Bernard J. Wolfson is a reporter for Kaiser Health News.

LOS ANGELES — Last Thursday, less than 24 hours after Los Angeles Mayor Eric Garcetti announced that the city was ready to provide free coronavirus testing for the 10 million residents of L.A. County, I decided to get tested myself — and to test Garcetti’s promise in the bargain.

I was surprised how easily I was able to log on to L.A.’s testing website. I answered a few questions, including whether I had any symptoms of the disease (no), and within three minutes I had a same-day appointment.

In fact, it was a same-hour appointment. The drive across a large swath of the county to the city-run testing site in non-pandemic times could easily have taken 90 minutes, but I got to the designated freeway off-ramp in under half an hour. That’s when the traffic jam began: It took 75 minutes to snake the additional half mile to a red tent at the Los Angeles Fire Department training center next to Dodger Stadium.

When I pulled up, a mask-wearing fire department employee handed through the car window a resealable plastic bag containing the testing materials — a cotton swab and a test tube holding a clear liquid. She directed me to one of three lanes up ahead, where I sat in my car and performed the test on myself.

I rolled the cotton swab in my mouth for 30 seconds, dropped it into the test tube, sealed the tube with a twist-on cap and placed it in the plastic bag. As I held the bag out the car window, a well-shielded attendant plucked it away with metal tongs and deposited it in a large blue bin.

I was among 10,000 Angelenos who visited one of the city’s eight testing sites that day — triple the number in previous days, when tests were limited to those with coronavirus symptoms or who were considered high-risk even if asymptomatic.

The mayor is proud of the program. At a news conference last week, after his tests-for-all announcement, Garcetti mentioned the praise he had received from doctors, public health officials and other mayors who, he said, told him, “Thank you for leading the way.”

But his plan is not a silver bullet. Although public health experts say it is vital to know how many people are carrying the virus, millions of Angelenos may choose not to get tested. And the testing program may provide a biased sample, since the results will be skewed toward people who have the time, inclination and transportation required.

What public health officials do with the results is crucial. In a process known as contact tracing, they need to follow up on the positive cases to reach friends, family members, colleagues and other contacts who may have been exposed. Officials must also find ways to safely isolate people who are infected.

Garcetti said positive tests for the novel coronavirus would be handed over to public health officials from Los Angeles County (which includes L.A. and over 200 smaller cities and unincorporated areas) for contact tracing and other follow-ups.

The county, saying that testing capacity is still tight, is sticking to the more restrictive policy of testing only those who are symptomatic or at high risk, which now includes people in essential jobs, such as health-care employees, first responders and food-supply workers.

Garcetti promised that the city’s test sites will continue to give priority to those groups, even as testing is opened to the general population, but he said the city has stockpiled 300,000 tests, with more on the way. Kyle Arteaga, a spokesman for the supplier, Curative Inc., based in San Dimas, Calif., said the company can meet L.A.’s expanded demand.

The city is paying about $120 per test, but the price could drop as much as 10 percent if there were a significant increase in volume — a million tests would likely cost the city between $110 million and $120 million.

The ultimate question about the testing program may concern the use of self-administered mouth-swabbing: The accuracy of those tests is not fully proved. A health-care worker plunging a six-inch swab deep into your nasal cavity is still the officially preferred method.

The reliability of the L.A. test suffers if you don’t cough forcefully a few times to bring up potentially virus-laden sputum before rolling that cotton tip around in your mouth. A four-minute video I watched before driving to the test site instructed me to do so, but there was no reminder when I got there and no staffers monitoring how people performed the test.

I think I did it correctly, though, so I am confident in the result that came back five days later: negative. But that only means I was “probably not infected” at the time of the test, the notice told me. And it cautioned that I can still be exposed to the virus at any time. I still see lots of hand-washing and social distancing in my future.

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