With a new wave of coronavirus cases rampaging across the country, the Centers for Disease Control and Prevention this week urged local health officials to prioritize the use of contact tracing to new cases that could likely interrupt further spread of COVID-19. But the Bay Area’s hardest-hit counties say they aren’t planning to triage just yet.

The CDC guidance recommends health departments slammed with a surge in cases focus contact tracers on those diagnosed in the past six days, on members of their household and those living, working, or visiting congregate living facilities, high-density workplaces or other settings with potential for explosive spread.

The revision acknowledges that the strategy of health officials interviewing patients to learn whom they may have exposed and then asking those people to quarantine and reveal whom they might have exposed, has struggled to keep up with successive waves of COVID-19 cases in the U.S.

In the Bay Area, however, health officials in some of the largest counties said that despite surging case loads, they haven’t yet reached a point where they need to scale back contact tracing.

“We’ve already been planning for an influx of cases,” said Will Harper, spokesman for the Contra Costa County public health department, which is reviewing the CDC guidance and plans to discuss it next week. “Even with a large influx of cases, our expectation is that we reach out to all cases within 24 hours of them being entered into the state’s CalConnect system,” which tallies coronavirus data.

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In Santa Clara County, Assistant Health Officer Dr. Sarah Rudman, said that “if our ability to keep up changes, we are prepared to triage as recommended by the CDC and have already trained staff to do so.”

“Fortunately, with existing resources and minor changes to our procedure, we have been able to keep up with the current surge of cases and continue to be able to attempt to reach all cases and contacts,” Rudman said. “But we focus on reaching the most recent cases first.”

Alameda County is bringing on additional staff to respond to the current case surge, said spokeswoman Neetu Balram.

While contact tracing was seen as a key tool to tamp down outbreaks and was key to reopening plans from New York to California in the spring, it has had limited effectiveness across the country for a variety of reasons.

“The tool of contact tracing is really effective when we have a low level of cases in our communities,” said Crystal R. Watson, a senior scholar at Johns Hopkins University’s Center for Health Security. “Because it’s really resource intensive, you can’t expand exponentially the number of people working on contact tracing.”

She said that across the country there are only about half the 100,000 contact tracers that health experts believed would be needed back in the spring to keep the virus in check. California reported over the summer that it had reached its goal of 10,000 tracers, then dropped a contact tracing staffing threshold from its reopening metric.

But the pandemic has become much larger since, making even original contact tracing staffing targets too low, Watson said.

“Some states did get to that point, but a majority did not,” Watson said. “As a country, we’re halfway to the original projected need, which was 100,000 contact tracers. But I think that need has gone up much further with the surge in cases nationally.”

While tracing has effectively tamped down outbreaks in some smaller countries particularly in Asia, Watson said those countries have different levels of concern about privacy and trust in their government. Their citizens are more willing to disclose their health status and to use phone apps that let health officials trace people’s movement. In many parts of the U.S., case investigators have a hard time getting infected people and their contacts to speak with them.

“Other countries have taken a much more intrusive approach, in some cases that would not really be acceptable in this country,” Watson said.

In the Bay Area, however, health officials have encountered different barriers to contact tracing. In Santa Clara County, staffing far exceeded the state’s benchmarks and staff consistently report reaching 80% or more of cases and contacts within 24 hours of the positive test confirmation, an industry standard.

But Health Officer Dr. Sarah Cody said that while testing is widely available and turnaround times have come down, there are still lags of several days between an infection, test, result and contact by a case investigator. In many cases, the infected have no means to isolate from household members, or fear quarantining could cost them a job, she said. And because so many show no symptoms after being infected, they can spread the virus unknowingly for days.

Even so, she said, contact tracing remains an important tool. Santa Clara County has been doing reverse-tracing interviews to learn more about how the virus spreads by tracing infections back to their source.

“It’s one of several prevention strategies, it’s one layer among many,” Cody said. “It’s definitely necessary but not sufficient on its own. Testing is really important, cases investigation and contact tracing are really important, universal use of masks, staying home as much as possible — those other layers of prevention, we really need all of them working as well as possible to turn things around.”