A published mathematical model of chlamydia transmission (Fisman, et al. 2008, see 'Other Publications of Related Interest' below for bibliographic details) was used to synthesise the evidence. The model had five age groups; 10 to 14, 15 to 19, 20 to 24, 25 to 29, and 30 to 39 years. The time horizon was 18 years, from 1991 to 2009. The authors stated the study took a modified societal perspective, which excluded people's time and travel costs.
The key outcomes were the probabilities of symptomatic infections, pelvic inflammatory disease with or without symptoms, and complicated chlamydia infections in men. The inputs for prevalence, transmission, complications and natural clearance of chlamydia infection were from epidemiological studies. The chlamydia testing volumes over time were from Ontario’s public health laboratory system. The model was calibrated using the age-specific prevalence of chlamydia infections in Canada from 1991 to 2009.
Monetary benefit and utility valuations:
Pelvic inflammatory disease was assumed to result in a loss of about one quality-adjusted life-year (QALY), due to infertility and chronic pelvic pain, based on a published study of patients with the disease.
Measure of benefit:
The summary benefit measures were QALYs, symptomatic infections, cases of symptomatic pelvic inflammatory disease, and chronic sequelae averted. Future benefits were discounted at 3% per year.
The direct costs included those of the screening tests, treatments, and complications, such as epididymo-orchitis, tubal infertility, and ectopic pregnancy. The resource use for antimicrobial therapy, adverse drug reactions, and doctor visits was from published studies. Prices were adjusted for inflation to 2009 values, using the personal care component of the Canadian Consumer Price Index. All costs were reported in Canadian dollars (CAD) and future costs were discounted at 3% per year.
Analysis of uncertainty:
One-way, and probabilistic (using 1,000 simulations) sensitivity analyses were performed. The results were illustrated in a tornado graph, a scatter plot, and cost-effectiveness acceptability curves.