Health experts say widespread testing for the novel coronavirus is key to containing its spread and helping counties make decisions about reopening as the pandemic continues.
Previously, shortages of swabs, reagents and other materials limited testing to people with more severe symptoms or to those with high risk of exposure. But now that these supplies are more readily available, Bay Area counties have ramped up testing and loosened criteria so that more people can learn if they are or have ever been infected with the coronavirus, the pathogen that causes COVID-19.
But just because more people in the Bay Area can get a test, does that mean everyone with access should? We asked medical experts who should get tested for COVID-19, when to get tested, and what the results can and can't tell us.
- First: Which Test — Viral or Antibody?
- Who’s Eligible for Coronavirus Testing?
- Who Needs to Get Tested? Should I?
- What About Mild Symptoms?
- What Does a Negative Test Mean?
- I Want to Visit Relatives, Should I Consider Getting a Test?
- When Should I Get Tested After a Protest?
- What Should I Do If I Test Positive?
Viral tests, often called PCR or RNA tests, are typically administered by taking a swab sample from the back of the nasal cavity or throat. This can detect if your body is shedding virus — that is, if you currently have an active SARS-CoV-2 infection.
Experts say to keep in mind that it generally takes about five days after infection before it registers as positive, and you can still be exposed after you’ve been tested. So doctors say a negative PCR test result doesn’t mean you should let your guard down.
Antibody, or serology, tests, screen the blood for specific COVID-19 antibodies. These are proteins the immune system makes to fight the virus. Antibodies can take one to three weeks to build up, but are still detectable after patients recover from infection.
Antibody tests can reveal if you already had the virus, even if you didn’t have symptoms. But experts don’t know for certain how protective COVID-19 antibodies are against future infection, so a positive test for antibodies doesn’t mean you are immune to the virus.
Neither viral nor antibody tests are 100% accurate. Research suggests PCR tests may miss positive cases about 20% of the time. The Food and Drug Administration now provides performance results for antibody tests from different manufacturers.
The Centers for Disease Control and Prevention has posted guidelines for diagnostic testing on its website.
In the Bay Area, a growing number of county health departments — including Santa Clara, Contra Costa and Solano — offer COVID-19 tests to all residents regardless of symptoms, and these are free if you don’t have insurance. Others, like San Francisco and Marin, require at least one symptom or some risk of exposure.
Many hospital clinics, private labs and health care providers like Kaiser and One Medical offer testing as well. Pop-up sites and community testing programs through Verily’s Project Baseline provide additional avenues to get tested. Bay Area health departments have been working to increase testing in underserved communities, though gaps still exist in the Bay Area and across the state.
Who Needs to Get Tested? Should I?
“We need to be able to test people with symptoms, and contacts of people with the virus,” said Dr. Bob Wachter, chair of the Department of Medicine at UCSF.
Groups that experts say should get tested include medical and other front-line workers, vulnerable populations, and those who have attended mass gatherings like protests. Also included are those who have come into contact with a lot of other people, perhaps while commuting or at work.
Some hospitals, including UCSF and Stanford, test patients who are getting a medical procedure or are hospitalized with another illness. Wachter says testing a portion of people without symptoms will help public health experts anticipate a surge in cases.
But he doesn’t see a good reason for people who don’t have symptoms and are following stay-at-home orders to seek out a viral test. This is in part because the chances are low that a person without symptoms in the Bay Area has been infected with or is spreading the coronavirus.
Only around 1 in 250 patients at UCSF without COVID-19 symptoms have tested positive for SARS-CoV-2, he says.
Dr. John Swartzberg, clinical professor emeritus at UC Berkeley School of Public Health’s infectious disease division, said, “The more testing we do on a daily basis, the more accurate our numbers will be.”
But Swartzberg agrees that not everyone needs a COVID-19 test. Public health departments, he says, can monitor cases by testing a representative sample of the population in line with the state’s goal of 200 tests a day per 100,000 residents. Researchers in the Bay Area are also screening large communities like San Francisco’s Mission District to find out what percentage of people have the virus.
If you’re healthy and practicing social distancing, Swartzberg said, “There's really not a particular value in screening to learn about yourself.”
There’s “no hard and fast rule” about when a symptom becomes serious enough to warrant a test, says Dr. Yvonne Maldonado, professor of pediatrics, epidemiology and population health at the Stanford School of Medicine.
She recognizes this can be tricky to navigate for people with mild symptoms, given the source of a sore throat or runny nose could be something unrelated to the coronavirus, like pollen allergies.
But people with a fever, difficulty breathing or multiple or persistent symptom should arrange for a test, she says.
“If you [just] have an itchy throat, probably not,” Maldonado said. “If you have an itchy throat and that night you develop a low-grade fever, yes, get a test.”
Testing those with less serious symptoms, Maldonado says, can prompt people to isolate sooner if they have the virus. It can also help patients seek medical attention more quickly if symptoms progress.
If you’re on the fence about needing a test, Maldonado says you can wait a day or two and self-monitor while you keep socially distanced or call your health care provider for advice.
Wachter says that because PCR, or RNA, test results only show whether or not patients currently have COVID-19, there’s a limit to how you should use the information.
It can take three to five days, he says, between when you are exposed to when you would test positive. In some cases, the incubation period can last up to 14 days, and a patient could test negative during this “presymptomatic” period. The test also can’t account for any future exposure.
“A week from now, that test that you had today that was negative means virtually nothing,” Wachter said.
Getting one negative PCR test, he says, shouldn’t give people a license to disregard social distancing practices, stop wearing masks or socialize in large groups. This, he says, would only increase the chances of getting the virus.
Wachter also cautions that PCR tests can also give false negatives.
“If you do have it, it'll pick it up maybe four out of five times, meaning it's going to be wrong one out of five times.” he said.
Wachter says it all comes down to probabilities. Getting a negative test significantly, but not entirely, reduces the chance you have the coronavirus for at least a few days.
Some health experts say yes, this is one scenario where a person without symptoms should consider getting a test.
“If I was on the fence about visiting and I had a negative test in the last couple of days, it might get me to leave the fence and go,” Wachter said. “But it would not lead me to give them a hug and a kiss, and I would still sit six feet away, and I would still wear a mask.”
Maldonado says given the choice between driving or flying to visit her 87-year-old dad, she would elect to drive. If you have to take a flight, she recommends getting tested beforehand and again about five days after arrival to make sure you weren’t exposed en route. In between tests, she says, she would “be very careful” and follow social distancing guidelines.
In this scenario, Maldonado says the risk that you have or are spreading the virus “is extremely low, but it's not zero.” You’ll also want to get a test about five days after your return, she says, or be committed to isolating for a few weeks.
If you are at a protest or other mass gathering and get tested immediately after, that will likely be too soon for the test to detect the virus. Maldonado says people should instead wait about five days before getting a test.
“If you are being careful and you're generally wearing a mask around other people and socially distancing, washing your hands, you're probably not going to transmit,” she said. “But I would say by day five after exposure, I would consider getting a test at that point.”
For many of the questions about travel, mass gatherings and testing, Maldonado says there are no firm answers. Rigorous studies, she says, will ultimately be needed to provide more clarity.
If you don’t have symptoms and receive a positive test, the CDC and many health care providers say the best practice is to self-isolate for 10 days. At this point, provided no symptoms develop, Wachter says, it would be unlikely that you have an active infection you could spread to others. But regardless, you would want to follow recommended social distancing guidelines.
A follow-up test is generally not required in this case, he says, and some people continue to test positive after they are recovered and no longer contagious. The CDC says your health care provider can provide guidance and, “If you will be tested, you can be around others after you receive two negative test results in a row, at least 24 hours apart.”
For people with symptoms and a positive test, CDC guidance is to remain isolated until you have gone three days without fever and 10 days since symptoms first appeared, provided the symptoms have improved.