Last week, confirmed COVID-19 cases in children ages 6-19 years old in St. Louis County saw a historic spike.

Forty-nine new cases of COVID-19 were found in this age group during the week of Aug. 2-8, making it the county's biggest increase in any age group during any week since the pandemic's start. Over half of these new cases were identified in a narrow demographic of this group: 18- and 19-year-olds.

Amy Westbrook, public health division director for the county, said it's difficult to pinpoint exactly why cases in the younger age group rose last week.

Over 60% of the county's total cases occurred last month, so it "makes sense" that COVID-19 cases increased. But, Westbrook said, it's concerning when a large number of them were found in a specific age cohort.

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The county is most concerned about 18- and 19-year-olds, as they made up around 56% of the new cases found in those between 6-19 years old. The county groups teens with children as it follows state age groupings.

"They do act more like adults, in terms of transmission," Westbrook said, because they belong to the workforce and attend social gatherings. She encourages them to be cautious and follow safety guidelines.

"Everybody across the age spectrum has a role and a responsibility for prevention and control for their own individual health (and) to protect other's health," she said.

Statewide, around 12% of the total cases can be found in the 6- to 19-year-old age cohort. In St. Louis County, that figure is slightly higher, with approximately 16% of the county's total 600 cases located in the younger age group, according to the county's COVID-19 dashboard.

Younger, healthy people can more easily fight off COVID-19 and avoid hospitalization. And some studies have shown that people younger than 10 are less likely to spread the virus or get infected, Westbrook said.

"Kids older than 10 seem to act more like adults, in terms of transmission and spread," she said.

However, this younger age group is likely to be living with older people, whether it's their parents, guardians and/or grandparents — people who are more likely to suffer from adverse symptoms.

Although the county hasn't determined if the virus has spread through multi-generational households, Westbrook said it's possible that younger people could transmit the virus to older members of their households.

"If there are multi-generational households, some of those people in that household could be at a higher risk of morbidity and more severe illness," she said.

Westbrook pointed out that although a large percentage of the county's cases are located within the 6-19 and 20-29 age groups, the median age of people who are hospitalized or die are decades older.

As of Wednesday, the median age for people who are hospitalized due to the virus is 73 years old, while the median age of people who die from the virus is 84 years old.

The new cases in children and teens come on the heels of a new national report that found cases in U.S. children soared in late July, with the number of cases increasing by 40%.

And with school restarting in a few weeks and school districts in the midst of reopening decisions, Westbrook called the timing of the new cases "unfortunate."

"It's unfortunate that we're seeing this increase when schools are ... making these decisions for our young people," she said.