Sampling wastewater is nothing new. For example, at the end of 2019 scientists found a record level of cocaine in London’s sewer system, making its way to the Thames River.
Now, wastewater treatment utilities around the U.S. — including the Florida Keys — are testing sewage for traces of COVID-19.
“We took our first sample back in August,” said Dan Saus, City of Marathon utilities director.
Saus is very clear about what the laboratory tests can and cannot tell us. There’s no sci-fi magic that can trace wastewater back to a single household or person. It can, however, tell officials whether the virus is being shed into wastewater in particular neighborhoods, and whether the incidence of COVID-19 is increasing or decreasing.
Over the summer, Marathon tested five plants, five times. The tests measured two strains of COVID-19. The results were described in “copies per liter” and took two weeks to process, so the results are not available in any type of real time, Saus said.
“We have numbers. The problem is, no one has a good baseline for what it actually means,” Saus said. “I talked it over with other utilities in the Keys who are also testing, and they had the same issues.
“I discussed it with our city manager and explained that it was important to build our own baseline so that we have something to go by in the future,” Saus said.
Of all the results received, he detected only one spike. That was in early August at the treatment center in the Coco Plum neighborhood. The city recently renewed the testing contract and will begin sampling again.
Key Largo Wastewater Treatment District started tracking COVID in its wastewater back in late May and early June when a checkpoint that kept out-of-county residents away came down. Since then, the district that serves Key Largo and Islamorada has tracked the results, which have shown correlations between RNA markers in wastewater and known positive cases.
“We saw that happening when the checkpoint came down on the Stretch,” said Peter Rosasco, Key Largo Wastewater Treatment District general manager. “We saw an increase in markers in July as positive cases were increasing. Things leveled off and came down, then the infection rate went up as we started to see cooler weather up north and people coming down.”
Rosasco added they noticed a rather large increase in the number of positive cases and increase in RNA markers around the Thanksgiving holiday.
Back in April, Yale researchers in epidemiology and chemical & environmental engineering began sampling local wastewater and extracting RNA from the samples to determine the concentration of the coronavirus in wastewater. It was to assess how far the virus spread in the New Haven community.
Besides getting a more accurate estimate of the likely number of actual cases in the broader New Haven population, the applied methods may lead to an early warning system for the spread of disease in the population. Similar monitoring of wastewaters may be useful in other locales and settings as well to estimate number of corona infections in the absence of available testing of people.
“We’d like to use this data to help indicate where we are in the epidemic,” said Yale environmental engineer Jordan Peccia. “We’re also trying to find an innovative way to develop an early warning system for disease spread in the population.”
The targeted study of COVID-19 in wastewater is also conducted on university campuses. By collecting wastewater samples from distinct dorms, university officials are able to tell where the virus is spreading. At MIT, workers sampled exit pipes of several buildings. “With a dorm, a positive result could mean targeted follow-up measures like individual testing and quarantining,” according to a report from an MIT newsletter.
According to the most recent expert opinion, given good plumbing facilities, there is no evidence COVID-19 can be transmitted via stool.
*Okay, the opportunities for puns and innuendos in this story are unlimited. But we are grownups.
Jim McCarthy contributed to this report
