Wastewater STI Monitoring Could Catch Outbreaks Early

Public health may have a new place to look for sexually transmitted infections: the sewer. A study out of the University of Washington this week found the bacteria behind chlamydia in most wastewater samples taken across Washington State, and the results suggest wastewater STI monitoring could spot outbreaks that official case counts miss. STIs are not currently part of routine wastewater surveillance in the United States, but the team argues the country's existing sewer-monitoring network, built up during the COVID pandemic, makes the idea practical. According to Medscape, which reported the findings, the peer-reviewed study was published in the journal ACS ES&T Water.

The research team was led by Erica Fuhrmeister, an assistant professor of environmental and occupational health sciences and of civil and environmental engineering at the University of Washington in Seattle. The group collected two sets of samples. One set of 132 samples came from five wastewater treatment plants across Washington State between November 2024 and February 2025, drawn every week. The other set of 86 samples came from six neighborhood-level sites around the Seattle area, sampled twice a month from January to June 2022.

What showed up in the water

Chlamydia trachomatis, the bacterium that causes chlamydia, turned up more often than any other pathogen the team tested for. It appeared in 65% of the treatment-plant samples. At the neighborhood sites, detection swung from 13% to 80% depending on the location. The bacteria behind gonorrhea showed up in 0% to 11% of samples, and the syphilis bacterium in 4% to 8%. The researchers checked their wastewater results against clinical case rates for the three infections and found the two did not always line up: detection had little to do with population size and varied a lot from one neighborhood to the next.

The most telling mismatch sat next to a college campus. One neighborhood sampling site served an area with a high share of young adults aged 18 to 34, the age group most at risk for STIs. The wastewater there kept testing positive for chlamydia while the official case counts stayed low. The researchers wrote that the gap points to underreporting or a large number of asymptomatic infections circulating without anyone knowing. Rising STI rates are not just a local story either. Syphilis is rising fast in Australia, especially among women, driven by gaps in testing and awareness.

Why health departments want this

If sewers can flag where transmission is running hot, local health departments could aim their resources at those neighborhoods instead of guessing. The study authors suggested the data could prompt more on-campus screening, targeted social marketing campaigns, and wider distribution of self-testing kits. Fuhrmeister said local health jurisdictions could use the information to target resources and alert providers when transmission climbs. Faster, lower-friction testing is already reshaping sexual health care. Twenty-minute STI tests could end Australia's days-long wait for results, showing how quickly the field is moving toward answers in a single visit.

The approach borrows from the COVID playbook. Wastewater surveillance grew enormously while tracking the virus behind the pandemic, and the sampling infrastructure, lab pipelines, and reporting dashboards from that era are still in place. According to Medscape, Fuhrmeister said: "Wastewater surveillance has grown significantly since monitoring the virus that causes COVID-19. Consequently, it is feasible to explore how it can be useful for monitoring other infectious diseases." The study was supported in part by a cooperative agreement from the Centers for Disease Control and Prevention, a sign that federal public health agencies are taking the idea seriously.

There are real caveats. The researchers do not yet know the true rate at which STI pathogens shed into wastewater, and the sampling windows were short. Their next step is a longer time series with a focus on college dormitories. Shirin Mazumder, an infectious diseases specialist and associate professor at the University of Tennessee Health Science Center in Memphis who was not involved in the study, told Medscape that wastewater surveillance can complement but not replace traditional testing. According to Mazumder, the true burden of STIs is likely underestimated because of asymptomatic infections, stigma, limited healthcare access, and inadequate testing. Mazumder also flagged a thornier issue: monitoring smaller communities raises privacy and stigmatization concerns, and researchers still need better data on how pathogens degrade in wastewater and how rain, snow, and sewer design shift concentrations.

For now the takeaway is concrete. Clinics only see the people who walk through the door. Sewers see everyone. If the open questions about shedding rates get answered, wastewater STI monitoring could join the standard toolkit that tells public health officials where to look next.