It may be time to dust off the face masks and air purifiers.

The US is in the midst of a significant Covid-19 wave, with viral activity levels in wastewater the highest they’ve been for a summer surge since July 2022, according to the US Centers for Disease Control and Prevention’s wastewater dashboard.

The CDC’s measure of national Covid viral activity in wastewater rose to 8.82 on August 10 – falling shy of a peak of 9.56 in July 2022. The CDC says the most recent data is incomplete and may change. Before it started rising again in May, it was at 1.36.

“Currently, the COVID-19 wastewater viral activity level is very high nationally, with the highest levels in the Western US region,” Dr. Jonathan Yoder, deputy director of the CDC’s Wastewater Surveillance Program, said in an email. “This year’s COVID-19 wave is coming earlier than last year, which occurred in late August/early September.”

Emergency room visits, hospitalizations and deaths are also ticking up, although not to the same extent as infections, according to the CDC’s Covid dashboard. As of the end of July, the CDC’s dashboard shows about 4 are being hospitalized for Covid for every 100,000 people in a given area, up from a low in May of about one Covid hospitalization for every 100,000 people – the lowest level since the pandemic began.

The CDC’s wastewater data closely aligns with what they’re seeing at the nationwide WastewaterSCAN network, too.

“This is a very significant surge. The levels are very high. They’re the highest we’ve ever seen during a summer wave,” said Dr. Marlene Wolfe, an assistant professor of environmental health and public health at Emory University and a program director for WastewaterSCAN. “We’re detecting SARS-CoV-2 in 100 percent of our samples across the country right now.”

WastewaterSCAN also began monitoring in early 2022 and the number of sites that it monitors has changed over time.

“Despite these changes, it’s notable that levels right now for WastewaterSCAN are much higher than previous summer peaks and yet still below the average concentrations at the height of the winter peaks in 2023, 2022, and 2021,” said Dr. Alexandria Boehm, professor of civil and environmental engineering at Stanford University and program director for WastewaterSCAN.

Health officials no longer track the coronavirus as closely as they did during the public health emergency, and there are no longer reliable estimates of daily or weekly new infections in the US. Instead, the nation is largely relying on wastewater levels to follow numbers of new cases.

Wolfe says the amount of virus in wastewater doesn’t precisely correlate to numbers of infections. That’s because there are a host of things that can influence how much virus is in wastewater – including how much water is flowing through the sewage system when sampling takes place, as well as how much virus people may be shedding with a given variant. Despite these variables, she says sampling over time has shown there is a strong relationship between the number of people infected in a given area and the amount of virus in local wastewater.

“We can’t say exactly how many more cases that may be compared to previous years, because some of those changes might have happened in the virus in the areas that we’re measuring,” she said.

The rise in cases is being driven by waning immunity in the population and a trio of new variants that have drifted enough from their parent virus, JN.1, to escape the ability of our antibodies to quickly neutralize them.

Cases are also climbing just as children head back to classrooms in many parts of the US, giving the infection plenty of opportunity to spread.

It’s not clear when this surge will peak and start to taper off.