INCIDENCE AMONG NEEDLE EXCHANGE PARTICIPANTS - ESTIMATES FROM SYRINGETRACKING AND TESTING DATA

This paper develops a statistical procedure for estimating the HIV inf ection rate among needle exchange clients without using any self-repor ted information. Instead, data are accumulated by following the distri bution and return of sequentially labeled syringes and by testing a sa mple of returns for the presence of HIV-1 proviral DNA using polymeras e chain reaction. For each drug injector in the sample, a maximum like lihood change point model is constructed to determine if a statistical ly significant upward shift in the fraction of needles testing HIV pos itive is evident, as would occur if the drug injector in question beca me infected. A second maximum likelihood model is formulated to estima te the HIV incidence rate among needle exchange participants by aggreg ating the individual change point results. When these methods are appl ied to the syringe tracking and testing data collected to evaluate the legal needle exchange program in New Haven, Connecticut, the maximum likelihood incidence estimate equals zero, with a 95% confidence inter val of 0-10.2 new infections per 100 drug injectors per year. Given th ese data, we cannot reject the null hypothesis that no new infections have occurred among needle exchange participants between November 1990 and May 1992.