The number of confirmed coronavirus cases in Marin has climbed to 53, with six new positive test results reported Tuesday. But the county’s deputy health officer warned that it’s likely there are many more undiagnosed cases due to a limited ability to test for the virus, and estimates that more than 1% of Marin’s population is infected.

“People are closely following our case counts, but I think that’s a gross underestimate of the activity of COVID-19 in our community,” Marin County Deputy Public Health Officer Dr. Lisa Santora told the county Board of Supervisors on Tuesday.

Santora said that only patients with moderate to severe symptoms of COVID-19 are being tested for the virus due to a shortage of test kits. But data from elsewhere in the world shows that the vast majority of people who contract the coronavirus have mild symptoms, she said.

“I think it’s very reasonable to expect that probably closer to 3,000 individuals in Marin County, or closer to 1% of our population, are becoming infected,” she told the supervisors.

In an effort to gain a better understanding of how the virus is spreading across the Bay Area, Marin County has joined six other jurisdictions in the region in issuing an order that mandates all labs to report COVID-19 testing data to health authorities.

In addition to Marin, the order was announced Tuesday in Alameda, Contra Costa, San Francisco, San Mateo and Santa Clara counties, along with the city of Berkeley, which has its own public health department. It requires academic, commercial and pop-up labs to report test results for all residents to both the health care provider and county officials.

Required data include all positive, negative and inconclusive results, along with identifying information like a patient’s name, sex, age, phone number, ZIP code and pregnancy status. Confidential health data would be shared with officials through a system known as CalREDIE and kept private.

Health officials have been hampered by a lack of data when it comes to tracking the growing pandemic, instead relying solely on the number of positive tests — which paint a woefully incomplete portrait of the virus’ reach.

Santa Clara County Health Officer Sara Cody in particular has called for better reporting in recent days, noting that the need for better data has increased as more commercial and pop-up labs come online.

“If we have both the positives and negatives, then we can have the denominator of who’s being tested, where we have hotspots,” Cody said.

Marin County has tested 527 people for the coronavirus at a drive-thru testing site the county set up on March 11 for patients referred by doctors. But county health officials said they don’t know how many were tested through private hospitals and commercial labs, only the number who tested positive.

Of those with confirmed cases of COVID-19 in Marin, 51% are between 35 and 64 years old, 30% are 65 or older, 15% are between 19 and 34 and 4% are 18 or younger.

Five Marin residents have been hospitalized due to the illness. There have been no reported deaths in the county.

Statewide, there are 2,102 confirmed cases of COVID-19 and 40 deaths, the California Department of Public Health said Tuesday.

Bay Area News Group contributed to this report.