Environmental tobacco smoke exposure and pelvic inflammatory disease: a cross-sectional analysis of serum cotinine

BACKGROUND: Pelvic inflammatory disease (PID) is a common gynaecologic condition linked to infertility, ectopic pregnancy, and reproductive tract cancers. While active smoking has been associated with PID, the impact of environmental tobacco smoke (ETS) on non-smoking women remains unclear. Most studies rely on self-reported exposure, which may be inaccurate. Cotinine, a stable nicotine metabolite, serves as an objective biomarker of tobacco exposure. This study investigated the association between serum cotinine levels and PID risk in non-smoking women using data from the National Health and Nutrition Examination Survey (NHANES). METHODS: This cross-sectional study included 3,718 non-smoking women aged ≥18 years from NHANES 2013-2020. ETS exposure was assessed using serum cotinine measured by isotope dilution high-performance liquid chromatography with tandem mass spectrometry. Cotinine levels were categorised as unexposed, low, or high exposure. PID was identified based on self-reported treatment for pelvic infections. Weighted logistic regression was used to examine associations between cotinine and PID, adjusting for confounders identified by a directed acyclic graph. Restricted cubic spline and subgroup analyses were also conducted. RESULTS: -transformed cotinine was associated with a 10% increase in PID risk (OR = 1.10; 95% CI: 1.02-1.19). High ETS exposure (≥3 ng/mL) was linked to a significantly higher risk of PID compared to unexposed individuals (OR = 2.53; 95% CI: 1.05-6.08). A linear dose-response relationship was observed. Subgroup analyses showed consistent results across all strata. CONCLUSION: Serum cotinine-defined ETS exposure was significantly associated with increased PID risk in non-smoking women. Reducing ETS exposure may help prevent reproductive tract infections.