HIV incidence among New Haven needle exchange participants: updated estimates from syringe tracking and testing data.

This article provides updated estimates of the rate of new HIV infections among participants in New Haven's legal needle exchange program from syringe tracking and testing data. We previously reported that based on data collected from November 1990 through May 1992, the maximum likelihood incidence rate was zero with a 95% confidence interval of 0-10.2 new infections per 100 drug injectors per year. Expanding this data set through August 1993, the same statistical methods yield a maximum likelihood estimate of 1.63 new infections per 100 drug injectors per year with a 95% confidence interval of 0-7.2. Given these data, the null hypothesis of no new infections cannot be rejected, providing further support for the efficacy of New Haven's needle exchange program.