The Contact Tracing Collaborative developed a traffic light system to alert the public of COVID-19 risk levels. Most recent wastewater testing data has the four municipalities in the yellow or “moderate” risk zone. Contributed Image

The Greenfield Water Pollution Control Facility off Deerfield Street in Greenfield. Staff File Photo/Paul Franz

Editor’s note: The Greenfield Recorder has been providing regular updates on the risk level of COVID-19 transmission as wastewater testing results are received.

With a spike in the volume of virus copies in area wastewater receding, the risk for COVID-19 has dropped to “moderate” in the four communities involved in the Contact Tracing Collaborative, which consists of Greenfield, Deerfield, Montague and Sunderland.

“It’s trending in the right direction at the moment,” said Deerfield Board of Health Chair Carolyn Shores Ness. “We had a little surge just like we predicted and we anticipate another surge when people get together over Thanksgiving and the holidays.”

Virus concentration in Greenfield’s wastewater decreased from approximately 2.4 million copies of virus per liter of sewage to 1.2 million copies per liter between Oct. 19 and Oct. 26, according to data from Biobot Analytics.

Cluster events (infections of three or more people at one site) were down to six, compared to 10 in the week prior. Hospitalizations were down across the four communities as well, with the daily average down to 2.25 from 2.71.

With positive tests left unreported or people not testing for the virus at all when they’re sick, Shores Ness said communities are often left with only the ability to react to wastewater numbers and clusters.

“We’re basing it on clusters and the wastewater mostly. The number of cases are inaccurate,” Shores Ness explained. “We’re monitoring as carefully as possible.”

Heading into the winter, Shores Ness said public health officials will be keeping an eye on the BQ1 and BQ1.1 omicron subvariants, which have been increasingly spreading across New England, according to the most recent Centers for Disease Control and Prevention data.

“If you have had your booster, you have some ability to fight those,” Shores Ness said. “This could be a tough winter and we’re doing everything we can to be on top of it.”

With wastewater and cluster numbers where they currently stand, the Contract Tracing Collaborative communities are now in the yellow zone with a moderate risk of COVID-19 transmission, with masking encouraged.

In combination with wastewater testing — people with an active COVID-19 infection excrete the virus in their stool, and samples from wastewater treatment plants can be analyzed to estimate community virus levels — the four municipalities factor in hospitalization numbers, positivity rates and case numbers to determine risk levels. Health officials also continue to talk with nursing homes, businesses and schools to track cluster infections.

The following three zones, defined by the Contact Tracing Collaborative, are used to gauge risk levels of COVID-19 transmission in the four communities. For the risk level in the area to change, at least two measures need to apply.

■Cluster infections (of three or more people at one site): five or more.

■Percent positive tests out of total tests performed: greater than 10%.

■One to four cluster infections.

■Decreased virus copies in wastewater.

Chris Larabee can be reached at clarabee@recorder.com or 413-930-4081.

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