Fever screens seem part of America’s ongoing failure to learn an abiding lesson of modern medicine: Screening tests often backfire. They have value only in specific contexts. Doctors have repeatedly seen this play out with lifesaving tests like mammograms, CT scans, and colonoscopies, which can lead to unnecessary biopsies and surgeries when overused.
Body temperature is a vital sign that is monitored continually in hospitals, where it can be an invaluable window into how a patient is faring. But screening groups of people for the coronavirus is a different matter, and that is what’s happening now. Employers around the United States are attempting to order daily temperature checks to determine who is allowed to enter an office and do their job. As you noticed, access to courts may be based on this test. Fever screens have even been implicated in many plans to open schools: New York City’s Department of Education announced last week that kids would be randomly screened before being allowed to enter school buildings, despite the fact that kids with the virus rarely develop fevers.
Read: Hygiene theater is a huge waste of time
Temperature checks were first deployed in January amid China’s “throw everything at the wall and show the world we’ve got this locked down” attempt to stop the virus. News reports showed people being ordered out of their car at tollbooths to have infrared thermometer guns placed against their forehead. For a period in February, the Chinese government required some 11 million people to report temperatures to the government daily. By late February, though, researchers had begun reporting that the tactic wasn’t an effective screening tool for this new disease. Unlike Ebola and some other infectious diseases, this coronavirus is contagious before symptoms appear. Many infected people never develop any symptoms at all. While a fever is one of the most common symptoms for people who do get sick, it’s still far from universal among those infected. In June, a study at an Australian hospital found that a minority of patients admitted with the virus had a fever. The researchers concluded that “using fever as a screening tool for COVID-19 may provide a false sense of security.”
But what’s the harm? In this moment, that’s a question we need to take seriously—with regard to tests, hygiene practices, or anything else we might be doing to try to stay safe. Anything with the potential to benefit our health also has the potential to undermine it. If people are reassured by a fever check and compromise on the basics—wearing a mask, distancing, hand-washing—they put themselves and others at risk. This test has no ability to reassure people, but a real ability to mislead.
A useful test is both sensitive and specific. If you haven’t encountered these terms yet, they can seem esoteric, but we should all know them. A test is considered sensitive if it catches most (and ideally all) cases. A test is specific if it doesn’t misidentify too many cases—that is, if it doesn’t catch too many more than all.