Where are cases surging in California — and why?

As California looks to ease stay-home restrictions imposed to keep COVID-19 in check, infections of the new coronavirus seem to be spreading fastest in the southern third of the state, according to a Bay Area News Group analysis.

Of California’s 58 counties, eight of the 10 with the highest rate of new infections are in Southern California. The infection rate is a key metric Gov. Gavin Newsom’s administration is reviewing to allow counties to ease restrictions — to demonstrate “epidemiologic stability,” they must have no deaths and no more than one new infection per 10,000 people in the last 14 days.

The 10 counties with the highest rate of infections per 10,000 people over the last 14 days are Santa Barbara,

Kings, Tulare, Imperial, Los Angeles, Mariposa, Riverside, San Francisco, San Bernardino and San Diego. Of those, only San Francisco and Mariposa are in Northern California.

Public health experts aren’t sure why Southern California counties seem to be having a harder time corralling the new coronavirus lately.

“It’s a mystery to me,” said Andrew Noymer, associate professor of population health and disease prevention at the University of California-Irvine. “It just doesn’t totally make sense.”

But there are some explanations.

In some Southern California counties, recent isolated clusters of new cases have driven high infection rates. In Santa Barbara County, with nearly 20 new cases per 10,000 people in the last two weeks, health officials told news reporters this week that two-thirds of the cases involved a rash of infections among inmates at two federal prisons in Lompoc.

Likewise, in rural Kings County, with nearly 16 new cases per 10,000 in the last two weeks, Supervisor Doug Verboon told the Fresno Bee that nearly two-thirds of its cases in the first week of May were connected to an outbreak among workers at the Central Valley Meat Co. packing plant in Hanford.

In Tulare County, with almost 14 cases per 10,000 in the last two weeks, infections have surged with outbreaks tied to nursing homes and food processing plants such as Ruiz Foods, but there also has been significant “community spread,” according to local news reports. San Bernardino, with almost 6 cases per 10,000 in the last two weeks, has seen a number of outbreaks at elder care homes and state prisons.