Modeling the impact of treatment failure on Chlamydia transmission and screening

Standard current treatment regimens for chlamydia treatment have been widely considered to be highly effective, with a cure rate of around 97%. However, recent studies indicate that treatment failure may occur at a rate that is substantially higher than previously thought.

We use a mathematical dynamic transmission model to estimate the population-level impact of treatment failure on chlamydia transmission and on the effectiveness of screening strategies.

The findings indicate that in high-resource settings such as Australia, there will be an approximately 0.16% linear increase in population prevalence for each incremental increase of 1% in the treatment failure rate. To compensate for higher assumed treatment failure, screening coverage will have to increase by between ∼4% and ∼16% to achieve a reduction of 50% in chlamydia prevalence within 5 years under the scenarios evaluated. Higher treatment failure rates also substantially lengthen the time required for screening to deliver the same reductions in prevalence as are predicted under the conservative assumption of only 3% treatment failure. The predicted relative increases are in the range ∼6% to 35%, depending on the assumed treatment failure rate (8%-23%), screening strategy (female-only or male-plus-female) and the duration of screening (5 or 10 years).

The rate of treatment failure may have a significant impact on the screening coverage and time required to achieve target reductions in chlamydia prevalence. The treatment failure rate should therefore be carefully considered when evaluating the potential effectiveness of proposed screening programs.