In recent weeks, a new cadre of gatekeepers armed with thermometer guns has appeared at the entrances of hospitals, office buildings and manufacturing plants to screen out feverish individuals who may carry the coronavirus.
Employees at some companies must report their temperature on apps to get clearance to come in. And when indoor dining resumes at restaurants in New York City later this month, temperature checks will be done at the door.
Since the beginning of the pandemic, the practice of checking for fever has become more and more commonplace, causing a surge in sales of infrared contact-free thermometers and body temperature scanners even as the scientific evidence indicating they are of little value has solidified.
Gov. Andrew M. Cuomo of New York last week called for checking patrons’ temperatures as one of several ground rules for resuming indoor dining in restaurants, along with strict limits on the number of tables and a mask mandate for diners when they are not seated. Restaurants also will be required to obtain contact information from one guest at each table.
There is ample reason for concern. Coronavirus outbreaks — like one in East Lansing, Mich., this summer that infected 187 people — have been traced to superspreading gatherings at bars and restaurants. And a new study by the Centers for Disease Control and Prevention found that one difference between people who contracted the virus and those who did not is that infected individuals were twice as likely to have eaten at a restaurant in the two weeks preceding their illness. The study, however, did not distinguish between outdoor dining and indoor seating, which most experts consider more hazardous.
But while health officials have endorsed masks and social distancing as effective measures for curbing the spread of the coronavirus, some experts scoff at fever checks. Taking temperatures at entry points is nothing more than theater, they say, a gesture that is unlikely to screen out many infected individuals, and one that offers little more than the illusion of safety.
Mr. Cuomo has allowed businesses to demand that patrons undergo temperature checks, and to deny admission to those who refuse or have a fever, and he is requiring restaurants in New York City that resume indoor dining to check customers’ temperatures. The C.D.C. defines a fever as a temperature of 100.4 degrees Fahrenheit or higher; some reports have questioned the accuracy of thermometer guns, however.
While temperature checks may identify people who are seriously ill, those are the people who probably won’t be socializing much or going out for meals. And a growing body of evidence suggests that many of those who are driving transmission are so-called silent carriers — people who have been infected but feel fine, and don’t have a fever or any other symptoms.
Earlier this week, the C.D.C. — which in May told employers to consider checking workers daily for symptoms like fever, but appeared to reverse itself in July — said it would stop requiring airport health screenings beginning Sept. 14 for international passengers from China, Iran, Brazil and other countries because the checks can’t identify silent carriers.
“We now have a better understanding of Covid-19 transmission that indicates symptom-based screening has limited effectiveness because people with Covid-19 may have no symptoms or fever at the time of screening, or only mild symptoms,” the C.D.C. said in a statement.
Temperature checks are akin to “getting the oil checked before you go on a long car trip,” said Dr. David Thomas, an infectious disease specialist at Johns Hopkins University School of Medicine. “It makes you feel better, but it’s not going to keep you from wrecking the car or prevent the tires from falling off. It’s not going to make your trip any safer.”
“It’s something you can do, and it makes you feel like you’re doing something,” he said. “But it won’t catch most people who are spreading Covid.”
Most people who spike a fever feel lousy, and presumably would cancel their dinner plans, said Dr. Thomas McGinn, Northwell Health’s senior vice president and deputy physician in chief. Temperature checks might pick up a few individuals who are unaware of their fever, he said.
But the absence of fever “means nothing,” he said. “It’s not a very sensitive test.”
It does, however, convey a strong public health message, serving as a reminder that people must take precautions, and that itself may be of benefit, Dr. McGinn said. “It makes people think twice, and reminds them that this is a big deal, we still need to be careful, you need someone to stand by the door to do that,” he said.
But here’s the rub: While fever can be a symptom of Covid-19, the disease caused by the coronavirus, not everyone infected with the virus develops a fever, or many other symptoms, for that matter. Physicians writing in the New England Journal of Medicine have called the phenomenon of symptomless spread the “Achilles’ heel of Covid-19 pandemic control.”
Evidence of asymptomatic spread dates back to early in the pandemic, but has been mounting ever since. A recent study from South Korea published in JAMA Internal Medicine in August offered even more proof, finding that infected individuals who don’t feel ill may carry just as much virus in their nose, throat and lungs as those with symptoms — and for almost as long.
A. David Paltiel, a professor of health policy and management at Yale School of Public Health, says these individuals are the “silent spreaders” who are driving transmission and sparking superspreading events.
“You are maximally infectious before you exhibit symptoms, if you exhibit any symptoms at all,” Dr. Paltiel said. “You can be exposed and incubating the virus, and be beginning to shed massive amounts of transmissible virus and be a superspreader, without actually exhibiting any symptoms like a fever.”
Temperature checks will do nothing to stop these “ticking time bombs,” he said. “It’s a bad idea.”
Instead, he said, restaurants should push for access to rapid turnaround, point-of-care tests for patrons.
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Interestingly, even seriously ill coronavirus patients who need medical attention don’t always have a temperature. Of nearly 6,000 patients in the New York area who were so sick last spring that they were admitted to Northwell Health hospitals, only 30 percent were febrile when they came in, according to a study by Dr. McGinn that was published in the Journal of the American Medical Association.
The trend is consistent with earlier reports, including a study from China that looked at more than 1,000 patients admitted to 552 hospitals through the end of January. The study, published in the New England Journal of Medicine, reported that only 44 percent of the patients had an elevated temperature when they were admitted, though most (88 percent) developed a fever during the course of their hospital stay.
In July, the C.D.C. quietly updated its guidance to businesses, acknowledging that symptom and temperature checks “will not be completely effective” because asymptomatic individuals and those with vague symptoms will pass the screenings. But even as the agency warned that “health checks are not a replacement for other protective measures such as social distancing,” it provided detailed guidelines for doing temperature checks, advising the use of disposable or non-contact thermometers and saying screeners should change gloves in between checks.
The bottom line, officials from the federal health agency said, is that screening employees for Covid-19, including using temperatures checks, before they return to work is “an optional strategy businesses can consider implementing depending on their local situation.”
Peter Kuhn, a professor of biological science, medicine and engineering at the University of Southern California, said his studies suggested that fever is often a first symptom of the coronavirus. And while temperature checks may be useful, he said they should be used in conjunction with a comprehensive package of safety measures that include requiring masks and social distancing, and ensuring good ventilation and access to a flow of fresh air.
“Temperature checks are one part of that, but they are only one part,” Dr. Kuhn said. “If anyone would argue that they can provide complete safety for indoor dining, that is completely wrong. It’s not a magic bullet.”