Estimating the transmission probability of human immunodeficiency virus ininjecting drug users in Thailand

We estimate the transmission probability for the human immunodeficiency vir us from seroconversion data of a cohort of injecting drug users (IDUs) in T hailand. The transmission probability model developed accounts for interval censoring and incorporates each IDU's reported frequency of needle sharing and injecting acts. Using maximum likelihood methods, the per needle shari ng act transmission probability estimate between infectious and susceptible IDUs is 0.008. The effects of covariates. disease dynamics, mismeasured ex posure information and the uncertainty of the disease prevalence on the tra nsmission probability estimate are considered.