Sewage water may offer early warning signs of COVID-19 outbreaks

ATLANTA - Think of it as an COVID-19 early warning system that starts when you flush.

Microbiologist Amber Schmidtke says that viral RNA ends up in wastewater, as it makes its way to water treatment plants.

"So, when a person is infected with COVID-19, part of the removal of the virus from their body is that they will shed it in their fecal material, or their poop," Schmidtke says.

To track the SARS-CoV-2 virus in sewage water, the CDC launched the COVID-19 Wastewater Surveillance System, in 2020, as a way to detect potential outbreaks -- or wastewater "signals" -- before they become obvious.

In the past week, CDC Director Dr. Rochelle Walensky says New York City and New York State have experienced a small rise in COVID-19 cases and New England a rise in hospitalizations, that may be tied to the contagious BA.2 omicron subvariant is now driving at least 50% of new infections in the Northeast.

"In fact, over the past two weeks, we've seen increasing wastewater signals in New York City and parts of New England, where we're now seeing increase in cases and some increases in hospitalizations," Walensky says.

So, how does wastewater surveillance work?

Public health workers collect samples of untreated wastewater as it flows into treatment plants, and then measure viral levels in the water determine if infections in a specific area are increasing or decreasing.

"So, what happens is, we start to see an uptick in the wastewater surveillance, and that usually predates what's going on with cases by about two weeks," Schmidtke says.

Testing wastewater can also detect cases that might otherwise get missed, if those who are infected do not have symptoms or do not get tested.

It also gives a more current snapshot of what is happening in a community, she says.

"We can see that (change) very, very quickly," Schmidtke says. "But, we don't always see cases in real time, because it does take some time between when a person is infected, and when they feel sick, and when they feel sick enough to seek out a test."

The CDC cautions wastewater viral levels remain low overall, which is why Schmidtke says it is important to track changes over time.

"There can be noise in the data," she says. "So what I mean to say is we're not going to panic, if we see a big day, but we are going to panic, or not panic, but get concerned, if we see 3 or 4 or 5 days worth of a steady increases. That could be a warning sign."

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