Temperature Scanners Unreliable in Detecting Fever

February 12, 2021

New research shows that no-contact forehead thermometers used worldwide to screen for fever in public places are unreliable in detecting fever and of limited value in detecting covid.

A pair of European researchers – an expert in temperature regulation and a human physiologist – estimating the validity of infrared thermography (IRT) forehead scanners which are used worldwide to screen for fever in public places found that they are unreliable and of limited value in detecting covid.

The new paper – entitled, “Myths and methodologies: Degrees of freedom – limitations of infrared thermographic screening for covid‐19 and other infections” and published in “Experimental Physiology” (a publication of “The Physiological Society”) – questioning no-contact forehead thermometers shows that they can result in false negatives and false positives.

The human body maintains an internal temperature that varies slightly throughout the day, depending on physical activity, emotional state or foods. On the contrary, a remarkable change in core body temperature can happen during an illness or an infection: an early sign of infection is a fever or an increase in core temperature that human body uses to fight pathogens.

The variability in skin temperature, yet, is independent of core body temperature. Differences in skin temperature could be due to a wide range of reasons, including whether the individual has recently exercised, has an infection, sunburn or recently drunk alcohol, how close an individual stands to a scanner, how warm or cool the air is, how much fat a person has on their body and even their blood pressure. Authors explain that, while fever is a common symptom of covid-19, making people stand in front of a forehead scanner to have their core body temperature read can result in a large number of false negatives, allowing people with covid-19 to pass through airports and hospitals undetected.

They also point out that a change in deep body temperature is a critical factor in diagnosing a potential disease, but the many methods of detecting deep body temperature, widely used in hospitals, are too expensive, invasive and time consuming to be widely used outside hospitals.

The study found four key factors: 

1) Temperature alone isn’t a good indicator of disease – not all who have the virus have a fever and many who do, develop one only after admission to hospital; 

2) Measuring skin temperature doesn’t give an accurate estimation of deep body temperature (raised in a fever). A direct measure of deep body temperature is impractical; 

3) A high temperature, even one taken from deep body, does not necessarily mean a person has Covid-19; and 

4) Taking two temperature measurements, one of the finger, the other of the eye, is likely to be a better and more reliable indicator of a fever-induced increase in deep body temperature. 

No-contact forehead IRT thermometers, researchers says, can easily be adapted to take these two measurements. They also argue that taking temperature readings of a person’s fingertip and eye would give a significantly better and more reliable reading and help identify those with fever.  

Mike Tipton, co-author of the paper and expert in temperature regulation, stated: “If scanners are not giving an accurate reading, we run the risk of falsely excluding people from places they may want, or need, to go, and we also risk allowing people with the virus to spread the undetected infection they have.” 

“Using a surface temperature scanner to obtain a single surface temperature, usually the forehead, is an unreliable method to detect the fever associated with covid-19. Too many factors make the measurement of a skin temperature a poor surrogate for deep body temperature; skin temperature can change independently of deep body temperature for lots of reasons. Even if such a single measure did reflect deep body temperature reliably, other things, such as exercise can raise deep body temperature.”

Tipton concluded: “During the SARS epidemic, in 2003, there was a need for a fast, effective mass screening method and infrared thermography became and remains the cornerstone measurement, despite concerns over its reliability. It’s critical we develop a method of gauging if an individual has a fever that’s accurate and fast. We think we can improve the identification of the presence of fever using the same kit but looking at the difference between eye and finger temperature – it’s not perfect, but it is potentially better and more reliable.”

Full Study “Myths and methodologies: Degrees of freedom – limitations of infrared thermographic screening for Covid‐19 and other infections”
Article by The Physiological Society “Temperature scanners of limited value in detecting Covid-19”