COVID demographics in sonoma county march 27

New system aligns with state, allows for better understanding of new tier system

In order to align more directly with the state, the Sonoma County Department of Health Services has changed the methodology it uses to tabulate the number of COVID-19 tests conducted, as well as the county’s testing positivity rate. Starting Sept. 14, these changes will result in the posting of new data on the county’s COVID-19 dashboard.

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 because, under Gov. Gavin Newsom’s new “Blueprint for a Safer Economy” for reducing COVID-19, they determine how soon counties will be able to move from one tier to the next. The blueprint replaces the old county watchlist, and is a color-and-number-coded chart of four tiers — Purple/Tier 1 for widespread, Red/Tier 2 for substantial, Orange/Tier 3 for moderate and Yellow/Tier 4 for minimal. Each tier has a metric a county must meet for daily case rate per 100,000 (a seven day average with a seven day lag) and testing positivity rate (a seven day average with a seven day lag).

Sonoma County is currently (as of the most recent data collection on Sept. 10) in the most-restrictive risk group of Purple/Tier 1. Under the new system, the county’s seven-day average case rate per 100,000 residents stands at 11.2, while its seven-day average positivity rate is 5.3%. To drop down to the red tier, it would have to see its average daily virus case rate per 100,000 residents drop below seven. The county also would need to see its overall percentage of positive tests drop below 8%.

If a county’s case rate and positivity rate fall into different tiers, the county remains in the stricter tier. This is the case for Sonoma County, as its new case rate is well over the metric, but its testing positivity rate is below.

Counties in the Purple/Tier 1 group were allowed to open some businesses and activities with modifications, including all retail, shopping centers at maximum 25% capacity, and hair salons and barbershops indoors. Schools in the tier aren’t permitted to reopen for in-person instruction, unless they receive a waiver from their local health department for TK-6 grades.

Schools can reopen for in-person instruction once their county has been in the Red/Tier 2 group for at least two weeks. Schools must follow specific guidelines when they reopen or if they have to close again.

“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 Sonoma County Health Officer Dr. Sundari Mase. “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. 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 also 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 Health (CDPH). County health officials have been working closely with the state to understand why the numbers differ. 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 an individual took multiple tests. This did not impact the county’s ability to identify or conduct contact tracing with individuals. It did, however, underestimate the number of tests performed per day.

With the inclusion of this information, Sonoma County's metrics will now more closely align with CDPH reporting.

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