As the highly contagious omicron variant pushes national coronavirus case numbers to record highs and sends hospitals across the country into crisis mode, public health officials are eagerly searching for an indication of how long this surge might last.

The clues 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 US show that viral loads have also started to decline in Denver, San Diego, Saint Paul, Minnesota 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 swathes 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 programme 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.”

Over the course of the pandemic, scientists, health officials and biotech companies have been building wastewater surveillance systems that they hoped would spot new variants, track the spread of the virus and provide advance notice of coming surges.

“It’s a type of data that we are all creating, naturally, organically, when we are using the restroom,” Mariana Matus, the chief executive and co-founder of Biobot Analytics, said.

The CDC, which is now funding sewage surveillance efforts in 43 states, cities and territories, plans to add wastewater data to its online “Covid Data Tracker” within the next few weeks, Dr Kirby said. And the agency is in the process of adding about 500 testing sites across the country to its surveillance system.

Wastewater surveillance is already informing local pandemic responses. City officials are using it to funnel resources into neighbourhoods where the virus is surging, and hospitals are using it to make life-or-death decisions.

But these efforts remain spotty and ad hoc, confined to places where good data is easily accessible and local officials are interested in using it. The USneeds to do more to expand and coordinate these efforts and to make more data available faster, experts said. There is still no centralised public dashboard where all of the nation’s wastewater data is collected and displayed.

(New York Times News Service)