Experts and officials say that increased testing is essential to protect medical workers and patients, to understand how widespread the coronavirus is in the United States, and to help understand how concepts like herd immunity apply to the coronavirus.

The First Responder COVID-19 Guide app is one of several new technology initiatives to connect people at high-risk for COVID-19 infection with testing.

Here's how it works: Users take a survey with questions about their symptoms. If they have symptoms suggesting COVID-19 infection, the app recommends testing. First responders can take that result to the contact at their workplace in charge of health, referred to as a "department infection control officer" inside the app, and get scheduled for priority testing at a Stanford Health Care site.

A new app from Stanford Medicine built with Apple 's help will help connect firefighters, police officers and paramedics in California to drive-through COVID-19 testing if they are showing symptoms of the coronavirus.

Stanford is starting with police officers, firefighters, and paramedics because they're essential and are at high risk of catching the virus. As of April 1, more than 1,000 New York City police officers had tested positive for COVID-19, for example.

"If we have a first responder who has symptoms, it's really important for them to get screened and potentially test it because they're going to be very patient-facing and very community-facing. That's what their jobs are," said Dr. Bob Harrington, chairman of the Stanford Department of Medicine.

The app is currently only available in Santa Clara and San Mateo counties in California.

Increased testing is important in California, which has tested fewer people per capita than other hard-hit states like New York or Washington. Stanford said it has the capacity to test 2,500 patients a day and turn around the results within hours. It wants to test more and "crank it up." But, it still has limited access to testing kits, Harrington said.

The team at Stanford Medicine hopes to expand it to more frontline workers, including grocery store workers and government employees. After that, they want to make it, or similar apps, available in additional counties and states.

Stanford has conducted more than 3,000 COVID-19 tests after it developed its own test in March. It found it's able to conserve resources and supplies by screening people through video visits before they take a test. The app is making that process more efficient.

"About half of people actually screened out. We thought they could go home and come back if symptoms worsened. But about half we ended up testing," Dr. Harrington said.

Apple helped Stanford Medicine with some of the development, Harrington said. The app uses Apple's ResearchKit and CareKit software, which are designed to help developers handle sensitive medical data. All data from the app stays on the patient's device unless they share it with a health provider, Stanford said.

Alphabet subsidiary Verily also built software to direct people with COVID-19 symptoms to testing sites. Last month, it launched in Santa Clara and San Mateo counties, and has since expanded to Riverside and Sacramento counties. Apple released a COVID-19 app with a screening survey that Americans can download, but it does't direct users to test sites.