San Diego County reports single-day coronavirus case record

At Birch Aquarium at Scripps Institution of Oceanography on Thursday, children reach into shallow tanks to pet sea creatures.
At Birch Aquarium at Scripps Institution of Oceanography on Thursday, children reach into the shallow tanks to pet various sea creatures at the Tide Pools exhibits. Beginning Saturday, all indoor exhibits will be closed due to new COVID-19 restrictions with only outdoor exhibits and activities being open.
(Nelvin C. Cepeda / The San Diego Union-Tribune)

New map shows tier levels down to the ZIP code level


As COVID-19 continued to threaten nationwide hospital capacity, San Diego County reported a single-day coronavirus case record Thursday.

The record actually occurred on Tuesday when the county health department was notified of 661 new positive cases, though nobody heard the news until Thursday because there was no county COVID-19 report Wednesday in observance of Veterans Day.

But a day late did not change the math. Tuesday’s total bested the previous single-day record of 652 set on Aug. 7. Though not a record, Wednesday’s total of 620 none-the-less underlined what appears to be a new reality: local coronavirus transmission has spiked since Halloween.

So far, though, elevated numbers of cases recorded throughout the region have not yet translated to overwhelmed hospitals. A survey of local health systems Thursday found none reporting a hospitalization surge large enough to force transfers to other facilities as was the case during the last big spike in the summer.

The higher totals came as San Diego County prepares for the plunge to the most-restrictive purple level of the state’s COVID-19 reopening system. In the lowest tier, restaurants, places of worship, movie theaters and other locations will no longer be allowed to operate indoors.

While some organizations, such as the Birch Aquarium at Scripps worked to set up exhibits outdoors Thursday, others appeared to stand firm on previous statements that they simply will not go along with the state’s forced outdoor migration.

The color-coded system that has caused so much concern and consternation in San Diego County took on a new level of detail Thursday with the release of a new map that shows, by ZIP code and individual city or unincorporated jurisdiction, the specific tier based on each area’s number of cases per 100,000 residents.

Map of case rates by ZIP code

Dr. Wilma Wooten, the county’s health officer, announced the maps during a news conference Tuesday, indicating that it will be updated every Thursday by using the same seven-day period that the state uses to make tier assignments every Tuesday for every county in the state. This week’s map looks at cases with illness onset dates that fell into the seven-day window from Oct. 25 through Oct. 31.

From Alpine to Spring Valley, it is now easy for residents to see the tier level of the place they live based on the number of cases per 100,000 residents over a seven-day period lagged seven days from the present.

It’s quite a picture to behold, with purple swallowing up most places but also with pockets of red in Santee, La Mesa, Encinitas and Carlsbad and a few spots of orange in Del Mar and Poway, highlighting areas where the local population appears to be doing somewhat better and keeping transmission lower-than-average.

However, as is the case with any picture painted with pure statistics, this map is not perfect.

It assigns clear colors to small places such as Rancho Santa Fe, Del Mar, Julian, Valley Center, Jamul and Borrego Springs. But anyone who has ever taken an introductory statistics class understands that, as the numbers get smaller, it just does not take much to end up at the extreme ends of the scale.

Rancho Santa Fe is probably the best example.

Most might expect this well-off unincorporated area north of Del Mar to lead the region in terms of low coronavirus case rates. After all, the Ranch, as it’s often called, features large lots — the kind of social distance few can afford.

And yet, on the county’s map, Rancho Santa Fe is just as purple as the South Bay areas that saw widely-reported COVID-19 surges this summer.

How many cases did it take to turn the Ranch purple? Just 7 were enough to give the region, home to only 3,117 people, a case rate of 32 per 100,000. That’s 4.5 times higher than the state’s limit of no more than 7 to remain in the red tier.

Statistically speaking, small sample sizes can deliver wild swings.

The map better tracks reality in places with larger populations.

Overall, only one local city with more than 100,000 residents managed to keep itself from turning purple on the county’s map. With 41 cases in the seven-day window among 115,241 residents, Carlsbad remains in the red with a local case rate of 5.1.

— Paul Sisson is a reporter for The San Diego Union-Tribune