Staff Photo by Matt Hamilton / Hamilton County Mayor Jim Coppinger speaks during a news conference Thursday at the Hamilton County Health Department.

A change to the way COVID-19 data is collected and reported could affect local groups relying on active case counts to determine their reopening plans.

The Tennessee Department of Health announced last week that it would be changing its COVID-19 reporting guidelines on active cases. The state considers someone an active case for 14 days after the start of illness or, for asymptomatic infections, when a test was conducted. The previous time frame was 21 days for recovery.

The change follows guidance by the U.S. Centers for Disease Control and Prevention, which says most people infected with COVID-19 are not at risk of spreading the virus after that time period despite fragments of the virus possibly still being present in their bodies.

Rae Bond, chair of the local COVID-19 Joint Task Force, said during a weekly news briefing that health experts are constantly learning more about COVID-19 and updating best practices.

"It's the 'novel' coronavirus because we hadn't experienced it before," Bond said. "So, as epidemiologists and health researchers learn more about the virus, some of the guidelines will change over time. They now know a great deal more about how the virus is transmitted, so that's why the guidelines have been changed and how long the contagion period is."

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Dropping a week from the reporting guidance caused a significant drop in the number of reported active cases in Hamilton County. On Sept. 3, the health department reported 1,701 active cases. On Sept. 4, the first day of the new rule, the department reported 901 active cases. On Tuesday, there were 983 active cases in the county.

"The change in calculating active cases is to make the active cases count more accurate for groups using this information for decisions," said Becky Barnes, Hamilton County Health Department administrator.

Groups such as Hamilton County Schools follow active case counts in their reopening plans. The school district announced Aug. 24 that it would enter Phase 3 of its plan, which includes five days per week of on-campus learning.

Last week, the number of active cases had the district hovering between the current Phase 3 and Phase 2, a stricter measure that reduces days of on-campus learning. The change in reporting active cases moves the district clearly into Phase 3.

Tim Hensley, district communications director, said Tuesday morning he was not aware of any changes to the district's reopening plan due to the data change.

(READ MORE: Hamilton County parents, teachers find their way through education disrupted by COVID-19 pandemic)

Barnes said the health department is also aware of a data discrepancy in the number of cases reported by the state versus what is reported locally. In the early months of the pandemic, the state's total case count for Hamilton County was often lower than what the county reported. County officials said at the time the difference was because of a delay in reporting test results to the state.

However, on Aug. 16, the county total reported by the state became higher than what was being reported locally. On Friday, the state reported 8,594 total cases in Hamilton County and 714 active cases, compared to the 8,479 total cases and 983 active cases reported locally.

Contact Wyatt Massey at or 423-757-6249. Follow him on Twitter @news4mass.