Wastewater testing could soon transform how public health agencies track sexually transmitted infections, according to a study published August 7 in ACS ES&T Water. Researchers from the University of Washington and the Washington State Department of Health demonstrated that analyzing municipal sewage can effectively identify Chlamydia trachomatis, offering a population-level monitoring tool for infections that frequently go uncounted in traditional clinical settings.
How Wastewater STI Testing Works
Sick individuals shed pathogens in their waste, introducing traceable bacterial and viral genetic material into municipal sewer systems. While wastewater surveillance began with polio in the 1940s and became more widespread during the COVID-19 pandemic, American public health agencies do not routinely test sewage for sexually transmitted infections. According to University of Washington co-lead author Erica Fuhrmeister, wastewater provides a clear population-level view that bypasses the hurdles of individual clinic visits. Fuhrmeister, an assistant professor of environmental and occupational health sciences and of civil and environmental engineering, noted that STIs suffer from high rates of underreporting driven by social stigma and asymptomatic cases.
Sampling Across Urban and Rural Sites
Researchers collaborated with local health jurisdictions to collect frequent influent wastewater samples from five treatment plants across Washington state and six neighborhood-level sewer sites near Seattle. According to the study, the collection sites varied widely, spanning from a high-population urban area to a rural treatment plant serving fewer than 5,000 residents. To protect community privacy, the study masked the specific names and locations of the sampling sites. The team tested these samples for the pathogens responsible for three common infections: chlamydia, gonorrhea, and syphilis.
Chlamydia Prevalence Versus Gonorrhea and Syphilis
Laboratory results showed that C. trachomatis was the most prevalent pathogen detected across all test sites. By contrast, the bacteria responsible for gonorrhea and syphilis appeared far less frequently in the samples, despite data showing confirmed cases of those diseases in the associated areas. Researchers are currently investigating why the tests captured chlamydia much more consistently than the other bacterial pathogens, while also accounting for study limitations such as people moving between sewer sites and the influence of demographics.
Uncovering Hidden Infections Near College Campuses
One neighborhood collection site targeted a small, densely populated area adjacent to a college campus, where more than 87% of residents were young people between 18 and 34 years old—a population considered high-risk for STIs. Although traditional clinical health records showed very low case counts of chlamydia in that specific zone, researchers consistently detected C. trachomatis in the wastewater samples. According to Breanna McArdle, program manager of the Washington State Department of Health’s wastewater surveillance program, this gap could indicate underreporting. McArdle stated that such data enables public health officials to raise awareness that a pathogen is actively spreading in a community even when cases aren’t presenting to clinics or providers are not identifying the infections in their patients.
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