Incident Chlamydia trachomatis Infection in a High School Population

SIMPLE SUMMARY: After a pathogen that causes disease has been introduced in a human population, an understanding of that disease in the population depends on knowing how many people in the population have the disease (prevalence), how fast the disease spreads from one person to another within the population (incidence), and how long the disease remains in an individual once acquired (duration). Infections caused by Chlamydia trachomatis are the most common sexually transmitted bacterial infections in the world. Individuals younger than 25 are the most affected due to the patterns of their sexual activity. In most individuals, these infections do not produce symptoms. Thus, affected individuals usually are not prompted to seek care, and most cases can only be detected through screening. Screenings for chlamydia in United States schools have given an indication of how many adolescents in the population might have chlamydia. In this study, we assessed how quickly chlamydia is acquired within the adolescent population. We determined that 14–19-year-old adolescents are acquiring chlamydia at a pace of 6.6 cases per 100 person-years for boys and 11.9 cases per 100 person-years for girls. Male and female students are acquiring chlamydia within 10 and within 7 months, respectively. ABSTRACT: Prospective cohort studies of sexually transmitted infections (STIs) are logistically impractical owing to time and expenses. In schools, students are readily available for school-related follow-ups and monitoring. Capitalizing on the logistics that society already commits to ensure regular attendance of adolescents in school, a school-based STI screening in New Orleans made it possible to naturally observe the occurrence of chlamydia and to determine its incidence among 14–19-year-old adolescents. Among participants screened repeatedly, we calculated incidence rates, cumulative incidence, and incidence times. Male (n = 3820) and female (n = 3501) students were observed for 6251 and 5143 person-years, respectively, during which 415 boys and 610 girls acquired chlamydia. Incidence rates per 100 person-years were 6.6 cases for boys and 11.9 cases for girls. In multivariable analysis, the adjusted hazard ratio was 5.34 for boys and 3.68 for girls if the student tested positive for gonorrhea during follow-up, and 2.76 for boys and 1.59 for girls if at first participation the student tested positive for chlamydia, and it increased with age among boys but not among girls. In joinpoint trend analysis, the annual percentage change in the incidence rate was 6.6% for boys (95% CI: −1.2%, 15.1%) and 0.1% for girls (95% CI: −5.3%, 5.7%). Annual cumulative incidence was 5.5% among boys and 8.6% among girls. Median incidence time was 9.7 months for boys and 6.9 months for girls. Our findings can be used to refine assumptions in mathematical modeling and in cost analysis studies of C. trachomatis infection, and provide strong evidence in support of annual chlamydia screening for adolescent boys.