Number of Sexual Encounters Involving Intercourse and the Transmission of Sexually Transmitted Infections

In Brief Objective: To investigate the impact of the number of sexual encounters involving intercourse in combination with the number of sexual partners on the transmission dynamics of sexually transmitted infections (STIs). Study A statistical model is used for predicting the basic reproductive rate, R0, which takes both the number of sexual partners and the number of sexual encounters involving intercourse per partner into consideration. The model is then applied to Swedish survey data that includes data on the number of partners over the course of 1 year, as well as the number of encounters per partner during this time. Results The number of sexual encounters involving intercourse in combination with the number of sexual partners affects the number of secondary infections in a nonlinear way. The basic reproductive rate, R0, is lower when the heterogeneity in number of encounters is modeled than when homogeneity is assumed. Conclusion: The results indicate that it is possible that individuals who have a large number of partners may not, as is often assumed, be the only ones to play a central role as spreaders of STIs. Individuals who have a large number of sexual encounters involving intercourse per partner and have several (but not necessarily a very large number of) partners may also play a significant role in the transmission of STIs. An analysis of survey data on the number of sexual partners and the number of sexual encounters involving intercourse found that the basic reproductive rate (R0) is likely to be lower when heterogeneity rather than homogeneity in number of sexual encounters is assumed.