Background:
High prevalence of infection with Chlamydia trachomatis in Philadelphia teens led to the introduction of system-wide urine-based screening in the city's public high-schools in 2002-03. Prevalence in teens has declined since screening was introduced.

Objective:
To assess the cost-effectiveness of the Philadelphia high-school Chlamydia screening program, using a dynamic transmission model. Transmission is not taken into account in most existing cost-effectiveness analyses of Chlamydia screening.

Method:
A transmission model was constructed using cross-sectional prevalence data, based on the simplifying assumption that the Philadelphia Chlamydia epidemic was at equilibrium when screening was initiated. Data on test costs were derived directly from the screening program; costs of complications of infection (e.g., pelvic inflammatory disease, infertility, etc.) were abstracted from the published medical literature.

Result:
The model reproduced observed changes in population prevalence of Chlamydia that occurred after screening was introduced. Screening both males and females resulted in a greater reduction in pelvic inflammatory disease and related sequelae than screening either gender alone. All screening strategies (including screening only males) resulted in net cost-savings relative to no screening, but the greatest savings were seen when both genders were screened. Screening was cost-saving even when initial prevalence in females was as low as 3%, but the number of years required to “break even” financially increased as prevalence declined.

Conclusion:
Chlamydia screening in Philadelphia public high-schools is projected to result in large net societal cost-savings. Cost-savings associated with Chlamydia screening are projected to be greatest when programs target both male and female students, rather than just females. Screening is projected to be cost-saving at relatively low prevalence thresholds when transmissibility is taken into account.

Implications:
Dynamic transmission models for the economic evaluation of Chlamydia control programs results in more realistic model projections, and permits identification of the economic benefits associated with screening males as well as females.