Bay Area’s contact tracers struggle amid coronavirus surge

Contact tracing — finding and notifying everyone who has had close contact with a person infected with the coronavirus — is key to stemming the pandemic. Once people learn they’ve spent time near someone who had the virus, they can get tested themselves and quarantine so they don’t infect others.

Bay Area county health departments ramped up in April and May to handle the laborious process, most of it armchair detective work by phone and email, not the high-tech surveillance some in Silicon Valley originally envisioned. But the recent surge in cases has made the task much harder, because there are more people to contact and because it takes longer to be tested and then get the results.

Alameda, Contra Costa, Marin, San Francisco, San Mateo and Santa Clara counties all fall short of their goal of doing case investigations for 90% of the people who test positive, and then reaching out to 90% of the folks those people had close contact with while they were infectious.

Napa, Sonoma and  Solano  counties did not respond to requests for information.

When it comes to reaching contacts of the people who tested positive, the counties range from 70% to 80%, except for Contra Costa, which reaches only 26% of those who had contact with infected people, and Marin, which reached only 46% (its numbers are older). Still, those numbers are far better than those in New York and some other states.

“Obviously we want as many as possible because that’s where you get the most bang for your buck,” said Dr. George Rutherford, an infectious diseases expert at UCSF who spearheaded San Francisco’s contact-tracing program. But modeling shows that even reaching 43% of infected people’s contacts provides some disease suppression. “I think the spread would be worse without” contact tracing, even though it hasn’t reached its potential, he said.

Contra Costa County could not say why it is so far below the Bay Area norm, especially since it is closer than Alameda and San Mateo counties to meeting its contact tracing staff goal.

“We’ve been grappling with it,” said Erika Jenssen, deputy director of Contra Costa Health Services. “To do effective contact tracing, we need timely lab results for tests, adequate staffing and to partner with the community.”

She pointed to delayed test results as a major obstacle. While the median turnaround time in the county is four days, many results come in as late as 10 days after testing — by which time a person may not longer be infectious.

And it’s not just results that take a while: In parts of the Bay Area, some people must wait a week or more for a testing slot to open up.

The case investigations — interviews with newly diagnosed people — shed light on how the virus has spread since shelter-in-place orders were eased.

“We are seeing more people who were at some kind of gathering; that’s a common source of exposure,” Jenssen said. Contra Costa County investigators found that 18% of those who tested positive had attended large gatherings in the previous 15 days, while 17% had been to in-person workplaces. About 20% had visited restaurants, supermarkets and other stores.

Even counties that have maintained fairly high contact tracing numbers say they struggle with the surge.