BARELY MENTIONED in President Trump’s Oval Office address on Wednesday night was the diagnostic testing fiasco. He said only that testing capability is “expanding rapidly day by day.” He should have addressed what has become a major failure in how the United States has responded to the coronavirus pandemic, leaving the country far behind other nations in testing for and controlling infection. With so few tests, the United States has been flying blind into a storm.

Why is this such a problem? We cannot expect a vaccine or cure for covid-19 in the immediate future. But widespread diagnostic testing could help dramatically.

As Jeremy Samuel Faust, an emergency physician at Brigham and Women’s Hospital, wrote in a Post op-ed, this is for two reasons. First, identifying even mild cases of the infection that are now going uncounted would yield a more accurate picture of the lethality of the disease. This in turn would likely reassure the public and financial markets.

Second, Dr. Faust explained, “the discovery of mild and symptom-free cases may lower the number of serious cases over the course of the outbreak, and might even save lives.” This is partly because treatment (short of cure) can be effective, and partly because isolation of asymptomatic patients would slow the spread of infection. But those patients aren’t going to self-quarantine if they don’t know they’re sick.

South Korea’s experience supports this argument. Regulators there approved a new diagnostic test by a private company in a week’s time. South Korea is testing 20,000 people a day, and it now has drive-through testing — and the infection rates are not climbing sharply.

The United States’ record is sadly different. The initial setback was a technical fault in the diagnostic kits created and sent to state public health labs by the Centers for Disease Control and Prevention in February. While the CDC rushed to troubleshoot, only about a dozen state labs could test, and all other samples had to be sent to the CDC in Atlanta. Test results took days. On top of this, the agency set very restrictive criteria for who would be tested: only individuals who showed respiratory symptoms and had either recently traveled to China or come in close contact with an infected person. On Feb. 29, facing a rising case count in the United States and a lack of testing, the Food and Drug Administration abruptly changed its rules to allow “high-complexity” laboratories to use diagnostic tests they designed in-house. This began to expand testing and allow hospitals and private firms to produce them — they are now the main hope of ramping up testing — although another looming glitch is a shortage of chemicals.

Not all the testing problems in the United States are political, but it certainly did not help that Vice President Pence repeatedly over-promised the availability of tests, touting millions when only thousands have been conducted. “Anybody that needs a test gets a test,” Mr. Trump declared on March 6 at the CDC headquarters. “They’re there. They have the tests. And the tests are beautiful.” For the sake of the ill and the healthy, we hope the reality will soon catch up to that idle boast.

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