From the Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
Epidemiology. 2013 Nov;24(6):854-62. doi: 10.1097/EDE.0b013e31829e110e.
Pelvic inflammatory disease (PID) results from the ascending spread of microorganisms, including Chlamydia trachomatis, to the upper genital tract. Screening could improve outcomes by identifying and treating chlamydial infections before they progress to PID (direct effect) or by reducing chlamydia transmission (indirect effect).
We developed a compartmental model that represents a hypothetical heterosexual population and explicitly incorporates progression from chlamydia to clinical PID. Chlamydia screening was introduced, with coverage increasing each year for 10 years. We estimated the separate contributions of the direct and indirect effects of screening on PID cases prevented per 100,000 women. We explored the influence of varying the time point at which clinical PID could occur and of increasing the risk of PID after repeated chlamydial infections.
The probability of PID at baseline was 3.1% by age 25 years. After 5 years, the intervention scenario had prevented 187 PID cases per 100,000 women and after 10 years 956 PID cases per 100,000 women. At the start of screening, most PID cases were prevented by the direct effect. The indirect effect produced a small net increase in PID cases, which was outweighed by the effect of reduced chlamydia transmission after 2.2 years. The later that progression to PID occurs, the greater the contribution of the direct effect. Increasing the risk of PID with repeated chlamydial infection increases the number of PID cases prevented by screening.
This study shows the separate roles of direct and indirect PID prevention and potential harms, which cannot be demonstrated in observational studies.
盆腔炎性疾病（PID）是由微生物（包括沙眼衣原体）上行性扩散至生殖器官上部引起的。筛查可以通过在衣原体感染进展为 PID 之前（直接作用）识别和治疗，或通过减少衣原体传播（间接作用）来改善结局。
我们开发了一个房室模型，代表一个假设的异性恋人群，并明确纳入了从衣原体到临床 PID 的进展。引入了衣原体筛查，每年筛查覆盖范围增加 10 年。我们估计了筛查对每 10 万女性预防 PID 病例的直接和间接作用的单独贡献。我们探讨了改变临床 PID 发生时间点和增加反复衣原体感染后 PID 风险对结果的影响。
基线时，25 岁以下女性发生 PID 的概率为 3.1%。5 年后，干预方案预防了每 10 万女性 187 例 PID，10 年后预防了每 10 万女性 956 例 PID。在开始筛查时，大多数 PID 病例是通过直接作用预防的。间接作用产生了一个小的 PID 病例净增加，这被 2.2 年后减少的衣原体传播的影响所抵消。PID 进展到临床 PID 的时间越晚，直接作用的贡献就越大。增加反复衣原体感染后 PID 的风险会增加筛查预防的 PID 病例数量。
本研究表明了 PID 预防的直接和间接作用及其潜在危害的分离作用，这在观察性研究中无法证明。
