Infrared Cameras Can Spot a Fever, but May Not Slow Covid-19


Hildegarde Schell-Chaple, a professor of nursing in charge of screening people entering UCSF’s hospitals, says the available evidence revealed the time and expense of screening with infrared thermometers or cameras was unjustified. “People feel better if they see it happening, but it’s a false sense of security,” she says. “It’s something we should not be doing.” She says CDC documents have been inconsistent on the value of temperature screening; the agency did not respond to a request for comment.

A review of 15 years of previous studies on screening at international borders published last year found checks for fevers or other symptoms, such as a cough, were ineffective at detecting cases during SARS, swine flu, and Ebola outbreaks. ECRI, a nonprofit that studies evidence-based medicine, warned last month that infrared temperature screening is ineffective, even when combined with questionnaires.

Studies, including one presented last year by FDA researchers working on pandemic preparedness, have shown that infrared thermometers and cameras can accurately detect fevers. They use sensors that detect the infrared light, invisible to humans, produced by objects; different wavelengths correspond to different temperatures.

Infrared thermometers, sometimes called noncontact thermometers, and often shaped like ray guns, read the temperature of a single spot on a person’s skin. They are usually aimed at the forehead from a distance of around 6 inches, requiring uncomfortably close contact during pandemic times. Infrared or thermal cameras, like the one in use at King Hospital, produce color-coded images of a whole scene from several feet away showing the temperature of everything in view.

Schell-Chaple, who has done research on fever and body temperature measurement, says there are questions about how reliably the technology performs in everyday health care, a concern shared by ECRI. Accuracy might be even more challenged outside of a hospital or clinic, like at a factory or church.

UCSF’s screening for staff, patients, and others entering its hospitals uses questionnaires that ask people about their health. Schell-Chaple argues that the money and time required to buy and operate infrared temperature screens might be better directed towards other practices aimed at containing coronavirus. Those include using protective equipment and establishing policies for tracing who may have been exposed to an infected patient.

Demand for remote temperature sensors, especially infrared cameras, appears to be growing fast. Companies like Amazon are being accused of lax safety by employees, media, and lawmakers. Checkpoints with shiny new equipment provide a visible, scientific-looking demonstration that safety is being taken seriously.

FLIR Systems, which manufactures its own thermal cameras and sensors used by other companies, saw spikes in sales during SARS, swine flu, and Ebola. The one prompted by the novel coronavirus is the biggest yet, says Chris Bainter, the company’s director for global business development.

In its latest earnings report last week, FLIR said the pandemic had shrunk sales of infrared cameras used on boats, by hunters, and for security, but surging demand for thermal cameras drove revenue 2 percent higher than the same quarter last year. Bainter says the company has prioritized health care providers as it works through a backlog of orders.

The company also sells infrared noncontact thermometers, but it says its FDA-certified cameras, which start at $6,500, are the better option for fever screening. Bainter says the technology can check workers in 10 seconds or less, but that correctly implementing it takes some care and calibration.

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A thermal camera will produce an alluring image of whatever you point it at, color-coded to show the temperature of different objects. But it can’t screen people accurately if they are not properly framed and in focus, Bainter says. FLIR advises that the best readings are obtained from a person’s tear ducts, the inside corner of the eyes, an area well-supplied with blood and less likely than the forehead to be made warm by a hat, hood, or sunlight. FLIR cameras designed for medical use have a “screening mode,” in which the camera flags people significantly warmer than others that day.

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