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Transmission of the COVID-19 virus in bars, food plants and other locations has resulted in an erratic spread of the pandemic in Minnesota, where the addition on Thursday of 365 lab-confirmed cases brought the total so far to 34,123.

The Minnesota Department of Health on Thursday also reported nine deaths, for a total of 1,406 in the pandemic. The state also reported that 336 patients are hospitalized with COVID-19, a respiratory disease caused by a novel coronavirus, and that 162 required intensive care.

Minnesota's case count only includes those confirmed through diagnostic testing, though. A top federal health official on Thursday said it is likely that as many as 5% to 8% of Americans have already been infected — given the number of cases that involved mild or no symptoms.

If true, that means that as many as 450,000 Minnesotans have already been infected.

The U.S. Centers for Disease Control and Prevention also has been collecting serology test results from blood banks and researchers across the country to find out how many people already have antibodies suggesting that they have been infected. And the results suggest an even broader spread of the virus.

"Our best estimate right now is that for every case that was reported there actually were 10 other infections," said Dr. Robert Redfield, CDC director, in a media briefing Thursday morning.

Case growth since the start of June has been erratic across Minnesota, with the city of Marshall and surrounding Lyon County in the southwestern part of the state seeing its numbers increase fivefold from 57 on June 1 to 284 on Thursday.

Numbers in Mower County in southern Minnesota have more than doubled from 345 to 847, largely due to an outbreak in a food processing plant. Cases in Blue Earth County nearly doubled as well from 142 to 281, partly due to the spread of the virus among people revisiting reopened bars in mid-June, state health officials said.

Case growth has ebbed elsewhere. Stearns County in central Minnesota had been a hot spot due partly to outbreaks in food-processing plants, but cases have only increased 5% — from 2,030 to 2,141 — since the start of the month.

The deaths reported in Minnesota Thursday included 5 residents from long-term care or assisted-living facilities who have been at increased risk of severe COVID-19 due to their ages or underlying health conditions such as diabetes, asthma and diseases of the lungs, kidneys and heart. Deaths from COVID-19 so far in the state include 1,107 residents of these facilities.

The median age of all known COVID-19 cases in Minnesota is 39.7, and of deaths is 83.6.

Nationally, an increase in cases has been fueled by more young people suffering infections and undergoing diagnostic testing, CDC officials said.

Redfield said this remains a serious situation, with young people spreading the virus to others at greater risk. However, he said the nation isn't in the same "shocking" situation as it was in the spring when 27% of all deaths in the U.S. were due to COVID-19, pneumonia or influenza.

"We're in a different situation today," he said, "than we were in March and April."

Jeremy Olson • 612-673-7744