Delta variant of coronavirus increasing rapidly in Sonoma County

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Sonoma County public health officials said Wednesday genetic testing of selected COVID-19 samples has detected at least 115 cases of the highly transmissible delta variant, a big jump from the 68 infections reported less than two weeks ago.

The finding mirrors a national trend in which the delta has now become the dominant coronavirus strain, said Dr. Sundari Mase, the county’s health officer.

Medical experts in California and nationwide say the large majority of people getting infected by the highly infectious delta variant are unvaccinated.

For weeks, Mase, along with state and federal health officials, have said this variant is primarily responsible for the recent uptick in COVID-19 cases and hospitalizations, including in Sonoma County.

“The vast majority of our samples selected for genotyping from May onward have been the Delta variant,” Mase said, noting the Centers for Disease Control and Prevention reported this strain of the coronavirus accounts for 83% of infections across the country.

Of the 115 local delta cases, 48 were detected using the county’s new genetic sequencing equipment, which was used for the first time July 13. During that initial run, 28 of 31 COVID-19 patient samples were confirmed to be the delta strain.

Mase said not all local coronavirus samples are being genotyped. Rather, county public health staff prioritizes certain virus cases. They include cases found among vaccinated and unvaccinated individuals, hospitalized patients and large outbreaks like the recent one at Santa Rosa’s main homeless shelter, Samuel Jones L. Hall. At least 90 residents there have been infected by the coronavirus since July 2, city officials said this week.

Eventually, the county expects to do broader genetic testing of COVID-19 samples to get a better idea of how the variants are spreading, the health officer said.

Statewide, the number of coronavirus patients being treated in a hospital has more than doubled in a month. Infections have accelerated further in the last two weeks, according to a Los Angeles Times report.

From June 22 to July 6, the daily number of COVID-19 patients hospitalized in California increased from 978 to 1,228, a nearly 26% increase, according to state data. Over the last two weeks, the daily count increased by an additional 76%, reaching 2,164 as of Monday.

The surge in cases and hospitalizations led Los Angeles County officials last Thursday to reinstate a mandate for residents to wear masks indoors. The following day, Sonoma County joined six other Bay Area counties and the city of Berkeley in recommending indoor mask use.

On Wednesday, Lake County health officials similarly urged local residents to use masks indoors. Health officials there reported Lake County, as of Tuesday, has a coronavirus transmission rate of 17 new daily cases per 100,000 residents, the highest in the state and almost twice the state average.

As of Wednesday, Sonoma County’s daily transmission rate is 9.5 cases per 100,000 people. To put that level of COVID-19 spread into perspective, under the state’s four-stage reopening plan scrapped in mid-June, a rate of 10 cases per 100,000 residents was considered widespread transmission and would have triggered the most restrictive purple tier of the state’s plan.

With an aggressive vaccination campaign that began in December 2020, the county has gotten close to that 70% minimum threshold of fully vaccinated people commonly called herd immunity. That’s the point when scientists say the coronavirus has a hard time spreading in the community. As of Wednesday, 69% of residents at least age 12 were fully inoculated against COVID-19.

“We have to let people know there’s still a big risk, especially if you’re not vaccinated,” Mase said. “You’re much more at risk of COVID if you’re not vaccinated.”

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

For information about how to schedule a vaccine in Sonoma County, go here.

Track coronavirus cases in Sonoma County, across California, the United States and around the world, go here.

For more stories about the coronavirus, go here.

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