Coronavirus testing: Everything you need to know

Public health experts agree that widespread testing for the coronavirus, officially known as COVID-19, is the best way to prevent the spread of the disease and lift nationwide quarantines.

And many say the U.S. isn’t doing nearly enough testing.

“Testing is the only way — or our best tool, apart from these dramatic public health measures — to make sure we don’t risk second waves anywhere in the U.S.,” Dr. Mark Cameron, an immunology professor at Case Western Reserve University, told Digital Trends.

Coronavirus is wreaking havoc on the world, and will continue to for months to come — but what exactly are we doing to fight it? Have we made any progress on a vaccine? Here’s what you need to know
coronavirus taiwan asia technology success science researcher getty

Although there are dozens of labs processing thousands of tests a day, the U.S. is still unsure exactly how many people have the coronavirus. The country needs to have a much better sense of that number before it begins lifting lockdowns, according to health experts.

The Food and Drug Administration started authorizing some test-makers’ at-home products amid a mass shortage of testing. That lack of testing leaves many questions unanswered: What percentage of the population has been infected? How many people get the virus but never develop symptoms? Who is immune if a second wave strikes?

Testing can help give us better answers and more clues about the virus itself. Here’s what testing means, why it matters, and how it could help America and the world re-open.

What types of tests exist?

There are currently two main forms of tests: Swab and antibody tests.

The swab test, the one most commonly used, is administered to people currently displaying symptoms.

The second type of test is used with those who may have recovered from the illness. This antibody test can determine if their immune system created proteins to fight the virus.

“Those two tests can work in tandem if we are to learn all that we can about who has the virus today or who has already been infected,” Cameron told Digital Trends.

“People want a fast answer and a fast cure, but it’s not that easy,” said Dr. Laila Woc-Colburn, an infectious diseases professor at Baylor College of Medicine.

How does swab testing for the virus work? 

The most common swab test uses a technique called reverse transcription-polymerase chain reaction (RT-PCR). A health care worker may take a nasopharyngeal (NP) swab, using a long fiber and plastic instrument to go through the nose to the back of the throat. The CDC has recently allowed testing with nasal and throat swabs, but the NP is preferred and the only type approved for asymptomatic patients.

“Each one of those sample tests has a different level of sensitivity,” said Cameron. The goal is to collect mucus and cells — anything that may contain the virus.

Once the health care worker has the sample, the virus’s RNA is extracted and transcribed, using enzymes, into DNA. The DNA gets copied multiple times, and complementary fragments of DNA are also added to the mix. When the copied DNA binds to these fragments, chemical markers are released that glow. If there’s a certain amount of fluorescence, that means the virus is present.

The instruments used to replicate the DNA are PCR machines. They come in various sizes and can take several hours cycling through different temperatures as part of the process. There are smaller diagnostic machines, like the ID Now from Abbott labs. It can perform a test in as little as five minutes, but it can only do one sample at a time. The larger machines take longer but some can hold hundreds.

Are there false positives or negatives?

These tests don’t seem to be producing many false positives.

“The good news is that the tests appear to be highly specific: If your test comes back positive, it is almost certain you have the infection,” Yale University health care researcher Dr. Harlan Krumholz wrote in The New York Times.

False negatives remain a problem. Some estimates put their error rate as high as 30%, meaning the test comes back negative, even when someone has already contracted the virus. Tests include warnings that “a negative result does not rule out COVID-19 and should not be used as the sole basis for treatment or patient management decisions.”

There are many reasons for the high false-negative rates. Some may be due to an incorrectly collected sample, but people may also be getting tested before the virus is detectable. Perhaps they’ve only recently contracted it, or their immune system is doing a good job of keeping it at bay. “Once you have fever, you’re probably going to have a positive PCR,” said Woc-Colburn. “So that takes about five to seven days.”

Some hospitals are using CT scans to diagnose COVID-19 when swab tests come back negative but patients are still exhibiting symptoms. It’s an effective method, said, Woc-Colburn, “but you don’t want to be CT scanning the whole population. First of all, because it’s expensive and it takes about an hour to scan someone, plus you expose them to radiation.”

How do antibody tests work?

With an antibody test, researchers analyze blood samples for the proteins the immune system produces in response to an infection.

Different antibodies are produced at different stages of infection; immunoglobulin M (IgM) is the first and starts appearing between four and 10 days after infection. Immunoglobulin G (IgG) are the antibodies that “remember” viruses and can more quickly mobilize the immune system in future encounters. These can be detected after 10 to 14 days, if not longer; however, these timelines may be different for COVID-19 patients.

The Food and Drug Administration has authorized several antibody tests for use where antibodies in the blood bind to the test’s antigens, which are similar to the virus’s molecules. That should only happen if antibodies are present, meaning the person was exposed to COVID-19. Yet Cellex, one of the FDA-approved tests, has a false positive rate of 5%, according to The New York Times.

And the World Health Organization recently warned that antibody tests don’t prove immunity.

“The problem with an antibody test is that it can capture a lot of viruses, so it’s a polyclonal,” said Woc-Colburn. “You can actually capture the common cold that a lot of us get.”

The two viruses are related enough that antibodies your body produced to fight the cold could bind to the test’s antigens. “So, you want to have what we call a monoclonal, which is specific to a region of the virus,” said Woc-Colburn. That would cause fewer false positives.

“That’s the test that has to develop much more than it is today to be an accurate tool for us to use to track people who have had the virus,” Cameron said.

It’s also unclear how long these antibodies will stay in the body or how long a person would remain immune or resistant to a second infection with the virus. “Right now, we’re speculating that maybe six months” is how long immunity will last, said Woc-Colburn. “It could be longer, but we don’t know.”

How many people have been tested in the U.S.?

The U.S. is testing an average of 147,000 people per day, according to the COVID Tracking Project. Thus far, the site puts the total number of people tested at over 4 million. These numbers are just estimates, and it gives better data reliability grades to some states over others.

How many people should be tested?

As some states start to ponder reopening their economies, experts and officials warn that more testing should be one step in the plan. Before easing lockdowns, cases should be declining, according to many public health guidelines, including the World Health Organization.

As of April 21, states from Alabama to Wyoming were still reporting new cases.

The Kaiser Family Foundation recently looked at different benchmarks for how many tests the U.S. should be doing before it can ease social distancing orders. They range from 2.6 million to 161 million a week.

“But at the end of the day, what we found is no matter which benchmark you choose, the U.S. is way behind on what it should be doing,” said Dr. Jennifer Kates, senior vice president and director of global health and HIV policy at KFF.

Right now, the majority of people being tested are the sickest. “Those asymptomatic cases are the ones that we have to be particularly concerned about, because they’re almost certainly not going to get tested unless we’re testing everybody,” said Cameron. “And they are the ones able to spread the virus in the meantime.”

How can I get a COVID-19 test?

Due to a shortage of tests, personal protective equipment, and other supplies, states have been limiting who’s able to get tested. Many have been restricting testing to health care workers and vulnerable patients with serious symptoms. “If you’re not on that priority list, you probably won’t get a test,” Cameron said.

The FDA has warned that fraudulent tests are flooding the market.

Right now, the safest course of action for dealing with a lack of COVID-19 testing is paradoxical: If you’re currently sick and think you have it, act like you’re infected and quarantine yourself. If you’re not sick but suspect you already had it, act like you didn’t and remain socially distant.

For the latest updates on the novel coronavirus outbreak, visit the World Health Organization’s COVID-19 page.

Editors' Recommendations