LOS ANGELES — The difficulty finding coronavirus test kits in many parts of California and delays in getting results are causing increasing frustration and contributing to the surge of infections that in just two weeks more than doubled the number of people in hospitals with COVID-19.

Negative test results can be a necessity for any number of activities, from going to work to boarding an airplane or attending a sporting event. Delays in getting results — or inability to find a test kit — can mean people with very mild or no symptoms may presume they are not infected and go about their usual routines.

“If you are tested and you’re positive then you know you need to isolate,” said Abraar Karan, an infectious diseases doctor at Stanford University. “If you can’t get tested, and you don’t have the luxury to just quarantine without knowing, sure, you may have people going out and infecting others.”

The surge of cases in California has led to a soaring demand for tests that in many places simply can’t be found. Some county mail-in testing programs have been halted due to exploding demand. In places where tests are available, people sometimes have to wait in line for several hours.

Gov. Gavin Newsom announced Friday that he is activating the California National Guard to add testing sites and boost capacity. More than 200 guard members are being deployed to 50 sites to help with clinical staffing and crowd control, the governor said.

There’s also been a lag in obtaining test results. Kirsten Bibbins-Domingo, an epidemiology professor at University of California, San Francisco’s medical school, said she heard one lab was taking nine days to return results — longer than someone exposed to COVID-19 may have to quarantine.

“If you are trying to do the right thing, and you decided to wait in line to get a test, having a long time to get actionable information is not helpful,” she said. “It’s sort of absurd.”