Public health experts agree that widespread diagnostic testing is the first step toward lifting social distancing orders and adjusting to a new normal post COVID-19.
To reopen the country, states must be able to test at least everyone with COVID-19 symptoms. Estimates on how many tests the U.S. would need to conduct range from 750,000 per week to millions every day.
Delays in testing in February forced the U.S. to play catch-up, and the majority of testing has been conducted by private labs instead of those owned by the government.
Below are key questions and answers surrounding diagnostic testing, including why there is a testing backlog, how COVID-19 tests are conducted and why saliva tests are better for healthcare workers.
Why is there a backlog in diagnostic testing?
Though President Donald Trump declared the coronavirus a national public health emergency on Jan. 31, only the CDC was allowed to conduct COVID-19 testing and only 12 labs in the U.S. were capable of diagnosing the virus until Feb. 29, according to The New York Times.
In early February, the CDC shipped about 200 test kits to states, but in mid-February the agency said the tests were flawed and shouldn't be used. It told state health departments to send all test samples to the central CDC lab in Atlanta, delaying the results of those tests by several days.
Both the CDC and FDA could have allowed a diagnostic test approved by the World Health Organization to be used in the U.S., but both agencies chose not to, the Times reported. It is unclear why the agencies declined to use the test, and a CDC official who wished to remain anonymous told the Times: "In retrospect, it seems like a bad decision."
The CDC also limited testing to people who had traveled to China in the previous 14 days or who had contact with someone with a known coronavirus case. The agency later broadened the criteria to anyone who traveled to countries with coronavirus infections, but positive results still had to be reconfirmed by the central CDC lab in Atlanta, according to the Times.
On Feb. 29, the FDA said it would allow private labs and hospitals to develop and use diagnostic tests.
Labs owned by states, universities and private companies can now apply for emergency approval for tests and are allowed to use the tests as soon as they've submitted evidence that the tests work.
Why has diagnostic testing fallen on private labs instead of public labs?
Private labs have conducted more than 85 percent of all COVID-19 tests in the U.S. because public labs owned by states aren't designed to handle large volumes of tests, according to NBC News.
"The state's public health lab is not intended to be a high-throughput clinical diagnostic lab," a government spokesperson in Virginia told NBC. "Our role is to implement tests early on to help identify an emerging disease and then to support public health efforts, including surveillance and outbreak investigations."
New Jersey's public lab can process about 70 tests per day, New York's can process about 1,000 and Pennsylvania and Alabama can each process about 300 per day, according to NBC.
Since public labs can't meet demand for diagnostic testing, the burden has largely fallen on private labs.
Quest Diagnostics, one of the country's largest private diagnostic labs, based in Secaucus, N.J., has conducted 800,000 tests as of April 13 and has increased its testing capacity to 45,000 tests per day.
What's the difference between diagnostic tests and serological tests?
Diagnostic tests are molecular tests that detect the virus' genetic material using samples that typically come from a patient's respiratory system, according to the FDA. They are used to determine whether a patient has COVID-19.
The FDA has approved 34 different diagnostic tests for COVID-19 as of April 13.
Serological tests, also called antibody tests, measure the amount of antibodies present in a patient's blood when the body is responding to an infection, such as COVID-19. These tests detect the body's immune response to the infection rather than detecting the virus itself.
Serological tests can help healthcare professionals identify who has recovered from COVID-19. The CDC has said that as many as 25 percent to 50 percent of people with COVID-19 might not show symptoms, so serological tests can help determine the full spread of the virus.
More than 90 antibody tests are currently on the market, but only one, manufactured by Cellex, has been approved by the FDA, according to Politico.
How are COVID-19 tests conducted?
Most diagnostic tests are conducted by a healthcare professional using swabs to collect biological samples from a patient's throat or nose.
This puts healthcare professionals at risk of contracting the virus, as well as puts a further strain on medical supplies, as professionals have to change their gloves and masks after being in contact with a patient who may have the virus.
Diagnostic tests are conducted both in hospitals and in various drive-thru sites across the country.
Serologic tests are conducted by drawing blood from patients and looking at the antibodies in their blood.
What is the new saliva test and why is it better for healthcare workers?
The FDA April 11 approved the first saliva test, developed by researchers at New Brunswick, N.J.-based Rutgers University, Spectrum Solutions and Accurate Diagnostic Labs, a private lab in New Jersey.
To take the test, patients spit into a test tube several times and then give the tube to healthcare professionals to process, according to The Hill.
Public health experts said the tests will allow for a broader population to be screened because it doesn't require swabs and will reduce health professionals' risk of contracting the virus, as they don't have to come in direct contact with patients while the sample is being collected.
Saliva tests could also ease the strain on medical supplies, as healthcare workers don't have to go through as many gloves or masks to conduct the tests.
Will antibody tests allow the U.S. to reopen?
Not necessarily.
Just because someone has COVID-19 antibodies doesn't mean they're immune to it. Scientists still don't know if COVID-19 antibodies lead to immunity as antibodies do for other types of viruses, Politico reported.
However, widespread antibody testing would allow experts to determine who's been infected, which is the first step to stopping the disease from continuing to spread. Health experts have agreed that antibody testing is essential for easing social distancing measures and allowing people to return to work.
So far, very few Americans have undergone antibody testing, though HHS members have said "tens of millions" of antibody tests will soon be under production, according to Politico. It's unclear when those tests will be available to the general public.
The Trump administration has said it would require most private insurers to cover COVID-19 antibody testing at no cost to consumers, as it has with diagnostic testing, according to Politico.
Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, has suggested issuing "immunity certificates" to people who test positive for coronavirus antibodies to allow them to return to work.
However, some public health officials are concerned this method could incentivize people to try to become infected.
"I worry about the consequences for public health if people decide that their employment rests upon getting this disease," Gigi Gronvall, an associate professor of immunology at the Johns Hopkins Center for Health Security, told Politico.
Allowing some people to return to work could also cause others to take social distancing measures less seriously.
Antibody tests can also identify which people can donate convalescent blood plasma, which can be used to treat severely ill COVID-19 patients.
The FDA has said it will allow patients with severe COVID-19 infections to be given convalescent plasma, which are antibody-rich blood products taken from blood donated by people who have recovered from COVID-19, though it hasn't been proven the method would treat COVID-19.
The method has been used for other viral outbreaks, such as for measles, polio, pumps and influenza, and has been used in China for some COVID-19 patients, according to Beaumont Health.
Beaumont Health, based in Royal Oak, Mich., said April 14 it is starting the country's largest serological testing study, aiming to determine the total population with COVID-19 antibodies across the health system, which has 38,000 employees.
The study will help answer questions such as how susceptible healthcare workers are to acquiring COVID-19, the relationship between antibody levels and severity of the disease and whether COVID-19 antibodies protect you from new infection.
Where do we stand now?
As of 12:30 p.m. CDT April 17, the U.S. has tested 3,423,034 people for COVID-19 with 686,991 testing positive, according to data from Johns Hopkins University.
From April 12 to April 16, the U.S. tested an average of about 147,000 people per day, according to the COVID Tracking Project.
Shortages of supplies needed to conduct COVID-19 tests, such as cotton swabs, have been one of the biggest obstacles in expanding testing. The FDA approved April 16 a new type of polyester-based swab to be used for testing that should be cheaper and easier to manufacture.
CMS also doubled what it pays to hospitals to run COVID-19 tests this week in an effort to speed up testing.
Editor's note: This article was updated at 4 p.m. on April 17 to reflect current testing figures.