Every Tuesday and Thursday morning, employees at the Haskell R. Street Wastewater Treatment Plant in Central El Paso fill a 250-milliliter plastic bottle with sewer water.
They label it with a barcode, carefully pack it up using gel ice packs to keep the wastewater cold, and ship it to a laboratory to be analyzed for the presence of the SARS-CoV-2 coronavirus.
The practice is part of the city’s new wastewater surveillance efforts, a technology that has emerged as a key tool for early detection of COVID-19 community spread.
“Surveillance helps us prepare for what might be coming,” said Angela Mora, the city’s public health director.
Mora played a key role in enrolling El Paso in the Centers for Disease Control and Prevention’s National Wastewater Surveillance System, and she plans to expand local wastewater surveillance in the future to track other diseases.
When people are infected with a virus, that virus is shed in the stool — even when the person is pre-symptomatic or asymptomatic — according to Nour Sharara, a wastewater analysis expert and public health scientist for Boston-based Biobot Analytics, a company that specializes in wastewater monitoring.
Sharara said a wastewater sample is tantamount to a “community wide stool sample,” making it an excellent measure of how much virus is circulating within the community. Its usefulness is even greater because it bypasses the lag time of other measures of local community spread, such as positive test results and hospitalization rates.
“(Wastewater surveillance) gives this early warning signal to the health care system saying, ‘Look, the levels of COVID are going up. That means that in a few days, we’re gonna have more cases and in a few weeks more hospitalizations,’” she said. “It has been consistently a leading indicator of cases and hospitalizations and death.”
In January, El Paso became one of 600 cities participating in the CDC’s national surveillance system. Through the program, the city sends two wastewater samples per week from each of El Paso’s four wastewater treatment plants to a contractor that tests the sample for COVID-19.
The CDC then analyzes the data and provides regular reports to city officials.
Since the analysis began in January, the highest increase in COVID-19 levels present in wastewater happened in February, followed by a drop in early to mid-March, according to city spokesperson Laura Cruz Acosta. As of April, low virus levels in wastewater have been stable.
The CDC routinely will alert local officials if they are observing any noteworthy trends in wastewater data, said Brian Katzowitz, a health communications specialist at the CDC.
“A few things we look for are sustained increases in wastewater levels over time, geographic clustering (sites all reporting increases in a concentrated geographic area), and what’s happening in the community that could be impacting the data (tourism, a big event, changing masking guidance, etc.),” Katzowitz wrote in an email to El Paso Matters.
Although the wastewater surveillance contract with the CDC lasts for one year, the city will conduct its own wastewater testing eventually, Mora said. She pointed to the sprawling new facility that houses the city’s public health department, a former Boeing warehouse in Northeast El Paso, and described plans to expand wastewater testing capacity, not only for COVID-19 but also for other pathogens.
As norms around testing have changed with more people using at-home COVID-19 tests that may not be reflected in local case counts, Mora said the usefulness of wastewater surveillance is even greater.
She said the potential future applications of wastewater testing are wide ranging.
“Let’s say that we were concerned with another condition in a specific area, you could do a wastewater surveillance of a school or a jail so that you can determine certain activity of certain pathogens in specific areas,” Mora said.
In the near future, the public health department is working to add a map feature to the city’s online COVID-19 dashboard to help El Pasoans understand wastewater surveillance data. A link to the CDC’s wastewater surveillance interactive map (containing data for El Paso County) is currently on the city’s main COVID-19 data page, though wastewater data has not yet been incorporated into the city’s dashboard, nor is it included in the city’s weekly COVID-19 reports.
Sharara said wastewater surveillance data is not only a useful analytical tool for city leaders, but has proven to be an important community resource. She cited how residents of Boston — which has been testing wastewater since 2020 — responded to wastewater data during the early days of the omicron surge in December 2021. She said that there was a local response to the dramatic upward curve in wastewater COVID-19 levels even before it had been reflected in local testing and hospitalizations.
“We know that some people, for instance, canceled indoor gatherings,” she said. “It was around Christmas, people had Christmas parties (that they canceled)… So the community data is not only useful for the city, it’s also useful for the people who live and work in those communities, it helps them do a community risk assessment and inform the decisions that they can take.”
Wastewater testing will continue to grow in importance in the coming years, according to Sharara.
“We’re still only two years into the pandemic, there’s still so much we need to learn about this virus,” she said.
Although the CDC program is not currently analyzing El Paso’s wastewater for specific COVID-19 variants, Sharara said variant tracking is an increasingly useful application of wastewater monitoring.
“In some communities in the U.S., we were able to find omicron in wastewater before it was reported by a clinical lab — because they had to wait for someone to get sick, to get tested, to get the results, to do genomic sequencing on it. All this time, that wastewater can just sort of fast forward.”