Time from sexually transmitted infection acquisition to pelvic inflammatory disease development: Influence on the cost-effectiveness of different screening intervals

Objectives: To prevent pelvic inflammatory disease (PID), some experts recommend screening for sexually transmitted infection (STI) every 12 months, with more frequent screening suggested in higher-risk women. Nevertheless, the time from STI acquisition to PID development, possibly an important factor to consider in screening interval choice, is unknown and its influence on the effectiveness and cost-effectiveness of screening is unclear. Methods: Using a Markov model, we estimated PID cases averted and the incremental cost-effectiveness resulting from 6- or 12-month screening strategies for high-risk young women (6%/year infection risk, 2.8%/year PID risk with 12-month screening) while varying PID development time from 1 to 12 months after initial infection. Lower-risk women and alternative parameter values were examined in sensitivity analyses. Results: Relative to 12-month screening, 6-month screening decreases PID cases from 6.0% (1 month development time)to 19.4% (12 months); the incremental cost per quality-adjusted life-year (QALY) gained compared with the other strategies varies from $16,600 (12 months development time) to $31,800 (1 month) for high-risk women. In lower-risk women, every 6-month screening is more economically unfavorable, with greater costs per QALY gained at shorter PID development time. Conclusions: From a cost-effectiveness standpoint, uncertainty about PID development time is not a significant factor in choosing a screening interval in high-risk women, but could be important in lower-risk groups. Significant increases in PID cases averted occur with more frequent screening when PID development time is lengthened, which may allow estimation of this interval through the use of more sophisticated modeling techniques.