CARMEL, Ind. — Thousands of COVID-19 cases are emerging in the Hoosier state every day, and one method of testing for the virus is providing even more insight into its prevalence in the community.
The City of Carmel is one of only a handful of municipalities in the state conducting wastewater testing for the coronavirus disease, a tool that has proven successful as an early method of detection for other diseases like polio.
Since May of 2020, the city has been collecting samples on an average of two times per week at the Carmel Wastewater Treatment Plant and analyzing it for the presence of RNA from SARS-CoV-2, the virus that causes COVID-19 infections.
“The idea early on was sort of like an early warning system. I think it is, but it has more evolved into I think a real good confirmation of what’s going on,” said John Duffy, Utilities Director for City of Carmel Utilities.
“We also wanted to be a part of kind of a national effort. There’s many, many places that are now sampling for Covid in wastewater, so we wanted to be a part of that and learn,” Duffy added.
The CDC explains that the virus can be shed in the waste of people who are both symptomatic or asymptomatic with infection, which is how wastewater surveillance can capture data on both types of infections.
“It is a known fact that viruses can be detected when people shed. The virus that we’ve seen, it can be shedding different times, and different loadings and that’s kind of the fascinating part of it,” said Duffy.
Not everyone will get a Covid test, but everyone goes to the bathroom, therefore health officials said wastewater surveillance can provide a snapshot of the prevalence of disease in the community.
Because everyone sheds the virus differently, the concentration of RNA from SARS-CoV-2 in wastewater is essentially treated as an average to get an idea of what is going on in the community.
How does the testing and analysis process work?
“Our wastewater treatment plant staff, or lab staff in particular, we have what’s called a composite sampler and it pulls a portion of the sample on an hourly basis over 24 hours and all of those smaller samples are combined into one and they’re shipped off to Biobot, which is in Boston,” said Duffy.
“One sample tests a wide range of people,” he added.
The samples are shipped overnight to the lab in Massachusetts for analysis and Duffy said they typically receive the results in about two to three days.
“It kind of really highlights in a good way that wastewater treatment plants can be used — I mean there’s another sort of side benefit,” said Duffy. “There’s an analytical tool that can be used. In this case, it’s for Covid.”
Since the city began its surveillance testing at the wastewater plant, Duffy said the results they have been getting have followed the trend of positive cases in Hamilton County.
“Throughout, that’s been consistent,” said Duffy. “It’s been a real confirmation of what’s going on. It confirms in some respect what they already know.”
The city shares its COVID-19 dashboard, with wastewater treatment results updated as they receive them.
“The most recent wave with omicron, or even before omicron, I think really we started to see a spike in early December which has continued and really got high, as high as we’ve ever seen it, in the Christmastime period,” said Duffy.
The most recent three samples, however, are showing a glimmer of hope that the amount of the virus in the community could be on the decline.
Duffy said, “Our most recent three samples, though, the trend is down it’s declining roughly 38% from the previous three samples.”
“What the testing is showing is there is a considerable amount of virus out there, compared to other time periods, but that it is not as high as what we were seeing it has come down,” he explained.
Does this mean the spread of the omicron variant is past its peak? It may still be too soon to tell.
“When we see it declining, that’s always a good thing. We’ve kind of learned over time don’t get too excited one way or the other with one sample.”
That’s because Duffy said it usually takes a third sample to give them an idea of any change in trends. Still, he said any decline is a hopeful sign.
The testing has provided more than just insight into the spike or decline in cases, but also the viral load that each strain carries, said city staff.
“When Delta came our results spiked quite a bit and one of the things that we learned is Delta was more prevalent, that the concentration in and of itself, it was more prevalent and it’s spiked, but the amount of cases, we would have thought there would have been more,” said Duffy. “Cases went up as well, but it was more concentrated so we see it.”
“Then you have omicron, which they are able to detect and that has gone to another level,” said Duffy.
Duffy said wastewater testing is a tool he’s glad the city is using to track the disease in the community.
“It is a tool. It is a confirmation tool. I don’t know if you would want to use it for setting policy, like ‘oh we got our test it went way up we need to shut down schools,’ I don’t think that’s what we’re talking about,” said Duffy.
He also said it isn’t taking them away from work they’re already doing, but instead adding another layer to the puzzle of understanding the evolution of COVID-19 and its prevalence in Carmel.
“We don’t want it to take away from all of the other things we have to do. We want to make it part of that but not to the point where it’s a burden,” said Duffy.