Sewage studies offer clues to when Omicron might fade.

Clues to how long the surge of the highly contagious Omicron might last are emerging from an unlikely source: sewage.

People who contract the coronavirus shed the virus in their stool, and the virus levels in local wastewater provide a strong, independent signal of how much is circulating in a given community.

The sewage data reveal an Omicron wave that is cresting at different times in different places.

According to Biobot Analytics, a company tracking the coronavirus in wastewater in 183 communities across 25 states, viral levels have already begun to decline in many big cities but are still rising in smaller communities.

In the Boston area, for instance, Biobot’s data suggests that the wastewater viral load has been falling since early January, consistent with other data suggesting that the virus may have peaked there. The virus appears to be waning in New York City wastewater, too, according to data shared by scientists in the region.

A variety of wastewater surveillance efforts in the United States show that viral loads have also started to decline in Denver; San Diego; Saint Paul, Minn.; and elsewhere.

Although there are lags between when wastewater samples are collected and when the results are publicly available, the most recent data suggest that the virus may not have peaked yet in parts of Ohio, Utah, Florida and wide swaths of rural Missouri.

“Wastewater surveillance is a really powerful tool, and we’re seeing really a good example of that with Omicron,” said Amy Kirby, the program lead for the National Wastewater Surveillance System, which the Centers for Disease Control and Prevention established in the fall of 2020. “It’s not just an early warning sign, but it’s also helpful to monitor the full trajectory of a surge.”

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