Upsurge of chlamydial reinfection in a large Canadian city: an indication of suboptimal chlamydia screening practices?

OBJECTIVES: Given the limited knowledge on chlamydial reinfection (CR) in Canada, we examined the extent and predictors of CR in Montréal, a large Canadian city. METHODS: We retrospectively studied all Montréal residents aged > or =10 years for whom > or =1 laboratory-confirmed chlamydial infection was reported to the public health department between 1988 and 2007 (n = 44,580). Each person was passively followed for two years after baseline infection or until reinfection. Socio-demographic factors and histories of other notifiable diseases were examined as potential predictors. Cox multivariate regression was used to model the time to CR. Survival analyses were stratified by age group (<25 vs. > or =25 years). RESULTS: We estimated an overall two-year CR rate of 6.4%, an incidence density of 3.5 per 100 person-years, and a median time to reinfection of nine months. CR significantly increased over time. Among persons <25 years, reinfection was significantly more likely among females [adjusted hazard ratio (AHR): 1.58] and younger participants (10-14 years: AHR: 2.98; 15-19 years: AHR: 1.81). Residing within the South Central sector was deleterious for six months following initial infection after which it became protective. Among persons > or =25 years, a history of sexually transmitted infections increased the risk of reinfection (AHR: 1.79). CONCLUSION: CR is a significant and growing problem in Montreal. The current recommendation for a single repeat screening six months posttreatment might be usefully complemented with additional screenings. Our results also underscore the importance of screening high-risk populations, particularly young women.