Where are Coronavirus 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.

In other Southern California counties, it’s less clear what’s driving the higher infections. In the last 14 days, Imperial has had nearly 14 cases, Los Angeles nearly 12 cases, Riverside more than 6 cases, and San Diego nearly six cases per 10,000 people.

By contrast, Santa Clara, the most populous in the Bay Area county and an early U.S. hot spot in the pandemic, has just over 1 case per 10,000 people in the last 14 days, while Contra Costa County has had nearly 2, Alameda almost 4, San Mateo more than 5 and San Francisco, which has tested aggressively for the disease, nearly 6.

The regional disparity is also showing up in hospitalizations.

Statewide, the number of current confirmed and suspected COVID-19 hospitalizations has steadily plateaued over the last month to just over 4,500. In the 10 greater Bay Area counties, the daily trend line this month has declined from 550 to about 500, but in the 10 southernmost counties, it has held flat around 3,700, a Bay Area News Group analysis found.

The differences are even more stark by comparing Santa Clara County, which has been slow to loosen shelter-in-place restrictions, and Orange County, where local officials have clashed with Gov. Newsom over the opening of beaches.

Since April 13, Santa Clara County’s hospital count fell from 217 to 84 on Tuesday — a 61% drop. Orange County, meanwhile, saw the number of hospitalized COVID-19 patients during the same period rise from 230 to 348 — a 51% jump.

The Bay Area was the first in the country to enact shelter-in-place orders in mid-March to slow the virus’ spread. Southern California counties for the most part followed the statewide stay-home order that came a few days later.

But Noymer and other health experts aren’t sure that would still affect new cases occurring in recent weeks.

“A couple days can make a difference at the beginning of an epidemic,” said Dr. Lee Riley, professor of epidemiology and infectious diseases at UC Berkeley. “But at this time, we should be seeing a similar rate of infection.”

Other factors also could play a role in the different experience in the northern and southern parts of the state.

The disease spreads most easily through close contact, so people who live in high-density apartments and condominiums or with many family members packed into a house will be more vulnerable if one member of the household becomes ill. The five most populous counties in the state are in Southern California: Los Angeles, San Diego, Orange, Riverside and San Bernardino. That could also help explain the recent high infection rate in densely packed San Francisco.

An increase in testing also can influence the results. Of the 10 counties with daily testing rates of at least 1 per 1,000 people, four also are among the 10 with the highest infection rates: Imperial (3.8), Mariposa (2.8), San Francisco (1.7) and Los Angeles (1.3). Santa Clara is testing 0.5 and Contra Costa 0.4 per 1,000. Alameda County hasn’t reported testing rates.

Riley speculated that other factors, like the prevalence of high-tech companies that make working from home easier, could be lowering infection rates in the Bay Area. But he said without data about how people are getting sick under the lockdown, it’s difficult to target an effective response.

“If the lockdowns are working,” he said, “we should not be seeing new cases.”

 

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