A unique, early coronavirus testing program in Santa Clara County helped officials recognize the crisis and respond with the country’s first shelter-in-place order, according to a new report from the Centers for Disease Control and Prevention.

But just as experts say it highlights the importance of early and widespread testing, the study also underscores how the state comes up short in its testing capacity.

On March 5 — when Santa Clara County had reported just 21 cases of COVID-19 and wasn’t testing anyone unless they had traveled abroad to a coronavirus hotspot or had been in contact with a known infected person — health officials began their “sentinel surveillance” study. Spooked by the first known case of the virus spreading by community transmission in the county a week earlier, they decided to hunt for more such cases.

Between March 5 and March 14, officials began taking data from four urgent care centers in Santa Clara County. The researchers looked at 226 patients who complained of respiratory symptoms but had no travel history to coronavirus hotspots or known contact with an infected person. Of those, 23 percent tested positive for influenza. Among the patients who tested negative for influenza, the researchers had the capacity to test just 79. Of those, 11 percent — or nine patients — tested positive for COVID-19.

Based on that data, the researchers estimated that 8 percent of all patients with respiratory symptoms at the four clinics had COVID-19. That was a startling finding.

“It’s important because it shows that there is transmission of the disease in the community, and that the disease was perhaps more widespread than previously understood,” said Dr. George Han, deputy health officer for Santa Clara County and the senior author of the CDC report. “And because of that, we were able to use that data as one piece of data to inform our decision about making recommendations and orders to the general public.”

Coupled with the ever-growing number of coronavirus cases reported, the new data spurred county officials to act. On March 16 — just two days after the study ended — Santa Clara County joined five other Bay Area localities to issue the first-in-the-nation stay-at-home order. Three days later, California Gov. Gavin Newsom made it a statewide mandate.

But because testing capacity was so limited, the Santa Clara County researchers could not test every patient who fit their criteria. Instead, they tested the first five to 10 patients who fit their criteria each day, and then stopped. The result was a small study with a limited sample size.

“That’s why we need a national strategy to ramp up the production of testing materials and testing kits,” Han said, “so that we can get a better handle on controlling this epidemic.”

Brian Schwartz, a professor of medicine in the division of infectious diseases at UCSF, agrees.

The study was “reinforcing the idea that we have not been doing enough testing, and we haven’t been doing it early enough,” he said. “And when we do it, we pick up cases.”

Han hopes other communities around the country, especially those that haven’t yet seen many confirmed COVID-19 cases, will run similar “sentinel surveillance” programs.

Santa Clara County already is discussing conducting another similar study in partnership with other Bay Area jurisdictions.

“I think this is something that health departments across the country are interested in because it helps inform what is going on in their communities,” Han said. “But it does take resources and time to set up.”