Non-contact thermometers fall short as COVID-19 screeners, experts say

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Taking one's temperature is a poor means of screening who is infected with SARS-CoV-2, the virus that causes the novel coronavirus (COVID-19), and, more importantly, who might be contagious, according to a new perspective editorial by researchers at Johns Hopkins Medicine and the University of Maryland School of Medicine published in the journal Open Forum Infectious Diseases.

The editorial, authored by William Wright, DO, MPH, assistant professor of medicine at the Johns Hopkins University School of Medicine, and Philip Mackowiak, MD, MBA, emeritus professor of medicine at the University of Maryland School of Medicine. describes why temperature screening, primarily done with a non-contact infrared thermometer (NCIT), doesn't work as an effective strategy for stemming the spread of COVID-19.

In March 2020, the U.S. Department of Health and Human Services (HHS) and the U.S. Centers for Disease Control and Prevention (CDC) released guidelines for Americans to determine if they needed to seek medical attention for symptoms suggestive of infection with SARS-CoV-2, with temperature screening playing an integral role. According to the guidelines, fever is defined as a temperature, taken with an NCIT near the forehead, of greater than or equal to 100.4 degrees Fahrenheit (38.0 degrees Celsius) for non-healthcare settings and greater than or equal to 100.0 degrees Fahrenheit (37.8 degrees Celsius) for healthcare ones.

In the editorial, the authors provide statistics to show that NCIT fails as a screening test for SARS-CoV-2 infection. As of February 23, 2020, more than 46,000 travelers were screened with NCITs at U.S. airports, and only one person was identified as having SARS-CoV-2, they said. In a second example, CDC staff and U.S. customs officials screened approximately 268,000 travelers through April 21, 2020, finding only 14 people with the virus.

From a November 2020 CDC report, the authors provide further support for their concern about temperature screenings for COVID-19. The report, they say, states that among approximately 766,000 travelers screened during the period January 17, 2020 to September 13, 2020, only one person per 85,000, or about 0.001 percent, later tested positive for SARS-CoV-2. Additionally, only 47 out of 278 people (17 percent) in that group with symptoms similar to SARS-CoV-2 had a measured temperature meeting the CDC criteria for fever.

Another problem with NCITs, the authors said, is that they may give misleading readings throughout the course of a fever that make it difficult to determine when someone is actually feverish or not.

Overall, the authors conclude that these and other factors affecting thermal screening with NCITs must be addressed to develop better programs for distinguishing people infected with SARS-CoV-2 from those who are not. Among the strategies for improvement that they suggest are lowering the cutoff temperature used to identify symptomatic infected people, especially when screening those who are elderly or immunocompromised; group testing to enable real-time surveillance and monitoring of the virus in a more manageable situation; "smart" thermometers or wearable thermometers paired with GPS devices such as smartphones; and monitoring sewage sludge for SARS-CoV-2.

"Readings obtained with NCITs are influenced by numerous human, environmental, and equipment variables, all of which can affect their accuracy, reproducibility and relationship with the measure closest to what could be called the body temperature, the core temperature, or the temperature of blood in the pulmonary vein," said Wright in a statement. "However, the only way to reliably take the core temperature requires catherization of the pulmonary artery, which is neither safe nor practical as a screening test.”

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