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Wastewater Surveillance of Chlamydia in Las Vegas Finds Peaks After Holidays, Major Sporting Events

ATLANTA – Levels of the chlamydia-causing microbe in Las Vegas wastewater increased following holidays and major events, according to an analysis presented Sunday at ASM Microbe.

Wastewater surveillance has been used to track changes in the prevalence of SARS-CoV-2 and increasingly other pathogens like influenza and RSV to inform public health officials about the state of infectious disease in the community.

Other infections, including sexually transmitted infections (STIs) like chlamydia, could also be tracked in this way, according to Avnish Mistry, a postdoc at the University of Nevada, Las Vegas. Chlamydia, which is caused by infection with Chlamydia trachomatis, is the most common STI in the US, affecting about 1.6 million people, and it can be asymptomatic among about 70 percent of infected people. As such, Mistry noted, they are less likely to seek clinical testing.

Instead, wastewater surveillance could track both people with symptomatic and asymptomatic chlamydia and guide public health interventions, Mistry said, adding that early detection is needed to prevent the development of complications like pelvic inflammatory disease among women and epididymitis among men. Current clinical screening programs are, however, expensive.

"There is a need for a cost-effective screening strategy, and wastewater treatment-based monitoring can be one of them," Mistry said during his talk.

He and his colleagues collected wastewater samples between June 2023 and March 2024 from various locations in Clark County, Nevada, which is home to about 2 million people. The wastewater catchment areas encompassed both urban and rural locations, and the urban sewersheds included the Las Vegas Strip and an airport.

After pelleting the samples, they extracted nucleic acid from the solid substrate for qPCR analysis that targeted the gene encoding the virulence plasmid protein pGP3-D to determine the presence or absence of the pathogen in the sample. This plasmid-based gene, Mistry said, is present in more than 99 percent of C. trachomatis.

He and his colleagues examined the concentration of C. trachomatis over time and overall found a rise in cases in June and then regularly identified cases after January. The prevalence of the pathogen was much higher, Mistry added, in the urban samples, and chlamydia was detected there regularly after November.

They also correlated the wastewater findings with clinically reported chlamydia cases. The wastewater-based detection of C. trachomatis in June and July was followed by a peak in clinical cases in August. Likewise, a peak of clinical cases after January was preceded by an increase in wastewater detection of C. trachomatis in November.

As Mistry noted, these trends in C. trachomatis prevalence in wastewater also themselves followed major local events: The Formula 1 Las Vegas Grand Prix took place in November, and the Super Bowl was played there in February.

"We observed higher frequency of detection after these two events that took place in Las Vegas," Mistry said. He and his colleagues similarly noted increased C. trachomatis levels after holiday periods, such as Christmas and New Year's.

The rural samples, meanwhile, had a lower prevalence of C. trachomatis, which Mistry said could be due to its smaller population. He also noted that many houses in the rural area of Clark County have septic systems and are not connected to the sewer system.

According to Mistry, his analysis shows that chlamydia can be identified through wastewater surveillance, and other STIs probably could be, as well. He suggested that, in the future, this data could be used to estimate the number of infected people within the sewershed.