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Wastewater tests show an uptick in COVID virus. But reported cases don’t match

A stock image of wastewater testing.
Felipe Caparrós
Adobe Stock
A stock image of wastewater testing.

Local wastewater samples are showing an increase in the virus that causes COVID-19.

Experts said the upward trajectory, a pattern that has unfolded over the last two weeks, is similar to when the omicron BA.5 subvariant caused a surge in cases a few months ago.

“Remember in April, we were very worried, we were all wearing masks? Well, the wastewater says we're pretty close to where we were in April,” said Katrina Korfmacher, UR Medicine’s environmental health specialist.

During the first two years of the COVID-19 pandemic, counties across New York began testing wastewater to discover which communities were most affected by the virus. In April, when tests of wastewater showed rising levels of COVID-19 RNA in Monroe County, the trend was accompanied by a rise in reported infections.

Korfmacher said this time around, the reported infections do not match the trend.

In April, the county reported more than 600 positive cases per week. As of Monday, the reported seven-day average was 133 cases.

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“That relationship between what the wastewater is telling us and what people are experiencing is different,” Korfmacher said.

Dr. Edward Walsh, an infectious disease specialist at the University of Rochester Medical Center, said this is a result of more people becoming immune and experiencing milder symptoms. That, he said, may result in them doing one of two things: not testing at all and just chalking it up to a cold, or test themselves at home.

“We know that a good proportion of those positive (at-home) tests are not being reported to the health department,” Walsh said.

That may explain the current discrepancy between the wastewater test results and the number of reported COVID cases.

“Everybody poops, so when you test the concentration of that virus's RNA in the wastewater, it doesn't lie,” Korfmacher said.

Another possible factor: A new study from researchers at Cedars-Sinai Medical Center, published in JAMA Network Open, found more than half of people infected with omicron are never aware they're sick.

Walsh said the decline in reported cases can also be looked as a positive thing. He said it’s an indication that the virus is not causing severe disease or increased hospitalizations.

“Whether you want to call it herd immunity, or just general immunity for COVID, it's clearly much greater today than it ever has been,” Walsh said.

Racquel Stephen is WXXI's health, equity and community reporter and producer. She holds a bachelor's degree in English literature from the University of Rochester and a master's degree in broadcasting and digital journalism from the S.I. Newhouse School of Public Communications at Syracuse University.