to be HIV positive by the EIA screening test, confirmed by Western blotting.

^eHIV Prevention Trials Network 033 (HPTN033) is a prospective cohort study. Participating IDUs were enrolled with 6 months of accrual and two semiannual follow-up visits. Participants were screened for seroconversion every 6 months.