Temperature checks are becoming a normal part of life in many places across the country, from your local gym to Disneyland, where, if your temperature is above 100.4 degrees Fahrenheit, you won’t get in. The Centers for Disease Control and Prevention (CDC) has even recommended that all businesses might check employee temperatures daily. But scientists say that this practice isn’t rooted in science—and might actually help COVID-19 keep spreading.
“There’s never been any data to show that it’s prevented any transmissions [of COVID-19],” says Eric Topol, executive vice president of Scripps Research. “The temperature check is of no value. It should be abandoned.”
The idea of using temperature checks to filter out sick people dates back to the SARS epidemic of the early 2000s. Their exact usefulness in containing SARS is still debated, but temperature was indeed a fairly reliable indicator of a SARS infection, with at least 86 percent of those infected showing a fever, reports Helen Branswell for Stat.
“Temperature checks are cheap, easy and quick to perform, and did quite well screening for SARS 1 in 2002 / 2003,” Mara Aspinall, an Arizona State University professor of biomedical diagnostics, told Popular Science by email. Aspinall is also the CEO of a biotechnology research and consulting firm.
But SARS-CoV-2, the virus that causes COVID-19, has key differences “that make temperature checks almost useless this time around,” she writes. For one, current data suggests that fewer than half of people who have COVID-19 ever develop a fever. Even those people who will eventually exhibit symptoms are often contagious before their temperature spikes.
In fact, the group of people most likely to be asymptomatic spreaders of the virus (young people) and those most vulnerable to the virus (over-65s and immunocompromised individuals) are unlikely to present with fevers at all, although for very different reasons.
Young people are more likely to just not show any signs of illness at all, while the other group may not be healthy enough. “You actually have to be kind of healthy to mount a fever,” says Andrew Morris, a professor of medicine at the University of Toronto and a working doctor at Toronto’s Mount Sinai Health System.
Beyond that, Aspinall writes, “there are many other illnesses that do present with fever, making this an ineffective screening test particularly during flu season that begins in the fall in the US.”
“A measure that’s neither sensitive nor specific is not a very good measure,” he says. “It may also give people a false sense of security.” Even if someone has COVID and is running a fever, he says, they can probably temporarily reduce it using a drug like Tylenol to get past screening. In other words: temperature checks won’t help, and they may hurt.