Cd’A wastewater testing for COVID shows infected people in community

A recent wastewater test from the Coeur d’Alene sewage plant showed that 490 people in the city may be infected with COVID-19.

Wastewater manager Michael Anderson however said the number is based on a model that uses population size and the gallons of sewage flowing through the system, and it was determined using a very small sample size.

“That’s an alarming number,” Anderson said. “It’s still less than 1 percent (of the population).”

Panhandle Health figures show 87 cases in Kootenai County, which has a population of 166,000, while Coeur d’Alene’s population is 52,000.

The Coeur d’Alene sewage plant last month was one of hundreds nationally to use a pro bono wastewater test to monitor the prevalence of viral material coming through its system.

Anderson said although one out of the three samples taken last month and sent to a Massachusetts company called BioBot showed the existence of COVID-19, the margin of error is likely significant.

“Low numbers are considered in the noise of sampling results,” he said.

Anderson said samples, when they are in higher numbers and tested frequently, can detect trends.

“It can give a pretty good idea of what percentage of the population is infected,” Anderson said.

Testing human waste from sewage plants for the viral indicators of COVID-19 began earlier this year nationally as scientists who were already testing wastewater for the prevalence of other community indicators — including opioids — realized the tests’ potential to shed light on disease.

If wastewater samples show an increase in COVID-19 indicators, health officials could be alerted to take action to prevent an outbreak, Anderson said.

Because Coeur d’Alene tested just three wastewater samples, the results can easily be taken out of context, Anderson said.

The positive test, which came back Tuesday, from a sample taken May 25 may however warrant continuing the testing program, which was slated to end after the three initial test results were received from BioBot.

BioBot, which is based in Boston and works with researchers from universities including MIT and Harvard, according to the company, began its free testing program several months ago.

The company said it tested samples from 330 facilities in 40 states — about 10 percent of the U.S. population, during a pro bono program such as the one used by Coeur d’Alene.

According to BioBot, the SARS-CoV-2 is shed in the stool of COVID-19 patients and makes its way into sewers. The presence of infected individuals in a community can be determined by analyzing sewage.

But the number of cases are best pinpointed if sample size is large enough — usually in the thousands — and wastewater is tested often. The data can help determine when it is safe to re-open communities and businesses.

Anderson said the data can be used as an early warning system, as well as a cost-effective alternative to massive individual testing.

“It’s a neat tool to use for testing an entire population,” he said.