The contents of St. Joseph’s sewers are helping predict COVID-19 trends in Missouri.
The City of St. Joseph is a part of a statewide sewershed project that can correlate increases in viral loads with increases in COVID-19 cases a week in advance. The data is used to inform communities of upward trends before local tests identify positive cases.
The local water protection facility was one of the first approached by the Missouri Department of Natural Resources and the Department of Health and Senior Services to participate in the study, which started in May 2020.
“The idea behind it is that you can potentially relate how many active COVID patients you have in your sewershed based on the load of COVID that we see in our sewershed,” said Katie Bruegge, the technical services manager at the St. Joseph water protection facility.
Now, more than 85 cities send in weekly sewer samples for the project. But local water protection facilities are just the first step in the process, which is as follows:
1) Water protection facilities across the state extract weekly samples from wastewater and send them to the University of Missouri for testing.
2) Scientists extract and analyze the viral genetic material from the samples.
3) An analyzer measures the viral load in each sample using a polymerase chain reaction. This is a similar test to a nasal swab.
4) Viral load results are then calculated based upon the number of viral markers per liter of wastewater and the flow rate at each water treatment facility when the sample was taken.
The lab calculates the moving average of the number of viral markers per day to identify COVID-19 trends in a community.
“Looking at those viral loads and the number of virus particles that we’re seeing in the sewershed, we were able to correlate that with case counts in communities to see if there was some sort of pattern or trend,” said Jeff Wenzel, the chief of the Bureau of Environmental Epidemiology within the Missouri Department of Health and Senior Services.
For example, St. Joseph has experienced a downward trend in viral loads since the beginning of August. This directly correlates to a decline in cases and hospitalizations during that time.
Once new variants were detected across the country, the DHSS added a wrinkle to its project. In February, it began testing for variants.
“We look at a smaller section of the RNA, where a lot of these unique mutations are occurring,” Wenzel said. “That gives us an indication of what mutations or what variants are present in that community.”
The earliest “probable” detection of a variant in the St. Joseph water protection was May 3, according to the samples. Starting May 31, the alpha and delta variants were “presumed” to be in the community.
The viral load and variant tests aren’t foolproof, but based on past results the predictive trends have been accurate.
“A significant increase in viral load is also followed by a significant increase in known human cases at least 70% of the time, so we were very accurate as far as being predictive in those trends,” Wenzel said.
St. Joseph’s current positivity rate for COVID testing is at 8.17% as of Thursday, according to the St. Joseph Health Department. Officials reported 52 new cases of the virus since Tuesday, and 18 people are hospitalized at Mosaic Life Care for COVID.