Seropositivity to multiple sexually transmitted infections is not common

Background: Seropositivity for several sexually transmitted infections (STI s) is often used as a surrogate measure of sexual behavior. The authors ass essed the concomitant seropositivity for STIs in women. Coal: To estimate the excess of concomitant seropositivity for four STIs am ong fertile-aged women assuming no coinfections above what would be expecte d at random. Study Design: Antibodies to herpes simplex virus type 2, human papillomavir us type 16, HIV, Chlamydia trachomatis, and Treponema pallidum were determi ned from a random sample of 1110 pregnant women in Tallinn, Estonia. Results: A total of 310 combinations of the concomitant seropositivity were observed, whereas only 193 were expected by chance. Among persons seroposi tive for two STIs, 78 extra combinations were observed, whereas for three S TIs, 35 extra combinations were observed. For four STIs, 3.8 extra combinat ions were found. Conclusions: Seropositivity to multiple STIs is not common. This fits the c oncept of different transmission probabilities and the spread of the STIs, and suggests that seropositivity alone should be used with caution as a sur rogate to sexual behavior in women.