Genital Chlamydia trachomatis infections among adolescents in a high-incidence area in Norway: genotypes, prevalence, early sexual behaviour and testing patterns – a cross-sectional study The Finnmark High School Study (FHSS)

Chlamydia trachomatis is the most commonly reported curable sexually transmitted infection in Western high-income countries and can cause severe female reproductive tract morbidity. Despite extensive control efforts, chlamydia rates have increased in most countries since the mid-1990s. Young persons and especially adolescent girls have the highest infection rates. In general, girls are tested far more frequently than boys. High-resolution genotyping provides detailed information on the molecular epidemiology and genetic diversity of C. trachomatis. In this thesis, we investigated; i) C. trachomatis genotype distribution and genetic diversity using MLST (multilocus sequence typing) and ompA genotyping in Finnmark, a high-incidence area in Norway, ii) associations between early sexual behaviour and prevalent chlamydia infection, and iii) demographic and sexual behaviour factors associated with chlamydia testing in a high school based screening and previous clinic based testing, among girls and boys aged 15-20 years who participated in the Finnmark High School Study conducted from September to November 2009. We detected a large genetic diversity, multiple novel sequence types and alleles by MLST, and an atypical genovar distribution with predominance of G in a previously unmapped area. C. trachomatis genetic diversity in rural Finnmark and two other urban areas was similar. Chlamydia prevalence in sexually active girls was 7.3% and in boys 3.9%. Girls started their sexual career and were more sexually active at an earlier age and thus had a different risk profile from boys which may contribute to higher prevalence. Threefold more girls than boys reported previous clinic based testing which was associated with known chlamydia risk factors. School based screening reached 93% of participants and was associated with factors unknown to increase risk thus suggesting other motives. Half of infections were detected in those only tested at school. We confirmed the efficiency of school based screening to increase testing and detect hidden infections and we thus suggest this approach to be tried as a complement to other chlamydia control strategies in selected high-morbidity areas in Norway