Virus cases dip markedly since summer surge
The spread of coronavirus has slowed significantly since the peak of the Bay Area’s summer surge, with new cases falling over 60% since the difficult days of midAugust.
Specifically, the region’s nine Bay Area counties reported an average of 513 new cases per day in the week ending Sunday, down 35% from an average of 788 per day in the week ending the previous Sunday. The last time the Bay Area reported fewer than 500 cases a day, on average, was in June, around the time the summer surge began to accelerate.
If you compare last week’s numbers to the midAugust peak of 1,409 cases per week, that’s a 64% decline, according to data collected by The Chronicle.
The decline in coronavirus cases may come as a welcome surprise to Bay Area residents, who have been focused on wildfire destruction and smoky skies over the past two weeks. It is most likely because people are consistently wearing masks and social distancing, experts said. In other words, changes in human behavior over time are finally reaping some progress on the public health front — though they are taking a grave economic toll.
“People have to incorporate these practices in their routine activity; I think that’s particularly true in the Bay Area,” said Dr. Lee Riley, head of the division of infectious diseases and vaccinology at the UC Berkeley School of Public Health. “Most people are wearing masks and maintaining the 6 feet distancing recommendations. And the businesses are still restricted from operating. So I think these prolonged measures are having an impact.”
It remains to be seen whether case counts will continue to sink as state and county officials work to slowly reopen the economy while avoiding another surge.
The number of Bay Area residents hospitalized for the coronavirus has been in a similarly gradual decline since late July, according to state data. Bay Area hospitalizations peaked at 781 during the week ending Aug. 2, and have declined relatively steadily each week since. They fell to 508 in the week ending Sunday, a 35% decline from the peak.
Marin County is seeing the lowest threeday hospitalization rates since midJune, and Contra Costa County last week reached its lowest hospitalization levels (62 patients) since the first week of July, health officials for the counties said Tuesday. But in San Francisco, hospitalizations have been rising since early September, from 51 on Sept. 4 to 76 on Sept. 13, according to city data.
So far, the wildfires that began in August have not appeared to lead to an overall, regional uptick in transmission. Health officials had feared that scenario, worrying that as evacuees gathered in shelters, they might mix households and spur the spread of the virus.
But evacuees were mostly sent to hotels rather than staying in a single, large evacuation center, which helped prevent the spread from worsening in shelters, said Solano County Health Officer Dr. Bela Matyas.
The August heat wave, coupled with poor air quality from the fires, may also have helped slow down the spread by discouraging people from meeting up with friends outdoors.
“Bad air, especially with heat, greatly diminished people’s impetus to do socializing,” Matyas said. “There was a lot more staying indoors than would’ve occurred during that period otherwise. That has helped contribute to a reduction in transmission.”
However, the current spate of wildfires in Northern California, the recent passage of Labor Day and the upcoming winter holidays have some health experts worried anew. The summer surge was partly attributed to large gatherings among friends and family members over Memorial Day and Fourth of July holiday weekends. People may again be tempted to let down their guard and relax social distancing and maskwearing in these settings.
“Our numbers are good but I’m worried that Labor Day is going to bump us back up,” Matyas said. “We have to wait it out . ... Typically it’s two weeks you have to wait. We’re one week in from Labor Day weekend. This week will be telling whether our numbers are bumped up by it.”
A turn to cooler weather poses another risk.
“The biggest concern is once the weather turns and it gets colder, there will be a lot more indoor gatherings of people,” said Dr. George Lemp, a retired University of California epidemiologist. “In November and beyond, once the holiday season comes, people are going to want to gather and because of the weather turning, it’ll be more likely indoors.”
There are other signs the virus is slowing down in the Bay Area. The metric commonly known as “Rnaught,” which measures the number of people that each infected person spreads the virus to, is stable or decreasing in all nine Bay Area counties, according to state data. The Rnaught needs to be below one in order for the spread to slow. In all but one Bay Area county, it is. Most counties range between 0.8 and 0.9, while San Mateo measures in at exactly one.
However, the number of coronavirusrelated deaths in the Bay Area is not declining. It has hovered between about nine and 12 people a day, on average, for the last several weeks. Experts say that is not unexpected, given the relatively low number of deaths here compared to harderhit regions. And there is less of a clearcut correlation between cases and deaths than, say, cases and hospitalizations. Deaths are relatively uncommon and can occur anytime — from just a day or two after a diagnosis, up to weeks or even months later.