Objective To compare the prevalence of demographic characteristics and sexual behaviours across age groups and to estimate their significance in predicting sexual risk factors by age cohort.

Methods This cohort study examined sexually transmitted infection (STI) prevalence among heterosexual men in Brazil, Mexico and the USA (N=3047). Participants completed a sexual risk factor questionnaire and were tested for chlamydia, gonorrhoea, syphilis and genital herpes. We examined sexual risk in the study population through a composite measure of STI positivity by age cohort (young: 18–30 years; middle-aged: 31–44 years; older: 45–70 years). Multivariable logistic regression models were used to generate adjusted odds ratios (AORs) and 95% confidence intervals (CIs).

Results We found that STI positivity varied significantly by age group among heterosexual men by a number of covariates. In younger men, having more advanced education had a protective effect (16 years: AOR=0.37, 95% CI 0.15– 0.92), whereas higher numbers of sexual partners elevated the risk for STIs (20–49 partners: AOR=2.06, 95% CI 1.04–4.06; ≥50 partners: AOR=4.33, 95% CI 1.74–10.76). Middle-aged men who were black (AOR=1.64, 95% CI 1.10–2.42) and divorced/separated/widowed (AOR=1.91, 95% CI 1.21–3.02) had an increased risk for a positive STI test. Among older men, a younger age at first vaginal sexual encounter (AOR=3.75, 95% CI 1.45–9.74) and a history of exchanging sex for money or drugs heightened STI risk (AOR=2.30, 95% CI 1.0–5.04).

Conclusions These findings demonstrate that age-related life experiences among heterosexual men influence sexual risk and STI transmission. This topic warrants further investigation to support the development and implementation of targeted interventions that may potentially reduce adverse sexual health outcomes.