Background Chlamydia is an important public health problem associated with neonatal sequelae, pelvic inflammatory disease, infertility, and ectopic pregnancy.

Methods Using a population model with 2 genders and ages 15–44 years in 5-year groups, but only heterosexual contacts, we evaluated the impact of actual and hypothetical interventions on chlamydia in the U.S. Parameters were obtained from the literature or estimated from the National Health and Social Life Survey and Seattle Sex Survey. The model was calibrated by adjusting gender-specific probabilities of infection on contact. We calculated the basic reproduction number (R₀), defined as the average number of secondary infections per infectious person in a wholly-susceptible population without interventions. We also calculated the age- and gender-specific equilibrium prevalence and contributions to R₀. And we assessed the impact of interventions by comparing reproduction numbers with and without them. To assess the feasibility of opportunistic screening, we analysed Market Scan, a commercial health insurance database, to determine the proportion of people seeking medical care.

Results Treating symptomatic men and women who seek care and screening 38% of women aged 15–24 years during annual examinations more than halve the reproduction number. The equilibrium age- and gender-specific prevalence of infection match those observed in the National Health and Nutrition Examination Survey. Men cause more secondary infections than women (contributing twice as much to R⁰ in some age groups), and people aged 25–29 years cause as many as those aged 20–24. Analysis of the Market Scan database indicates that insured men seek care often enough for screening to have substantial impact. Screening women reduces the reproduction number by 3%; screening a similar proportion of young men would reduce it another 4%.

Conclusions Our modelling suggests that screening men as well as women and extending the upper age to 29 years may affect chlamydia transmission or sequelae.