'Breakthrough' Leads To Change In Sonoma County Coronavirus Data

SONOMA COUNTY, CA — Changes to the way the Sonoma County Department of Health Services tracks the number of coronavirus tests conducted and the rate of positive tests in the county are expected to align the county's numbers with the state's.

"Once implemented, these changes will result in the posting of new data on the County’s COVID-19 dashboard," county officials said Monday in a news release. "The new methodology, which will be applied retroactively, will show an overall increase in testing volume as well an associated decrease in Sonoma County’s testing positivity rate."

The consistency of these two metrics is vital, the county said, because under California Gov. Gavin Newsom’s new "Blueprint for a Safer Economy" for reducing COVID-19, the metrics determine when a county can move from one tier to the next.

Sonoma County is currently in the most-restrictive purple tier, meaning its average daily virus case rate per 100,000 residents needs to drop below 7 and its overall percentage of positive tests needs to drop below 8 percent.

Under the county’s previous methodology, the numbers, as of last week, stood at 13 cases and 11.5 percent respectively.

Under the county’s new data, which more closely aligns with numbers from the California Department of Public Health, the county’s seven-day average case rate per 100,000 residents was 11.2 while its seven-day average positivity rate was 5.3 percent.

"This change should clear up the confusion about discrepancies about the State’s numbers and the County’s numbers, leaving us in a better place moving forward," said Dr. Sundari Mase, Sonoma County's health officer.

"But it’s important to note that these updates would not have resulted in any change to the COVID-19 policy decisions made previously regarding our County," Mase said. "It’s the State’s numbers, not the local ones, that determined whether Sonoma County was on the watchlist and, later, where we would be grouped under the governor’s new four-tier plan."

Mase noted that multiple measures have factored into local decision-making and that no single metric guides policy. In addition to testing positivity, for instance, health officials monitor trends in case rate, critical care capacity, and the occurrence of outbreaks and deaths due to COVID-19.

As with many counties throughout California, Sonoma County's local COVID-19 statistics have varied from those reported by the California Department of Public Health, said Sonoma County Spokesman Paul Gullixson.

"County health officials have been working closely with the State to understand why the numbers differ," Gullixson said. "A breakthrough came when state officials recently provided Sonoma County with analysis code not previously made available to local health jurisdictions."

Through this new guidance, it was discovered that prior file-cleaning protocols were unintentionally undercounting instances where one person took multiple tests, Gullixson said.

This did not impact the county's ability to identify or conduct contact tracing, but it did underestimate the number of tests performed per day.

With the inclusion of this information, Sonoma County expects its metrics to more closely align with California Department of Public Health reporting.

The public can track Sonoma County’s progress in slowing the spread of the COVID-19 virus by going to SoCoemergency.org.

According to the web page, as of 8:30 p.m. Monday, the total number ofcoronavirus cases in Sonoma County since March was 6,738 (1.32 percent of the county's population); the number of active cases was 1,747 (0.34 percent of the population); the number of people who've recovered from the virus was 4,881 (72.44 percent of cases); and the number of deaths was 110 (1.63 percent of cases).