Non-monogamy and risk of infection with Chlamydia trachomatis and Trichomonas vaginalis among young adults and their cohabiting partners in Peru.

Objectives: To determine how patterns of non-monogamy influence prevalences of sexually transmitted infections (STIs) in individuals and their cohabitating sex partners. METHODS A 2002 survey in 24 Peruvian cities enrolled men and women aged 18-29 years from random household samples. The cohabiting sex partner of each enrolee was also enrolled until approximately 100 couples per city were recruited. Men provided urine and women vaginal swabs or urine for molecular testing for Chlamydia trachomatis and Trichomonas vaginalis; both genders provided blood for serological testing.

Results: Among 2099 females and 2052 males providing specimens and behavioural data, 18.2% of males and 2.5% of females reported non-monogamy during the past year. C trachomatis was detected in 121 females (5.8%) and 80 males (4.1%) and T vaginalis in 87 females (4.2%) and 26 males (1.3%). Multivariate analyses showed that C trachomatis infection in females was significantly associated with her male partner's non-monogamy (OR 2.02, CI 1.32 to 3.08) but not significantly with her own non-monogamy; T vaginalis was associated with her own non-monogamy (OR 3.11, CI 1.25 to 7.73) and with her partner's non-monogamy (OR 2.07, CI 1.26 to 3.42). For males, both C trachomatis (OR 2.17, CI 1.29 to 3.69) and T vaginalis (OR 2.49, CI 1.06 to 5.87) were significantly associated only with his own non-monogamy.

Conclusions: Among cohabiting couples, male non-monogamy was common and was associated with C trachomatis and T vaginalis infection in himself and in his female partner, whereas female non-monogamy was reported infrequently and was significantly associated only with her own T vaginalis infection. Patterns of non-monogamy may guide public health interventions.