Incidence of Infections with Chlamydia Trachomatis Among High School Students

Background:  Infections with Chlamydia trachomatis are highly prevalent among adolescents, but their incidence has not been well studied.

Objectives:  To determine the incidence of C trachomatis infections in an initially chlamydia-free high school student population.

Methods:  Between 1995 and 2007, 7990 students in an urban US high school district were tested for C trachomatis more than once in an annual school-wide screening using urine DNA amplification tests. Students testing positive were treated with 1g azithromycin orally under direct observation. Incidence rates were calculated among 7292 students (Females: 3506; Males: 3786) aged 14 to 19 at their first participation in screening.

Results:  The average annual cumulative incidence was 5.4% among males and 8.8% among females (p<.0001). The average incidence rate was 6.5/100 person-years (p-yrs) for males and 11.4/100 p-yrs for females (p<.0001). The incidence rate was 8.2/100 p-yrs among students whose test result at first participation was negative compared with 23.8/100 p-yrs among students whose test result at first participation was positive (p<.0001). Among students whose test result at first participation was negative, the median incidence time from the date of their initial negative test was 10.0 months for males and 9.5 months for females. Among students whose test result at first participation was positive, the median incidence time from the date of treatment was 6.5 months for males and 5.6 months for females.

Conclusions:  While these incidence rates, cumulative incidence, and incidence times support current recommendations for annually screening female adolescents for chlamydia, they also provide strong evidence in support of annual chlamydia screening for male adolescents.

Implications for Programs, Policy, and Research: Female as well as male adolescents should be tested annually for sexually transmitted chlamydial infection. Greater access to STD screening in high schools should be a public health priority in the US.