If you think you have the flu, you go to the doctor’s office and get a test. Within minutes, there are very accurate results that tell you whether you have the flu or not.
If you think you might have the coronavirus, you go to the doctor’s office. Even if there were plenty of test kits, the current time frame to get results is 3 to 5 days. And the test itself is only about 70 percent accurate.
The difference comes down to a metric known as sensitivity of the test: how many people who have the virus will indeed test positive. No medical test is perfect. Some are too sensitive, meaning that the result may say you’re infected when you’re actually not. Others aren’t sensitive enough, meaning they don’t detect something that is actually there.
The latter is the model for a diagnostic test. These tests can help to confirm that a sick person has the virus; but they can’t always tell you that a person does not. When people come into a clinic or hospital with severe flu-like symptoms, a positive test for the new coronavirus can seal the diagnosis. Screening mildly ill people for the presence of the virus is, however, a different challenge.
Results can take anywhere from 24 hours to 3-5 days, which means that figures on the number of infections could reflect what the situation was three days ago, not what it is today. And as we’ve seen in Italy, three days can make the difference between an outbreak and a pandemic.
“An inaccurate test—one prone to false positive or false negative results, can be worse than no test at all,” Ian Lipkin, an epidemiology professor at Columbia University, told me in an email. The CDC has not shared the exact sensitivity of the testing process it has been using. When Fauci was asked about it on Monday, he once again hedged. “If it’s positive, you absolutely can make a decision,” he said. If it’s not, that’s a judgment call. Usually a second test is recommended, and it depends on the patient’s symptoms, exposures, and how sick they appear to be.But if tests aren’t highly accurate, the consequences can be as bad as the coronavirus itself.
There are plans in the works to come up with a test where results would be found in minutes. But it’s at least months away.
Given the number of variables, widespread screening tests for the virus are not looming on the horizon as a way to obviate the urgent need for social distancing.
Some hope is being placed in biotech companies that are working to develop quick, mobile tests that could give results anywhere—be it at a doctor’s office or in a modified parking lot. “The goal would be to allow people to know if they have a cold or if they have the virus and need to self-quarantine, right there in the doctor’s office,” says William Brody, a radiologist and former president of Johns Hopkins University. He is currently working on one such project with Hong Cai, a molecular biologist, at a small company called Mesa. The duo told me this is, at best, months away from being tested widely. Even then, its sensitivity will remain to be seen, and will likely be less than that of the current, slower tests. But Hong says her team is working as expeditiously as possible to solve the problem.
“Social distancing.” You’ll be hearing that a lot in the very near future. And it depends on accurate, quick testing. If someone has been exposed and gets a negative test result, they should be able to go back to work and carry on with their daily lives. Those who test positive can be immediately quarantined, thus preventing the spread of the disease.
But in the absence of accurate, immediate testing, everybody has to be quarantined. It’s the difference between an economic slowdown and a severe recession. Most companies can operate with skeleton staffs. But closing the office means layoffs or firings, starting an economic chain-reaction that could lead to supply disruptions, and even mass business failures.
But the current testing regime is what we’ve got and we have to get better at being able to test more people and test them faster.
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