Sonoma County revamps calculation of key data tracking coronavirus outbreak

Sonoma County public health officials have changed how they calculate the two key benchmarks the state uses to track counties’ progress in managing the coronavirus pandemic.

The county is making the calculation changes in order to match the state’s methodology for determining the overall share of positive virus tests and the number of new COVID-19 cases per 100,000 residents.

The move, announced Monday, positions the county to possibly be able to ease business restrictions sooner on higher-risk operations such as indoor restaurant service, fitness centers and movie theaters, under Gov. Gavin Newsom’s new four-stage reopening plan.

During a press briefing, county Health Officer Dr. Sundari Mase said the methodology change is meant to reconcile discrepancies between the county and state’s differing COVID-19 new case and positivity rates.

Although both rates will improve under the new methodology, the county’s case rate per 100,000 people — a reflection of virus transmission — still falls short of the state minimum for local public health officials to be able to immediately lift business restrictions.

Under the state’s new reopening plan implemented last month, California’s 58 counties are assigned to four separate tiers representing the level of virus spread: widespread; substantial; moderate; and minimal. Sonoma County remains in the widespread stage with the most limitations on business activities.

Under the new methodology, the county’s 7-day average new case rate per 100,000 residents is 11.2, while its 7-day average virus positivity rate is 5.3%. With the old methodology, the county’s case rate stood at 13 new infections per 100,000 people and a positivity rate was more than double at 11.5%.

To advance to the next reopening stage deemed substantial virus spread, Sonoma County has to further reduce its daily rate of new cases per 100,000 people to between 4 and 7, while keeping the overall virus test positivity rate between 5% and 8%. Before advancing, the county has to attain both state benchmarks and hold those levels for at least two weeks.

Progressing to the next reopening stage would enable the county to resume indoor dining and drinking at restaurants, wineries and breweries with limits. Those establishments could restart business inside at 25% capacity or no more than serving 100 people at once, whichever is fewer.

Also, movie theaters and museums could reopen indoors at 25% capacity. Gyms and fitness studios could resume indoor activities at 10% capacity, while retailers could expand operations from 25% to 50% capacity.

Kathryn Pack, health program manager for the county’s epidemiology team, said county public health staff have been working with state officials to resolve differences between local and state virus data.

Last week, county health officials received and reviewed the state’s “analysis code” for processing virus testing data and determined that local calculations were unintentionally underestimating the number of tests being done in the county. Pack said the county’s analysis of COVID-19 test data was not counting multiple tests conducted on the same individual.

“The implication of this is that we are testing more than we thought we were testing,” Pack said. “And when you have more tests, that also as a consequence will lower the overall testing positivity.”

Paul Gullixson, a county spokesman, called the methodology change the county made a “numbers” issue that had no effect on the local pandemic response or the county’s pace of reopening businesses under state guidelines because that has “always been determined by the state numbers.”

You can reach Staff Writer Martin Espinoza at 707-521-5213 or martin.espinoza@pressdemocrat.com. On Twitter @pressreno.