A city's sewers say a lot about its residents. Sick people often shed pathogens in their waste, adding traceable amounts of bacteria and viruses into wastewater. Testing that wastewater offers a simple, low-cost way to monitor the spread of disease — a practice that began with polio in the 1940s and became more widespread during the COVID-19 pandemic. Today, the CDC's wastewater monitoring program tests for a variety of common and emerging viruses.
American public health agencies don't routinely test wastewater for sexually transmitted infections, but new research led by the University of Washington and the Washington State Department of Health found that such methods could be used to effectively identify Chlamydia trachomatis, the bacteria that causes chlamydia.
The study, published Aug, 7 in ACS ES&T Water , could help public health agencies better identify and respond to increased spread of chlamydia and other STIs, which are notoriously underreported in traditional data. The researchers specifically explored wastewater's potential as a community monitoring tool, and not as a way to identify cases or trace pathogens back to individual people or locations.
"STIs are known for being underreported because of a lot of factors, especially stigma and the prevalence of asymptomatic cases," said co-lead author Erica Fuhrmeister , assistant professor of environmental and occupational health sciences and of civil and environmental engineering at the UW. "Wastewater is cool because it's population level. You don't need people to go to the doctor and seek out treatment to know that there are people in a community shedding specific pathogens."
Working in collaboration with local health jurisdictions, researchers collected frequent samples from influent wastewater at five wastewater treatment plants across Washington state and six neighborhood-level sewer sites near Seattle. Collection sites ranged from a large, high-population urban area to a rural treatment plant serving fewer than 5,000 people. Researchers masked the specific names and locations of sample locations to protect the privacy of people and communities.
Researchers tested wastewater samples for the pathogens that cause three common STIs: chlamydia, syphilis and gonorrhea. C. trachomatis was the most prevalent pathogen across all test sites. The bacteria that cause gonorrhea and syphilis were found far less frequently, despite data showing confirmed cases of those diseases in the associated areas.
Further research could reveal why tests captured C. trachomatis more consistently than other STI-causing bacteria and explore the study's limitations, which included people moving between sewer sites and the influence of demographics.
The researchers are also eager to investigate several trends they observed in the data, such as spikes in pathogen concentration occurring near the winter holidays and after Valentine's Day.
Among the neighborhood collection sites was a small, densely populated area adjacent to a college campus. More than 87% of residents were young people between 18 and 34 years old, a population considered high-risk for STIs. Clinical health records showed very low case counts of chlamydia, but researchers consistently detected C. trachomatis in wastewater samples.
That gap could indicate underreporting driven by stigma or asymptomatic cases. It also gives public health officials an opportunity to react to a previously unknown increase in infection activity.
"From a public health perspective, data like this allows us to elevate awareness that this pathogen is here and spreading in the community, even if cases aren't presenting to clinics or providers are not identifying the infections in their patients," said co-lead author Breanna McArdle , program manager of the Washington State Department of Health's wastewater surveillance program. "A small amount of wastewater can tell you so much about the community while simultaneously filling gaps in the traditional methods we monitor disease activity."
A full list of co-authors is available with the paper.
This research was funded in part by the Epidemiology and Laboratory Capacity Infectious Diseases Cooperative Agreement from the U.S. Centers for Disease Control and Prevention.
