As new and more contagious variants of the COVID-19 virus emerge in California at a troubling rate, testing for the pathogen has plummeted, challenging the state’s effort to trace their spread, discover outbreaks or detect whether they are eluding our vaccines.
Rates of testing have fallen by more than 60% since January’s peak, according to the most recent data by the California Department of Public Health. Statewide, a total of 186,112 tests were reported on March 31, down from 477,718 on Jan. 4.
The precipitous decline is reflected in Bay Area data, as well, falling about 40% in Santa Cruz County, 30% in Santa Clara, Contra Costa and Alameda counties and 25% in San Mateo County over the past three months. Testing is also down nationally.
“If we are not testing robustly in the community, it narrows our view of where the virus is circulating, and to what level it is spreading,” said Dr. Marty Fenstersheib, COVID-19 Testing and Vaccine Officer for the County of Santa Clara. “Testing also allows us to break the chains of transmission and reduce spread, which gives the virus less opportunities to replicate and mutate.”
The decline in testing is understandable: as cases decline, fewer of us fear exposure. Vaccines are more widespread. And we’re weary of testing, after the year-long pandemic, said experts.
Yet as testing falls, the number and diversity of viral variants is climbing.
In the past week, the number of California cases involving a variant first discovered in Britain grew from 851 to 980. Cases caused by California’s two homegrown versions of the virus — B.1.427 and B.1.429 — also increased, jumping from about 9,000 to 12,500.
Additionally, there has been a tiny uptick in cases involving the worrisome Brazilian variant, which is less responsive to treatment, and the South African variant, which evades vaccines. On Wednesday, Stanford University reported a total of six confirmed cases in the Bay Area of another new form of the virus, whose emergence in India is coinciding with a surge in cases.
But the reduction in testing means even these startling numbers may undercount the true number of infections circulating throughout the state, experts warn. Does California really have about 2,000 new cases a day, as reported, or is that number artificially low?
“Without population-based testing for public health surveillance purposes, it’s like flying blind,” said infectious disease expert Dr. Gary Schoolnik, a clinician and professor of medicine at Stanford Health Care.
But because the virus is likely to become endemic – persisting in small pockets of the population, even as vaccines limit its spread and blunt its effects – we must continue to monitor it, say experts.
We’ve rarely had a disease where so many people are asymptomatic, yet transmit it to others, said Mara G. Aspinall, professor of biomedical diagnostics at Arizona State University. “That’s why we need to have a systematic approach to regularly test people.”
Testing remains important even as more Californians get vaccinated, said Aspinall. That’s because it can detect “breakthrough” cases, where a vaccine fails to protect against infection. Although California does not release data on these incidents, this week Oregon and Washington reported 168 and 102 of those cases, respectively.
“It’s critical to help vaccine manufacturers understand, quite specifically, what variants are out there, what do they look like, how the virus is changing and how can we ensure that we design around it,” Aspinall said.
Testing could also reveal if, over time, vaccines’ protective immunity starts to fade, and cases start to climb, according to Dr. Peter Piot, director of The London School of Hygiene and Tropical Medicine.
To be sure, there is growing availability of quick diagnostic tests, used by doctors to find infections in people who feel sick.
There is also greater access to so-called screening tests, used to test people at school, work, sporting events and other public gatherings. Some aren’t very accurate but are cheap and provide near-instant results, so are ideal for routine and frequent use. Others, such as a new handheld PCR test made by the San Jose company Visby Medical, can deliver near-perfect results in 30 minutes.
In certain settings with vulnerable populations — such as the elderly or people with weakened immune systems due to cancer treatment, dialysis or organ transplantation — frequent screening could serve as a sentinel for trouble, said Schoolnik.
What’s more challenging, yet critically important, is a different approach: testing and sequencing conducted by county and state health officials, called “genomic surveillance.”
The state is striving to sequence 2% to 5% of all positive cases from a representative sample of communities, through a network of partner laboratories called COVIDNet. California is doing better than most other states; nationally, only about 1% of cases are sequenced. More and more labs across the state have begun to sequence at least some of their positive specimens, according to the California Department of Public Health.
Ideally, say experts, California would test a much larger and more representative sample of the state’s gender, age, racial, ethnic, socioeconomic and geographic diversity. Viral samples could be geotagged and time-stamped.
This isn’t diagnostic testing, so the findings may not be reported back to doctors or patients, said the California Department of Public Health.
But better surveillance can help health officials decide where and when to respond to finally beat the pandemic.
“One secret weapon has helped beat every disease outbreak over the last century — but it is not masks or social distancing, lockdowns, or even vaccines,” according to a new report from the Rockefeller Foundation, which provides a blueprint for dramatically expanding the nation’s genomic surveillance.
“Instead, it is data.”
