Genital C. trachomatis infections clear more slowly in men than women, but are less likely to become established

Background: Rigorous estimates for clearance rates of untreated chlamydia infections are important for understanding chlamydia epidemiology and designing control interventions, but were previously only available for women.

Methods: We used data from published studies of chlamydia-infected men who were re-tested at a later date without having received treatment. Our analysis allowed for new infections take one of one, two, or three courses, each clearing at a different rate. We determined which of these three models had the most empirical support.

Results: The best-fitting model had two courses of infection in men, as was previously found for women: ‘slow-’ and ‘fast-clearing’. Only 68% (57%-78%) (posterior median; 95%CrI) of incident infections in men were ‘slow-clearing’, versus 77% (69%-84%) in women. The slow clearance rate in men (based on six months’ follow-up) was 0.35 (0.05-1.15) year-1, corresponding to mean infection duration 2.84 (0.87-18.79) years. This compares to 1.35 (1.13-1.63) years in women.

Conclusions: Our estimated clearance rate is slower than previously assumed. Fewer infections become established in men than women but once established, they clear more slowly. This study provides an improved description of chlamydia’s natural history to inform public health decision-making. We describe how further data collection could reduce uncertainty in estimates.