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Coronavirus material found in Twin Cities wastewater declined 1% over the past week, matching the gradual statewide decline in COVID-19 cases this summer in Minnesota.

Friday's update from the Metropolitan Wastewater Treatment Plant in St. Paul showed that a BA.5 variant — responsible for COVID-19 growth in southern and western states this summer — made up 64% of the viral material in sewage samples. The amount of BA.5 in Twin Cities wastewater was unchanged over the past week.

Sewage sampling has become a vital monitor of the COVID-19 pandemic, because shifts in diagnostic testing have artificially reduced the number of infections that are identified. People have shifted from COVID-19 testing at clinics and testing centers to at-home tests that aren't reported publicly.

"We know that we are not catching the same proportion of cases that we did earlier in the pandemic," said Stephanie Meyer, supervisor of the Minnesota Department of Health's COVID epidemiology unit. "This has us closely watching for community impacts, especially on our hospitals and health care systems. Though those figures are not as low as we would like, they are holding steady for now."

COVID-19 hospitalizations in Minnesota have hovered around 400 for the past two months — reaching 407 on Wednesday. BA.5 and other omicron subvariants of the coronavirus have caused lower rates of illness this year, but spread quickly even among people with immunity from recent vaccinations or infections.

Wastewater results have been up and down over the past month, leaving health officials uncertain whether BA.5 will fuel a new COVID-19 wave in Minnesota like it is doing in Florida, California and other warm-weather states. Mayo Clinic's 14 day pandemic model predicted a rise in COVID-19 cases after the Independence Day weekend but now forecasts little change in infection numbers through the end of July.

The fact that both wastewater and case numbers are trending downward is a good short-term sign for Minnesota, although the Centers for Disease Control and Prevention on Thursday found that three counties in the state had high COVID-19 levels and 22 counties had moderate levels. The CDC had only found three counties the prior week with moderate COVID-19 levels, a composite measure based on local case and hospitalizations numbers.

The Ensemble model, aggregating predictions from multiple U.S. institutions, predicts no change in COVID-19 hospital admissions in Minnesota for the next week.