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COVID-19 symptoms: Fever screening widely used for schools, businesses. Is it reliable?

A temperature check only detects people who are showing symptoms.
Image: Hollywood High School Students And Teachers Prepare For Coming School Year
Aracelia Gasper Andres performs a contactless temperature check at Hollywood High School in Los Angeles on Aug. 13.Rodin Eckenroth / Getty Images

Fever checks have widely become the first level of coronavirus detection as businesses, stores and schools try to reopen, but experts caution that relying on them as a single screening tool could lead to a false sense of security.

Fever is generally the first symptom of a coronavirus infection, according to a study from the University of Southern California, followed by cough, nausea, vomiting and lower gastrointestinal symptoms, such as diarrhea.

For the study, researchers used World Health Organization data, which included information on nearly 60,000 confirmed cases of COVID-19, to model the order of symptoms. Limitations of the study, published last week in a public health journal, include that the cases were almost all from China during the early days of the pandemic, before other types of symptoms were recognized.

While a temperature check can detect people who are showing symptoms, there are a significant number of people who could be contagious that don't develop a fever, said study co-author Peter Kuhn, a professor of biological sciences, medicine and engineering at USC.

A temperature of 100.4 F is considered a fever by the Centers for Disease Control and Prevention.

With more than 21 million confirmed COVID-19 cases worldwide, public health officials have learned that the infection can cause a wide range of symptoms, from barely noticeable sniffles and headaches to difficulty breathing and chest pain. The CDC currently lists the following possible symptoms, but says there may be others:

  • Fever or chills
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue
  • Muscle or body aches
  • Headache
  • New loss of taste or smell
  • Sore throat
  • Congestion or runny nose
  • Nausea or vomiting
  • Diarrhea

Studies have shown that children are more likely to have milder symptoms, which could be mistaken for a different illness. A new loss of smell and taste is a common early symptom for milder cases, and is more common among younger patients and women.

Symptoms can appear anytime between two to 14 days, although about five to six days after exposure is the average. While many people never show signs of infection, even those who eventually do become symptomatic could spread the disease for days prior to developing a fever, said David Paltiel, a professor at the Yale School of Public Health.

“If you’re using signs and symptoms as a basis for moving ahead, it’s like the fire department waiting until a house has burned down before springing into action,” said Paltiel, who published a study in July on bringing college students back to campus in JAMA Network Open.

At the UPMC Magee-Womens Hospital in Pittsburgh, all visitors are screened with temperature scanners, said Dr. Joe Suyama, chief of emergency services.

“They are not the technological safety net that most people expect them to be,” he said. “However, most institutions, hospitals and schools are implementing some form of screening.”

Suyama and others hope that, along with blocking entry to people with symptoms, the screening stations will remind people that no one can let their guard down. Fever checks need to be a part of other protocols that include masks and social distancing, infectious disease experts say.

“Because screening for the virus is so imperfect, it’s better not to count on it,” said Dr. David Thomas, a professor of medicine and director of the division of infectious diseases at Johns Hopkins Medicine. “It’s not that we don’t believe in testing and screening, but we don’t trust them entirely.”