Sexually Transmitted Infection Wastewater-Based Surveillance in Rural and Urban Washington State

Abstract

Much like the microbes in our guts, sexually transmitted infections (STIs) have been with humans for as long as we can remember, and impact millions of people each year around the globe – as they have for millennium. In Washington State, cases of Neisseria gonorrhoeae (gonorrhea), Chlamydia trachomatis (chlamydia), and Treponema pallidum (syphilis) are on the rise and impacting the health of communities. Stigma and asymptomatic infections make it difficult to have representative case data of STIs due to underreporting at the clinical level. In this study, we surveilled N. gonorrhoeae, C. trachomatis, and T. pallidum in wastewater influent in Washington state. We collected twice weekly samples from five different wastewater treatment plants across Washington state, representing urban and rural communities, between November 2024-February 2025. Solids were separated from wastewater using centrifugation and DNA was extracted using a modified AllPrep Powerviral DNA/RNA (Qiagen) protocol. To quantify our three targets, we developed a triplex digital PCR (dPCR) assay for all three STI targets. We identified C. trachomatis at all five locations and in 65% (86/132) of total samples. Of the five surveyed systems, one location (WWTP WA5) is an adequate candidate for continuing wastewater-based epidemiology for C. trachomatis, with 87.5% (21/24) samples positive for C. trachomatis compared to 41.7-70.8% positive in other locations. Wastewater surveillance data on N. gonorrhoeae, C. trachomatis, and T. pallidum can inform interventions and actions by local health jurisdictions as well as college campuses. Potential responses include targeted campaigns to encourage STI testing and treatment. Additionally, wastewater surveillance can benefit rural communities in WA where STI stigma and barriers to healthcare are more common.