Patterns of sex worker-client contacts and their implications for the persistence of sexually transmitted infections.

Sex workers (SWs) and their clients are often identified as being central in transmission of sexually transmitted infections (STIs). Little is known about how patterns of contact between SWs and their clients influence the persistence of STIs. We developed an individual-based simulation model to explore how variation in number of client contacts per SW, whether clients repeatedly visited the same SW, and the relative sizes of the SW and client populations influence the endemic prevalence of gonorrhea and herpes simplex virus type 2 infection. Persistence of either infection was more likely if clients visited many different SWs, regardless of variation in the SW-client contact rate, and also resulted in a higher endemic prevalence in both populations and a greater likelihood of persistence of infection at lower levels in the general population. The size of the SW population (relative to the total population) was found to be most important in determining the overall prevalence of infection.