Over the last month, drive-through swab collection sites have popped up around the region, and dozens of big diagnostic companies have begun selling coronavirus molecular tests.

Yet you haven’t been able to get one. Why?

Short answer: Because demand vastly exceeds supply, and that isn’t going to change any time soon.

Here’s what’s behind the testing bottleneck.

Shortages

When U.S. coronavirus testing began on March 4, the country had practically no capacity, because the federal government was the only source of testing kits, and the kits it sent to state labs were initially few and faulty. Now, the government has authorized emergency use of molecular tests developed by Roche, LabCorp, Quest, Cepheid, and 17 other companies — more every day. But the list of shortages that hamper testing has only grown: cotton-tipped swabs, protective equipment for workers taking those swabs, fluid to ship viral samples, chemicals used to extract and copy the virus from those samples.

The three international companies with a corner on the market for those chemicals have very short supplies because “there’s global demand,” said Kelly Wroblewski, director of infectious disease programs for the Association of Public Health Laboratories. She added that some workarounds exist, but these would reduce the accuracy of the test by increasing the rate of missed positive cases.

Technology

The ideal diagnostic test would be used near the patient and give results in minutes — not days or a week, as with the laborious coronavirus process. Abbott Labs and Cepheid are offering such rapid, point-of-care tests for the coronavirus, but the tests can be processed only on the company’s testing “platform" — an expensive, automated molecular analytical machine. “Not every hospital or lab has these machines,” said Ed Winnick, editor-in-chief of 360DX, which reports on the clinical diagnostics industry. “It speaks to the fragmented nature of diagnostic testing in this country.”

Treatment, or the lack of it

In a hospital, diagnosing coronavirus patients is critical for preventing the spread of the virus to health-care workers and other patients. But in many communities, the virus is so widespread that the only way to avoid it is to stay home and shun people. For those at home who develop mild symptoms — say, a fever and cough — testing is of limited value. A positive result won’t change treatment (which is basically over-the-counter flu medicines), and going out to get the test has exposure risks. No wonder that even having a doctor’s order for a test may not be enough to get one.

Physician Val Arkoosh, chair of the Montgomery County Board of Commissioners, has urged mildly sick residents who are not elderly, immune-compromised, or otherwise at high risk to stay home and not be tested. “If you could just sit tight and take a deep breath. And I know it’s incredibly frustrating because any of us would want to know for sure,” she said at a news conference. “But in this time of scarce resources, if you are able to sit tight and make a test available for someone who really needs to be tested, that is something that you’re doing for our whole community.”

A test is just a test

Unlike the vaccine that the world hopes to have in a year or so, a diagnostic test is not protective. If you test negative, next week you could still be infected.

“We are not going to test our way out of the crisis, even if we could do all the testing we wanted,” said Wroblewski of the lab association. “It doesn’t prevent a virus from transmitting. It just provides you information on how many people have it and how fast it’s spreading."