The bacteria that cause chlamydia were identified in up to 88% of wastewater samples in Washington State, which supports the potential of wastewater-based epidemiology to monitor pathogens causing sexually transmitted infections (STIs), according to a new study.

STIs are not routine candidates for wastewater monitoring in the US, but their significant health burden at the national and local level has prompted interest in improving surveillance, according to corresponding author Erica Fuhrmeister, PhD, assistant professor of environmental and occupational health sciences and of civil and environmental engineering at the University of Washington, Seattle, and colleagues.

“Wastewater surveillance has grown significantly since monitoring the virus that causes COVID-19,” Fuhrmeister said. Consequently, it is feasible to explore how it can be useful for monitoring other infectious diseases, she said.

In a study published in the journal ACS ES&T Water, researchers collected two sets of wastewater samples. The large sets of 132 samples were collected weekly across five wastewater treatment plants (WWTP) in Washington State between November 2024 and February 2025. A second set of 86 samples was collected twice a month from six neighborhood-level sites in the greater Seattle area between January 2022 and June 2022.

Public Health Implications

Across the WWTP samples, Chlamydia trachomatis was the most prevalent pathogen, detected in 65%. Neisseria gonorrhoeae prevalence ranged from 0% to 11%, and Treponema pallidum prevalence ranged from 4% to 8%. At the neighborhood level, C trachomatis remained the most prevalent but less consistent, ranging from 13% to 80% prevalence across the neighborhood sites.

The researchers compared the samples with case rates for chlamydia, gonorrhea, and syphilis. Overall, detection of STIs was not associated with population size and varied across neighborhoods and WWTP locations.

The data from the neighborhood sites have the most potential to affect public health, the researchers noted. One of their examples was a neighborhood site adjacent to a college campus. The population has a high proportion of young adults aged 18-34 years, who have an increased risk for STIs. “We observed consistent wastewater detection of C trachomatis but very low clinical case counts for chlamydia,” the researchers wrote. This discrepancy may indicate underreporting of cases or a high prevalence of asymptomatic cases in the community, they said.

“I was encouraged by how seamless it was to work across different agencies and local health jurisdictions,” Fuhrmeister noted.

The study findings were limited by several factors, including the lack of data on the true shedding rates of STI pathogens into wastewater, and the relatively short time period of measurement. As a next step, the researchers are interested in looking at longer time series and focusing on college dormitories, Fuhrmeister said.

However, the results suggest that wastewater surveillance can be used to monitor for chlamydia in particular, and can be used as a tool to determine when there is higher transmission, said Fuhrmeister. “Local health jurisdictions can use that information to target resources and alert providers,” she added. Community-level interventions might include greater on-campus screening, dissemination of social marketing campaigns, and provision of self-testing kits, although demographics, disease burden, and rurality must be considered, the researchers concluded.

“Wastewater surveillance can complement, but not replace, traditional STI testing and case reporting,” said Shirin Mazumder, MD, an infectious diseases specialist and an associate professor at the University of Tennessee Health Science Center, Memphis, who was not involved in the study. The true burden of sexually transmitted infections is likely underestimated because of reasons including asymptomatic infections, stigma, limited healthcare access, and inadequate testing, said Mazumder. “Wastewater surveillance offers a way to monitor infections across communities without relying on individuals to seek testing,” she said. Use of wastewater surveillance to identify communities where infections are underdiagnosed can help direct screenings, increase self-testing, and promote education, awareness and prevention methods, Mazumder added. 

However, additional studies are needed to fully comprehend shedding patterns, pathogen instability, and the effect of wastewater variability over longer sampling periods in a variety of different community settings to better understand how to use wastewater surveillance to complement traditional STI testing, said Mazumder.

In particular, data on the duration and amount of pathogen shedding into wastewater with bacterial STIs before wastewater monitoring could be effective, she said. “Other issues in need of investigation include pathogen degradation in wastewater, and how rainfall, snow, and sewer characteristics affect concentrations,” she noted. “Monitoring smaller communities also raises privacy and stigmatization concerns,” Mazumder added.

The study was supported in part by the Epidemiology and Laboratory Capacity Infectious Diseases Cooperative Agreement from the CDC. The researchers had no financial conflicts to disclose. 

Mazumder had no financial conflicts to disclose.