Health officials in several parts of the United States are seeing worrisome signals in wastewater surveillance data that the coronavirus may be spreading more widely than recent tallies of new cases would indicate, and that a steeper wave may be coming.

Wastewater surveillance provides only a broad-brush picture of virus prevalence in a particular community, but the readings it gives are close to real-time and do not depend on people seeking tests and reporting results. So health officials are looking to wastewater data for early warning of trends. And in some places, those warnings are flashing red.

The data has been like a “canary in a coal mine” for New Orleans, said Dr. Jennifer Avegno, head of the city’s health department.

More on the COVID-19 pandemic

Case counts are a “gross underrepresentation,” as many people are opting to take at-home tests instead of going to hospitals or doctors’ offices. Avegno said the rising prevalence of virus seen in wastewater testing has prompted the city to begin mobilizing resources to prepare for another spike.

Although the city is not considering reinstating mandates, it is preparing in other ways. City officials have begun planning mask giveaways and are stepping up their campaign to encourage residents to get vaccinated and boosted.

Advertising

New-case counts in the city are averaging 155 a day, five times the rate of a month ago, and wastewater tests show increased coronavirus concentrations in both residential and tourist areas.

“It looks like a surge in slow motion,” Avegno said. “It’s not the sharp increase we saw with delta and definitely not with omicron.”

Houston is another city where wastewater data has been showing ominous signs of increasing infections.

“I don’t know if it’s going to be the magnitude that we saw in the previous surge, but I definitely think we’re starting to see more community infections,” Lauren Stadler, who manages wastewater collection and analysis at Rice University, said Thursday.

Harris County, where the city of Houston is, has seen a 175% increase in cases in the last two weeks, according to a New York Times database.

Stadler said health officials in the city are trying to use the wastewater data to decide what a surge looks like these days.

Advertising

“I definitely think the wastewater is telling us it’s spreading in the community. But does that mean we’re going to see a surge in hospitals? What does that mean in terms of, like, severity of disease,” Stadler said. She added that wastewater collection also makes it hard to know who exactly is getting infected, since the data is less individualized.

Scott W. Long, medical director of diagnostic microbiology at Houston Methodist Hospital, said he hoped people would begin to take more precautions to lessen the severity of the surge in Houston.

“In my personal day-to-day, I know I’ll be masking more outside of work and while traveling,” he said.

In Maine, state health officials have been seeing a surge “for a while,” Mike Abbott, a lead analyst on wastewater screening for the Maine Center for Disease Control and Prevention, said Thursday. He noted that the increase in cases began in mid-April, with the incline getting steeper in May.

A New York Times database shows that Maine recorded a sharp upward trend in cases the last week of April and into May that reached levels the state saw during the delta surge at the end of August.

“We’ve been riding that surge,” Abbott said. “Now, as far as what’s going to happen next and what we’re worried about, I mean, certainly we’re hoping this isn’t the beginning of a surge similar to what we saw in January with the original variant.”

More

Experts maintain that the best way to combat surges and protect yourself against the virus is to be vaccinated.

“My take-home advice for people is vaccines are still our best defense. Get boosted if you’re due for one,” Long said.