Non-contact thermometers alone are insufficient for detecting Covid-19, researchers warn

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  • Fever is the most common symptom associated with Covid-19 infection
  • Many organisations are making use of non-contact infrared thermometers as a diagnostic tool
  • However, researchers found that taking temperature falls short as a screening tool

Most of us have been subjected to a pistol-shaped device aimed at our foreheads in order to determine if we will be allowed access to a building or not.

Many businesses have invested in these devices – known as non-contact infrared thermometers (NCITS) – because one of the most common symptoms of Covid-19 is fever, and testing body temperature is regarded a good precautionary method.

However, researchers at the Johns Hopkins Medicine and the University of Maryland School of Medicine have concluded that merely taking a person’s body temperature is a poor means of testing whether they have the virus or are contagious. The editorial containing these findings was published in the journal Open Forum Infectious Diseases.

There is no 'body temperature'

According to South African guidelines for Covid-19 monitoring, a fever is defined as a body temperature of 38°C or higher. However, in the editorial researchers expressed that it is hard to define "body temperature". 

“Because temperature varies throughout the body by anatomic site, the term 'body temperature' is meaningless. There is an axillary temperature, an oral temperature, a rectal temperature and so on, all of which differ.

"In general, axillary temperatures are slightly lower than simultaneously obtained oral temperatures, which are lower than rectal temperatures. In the face of such variability, there is no 'body temperature', only the temperatures of individual body parts,” the researchers explained. 

They went on to say that "core temperature" is the closest one would get to actual body temperature, as it refers to the temperature of blood in the veins. The problem with reading core temperature is that it is much more invasive than NCITs and would not be practical considering physical distancing.

NCIT readings questionable

NCITs are not reliable because they measure surface temperature which can be influenced by a range of factors such as “the subject’s age and gender and medications” and “women have slightly higher temperatures than men”. 

New screening methods are needed

As many as 45% of individuals infected with the virus are asymptomatic, meaning that any method of screening, other than a test for the virus, would be ineffective. The researchers suggested strategies other than NCITs screening must be developed to distinguish those who are infected from those who are not.

Authors William Wright and Philip Mackowiak explained: “Because mass screening for the virus is constrained by our current capacity to do so and the cost of such a programme, should it become available, innovative tactics for public health surveillance, such as those involving group testing, crowdsourcing of digital wearable data, geolocated fever measurements from 'smart thermometers' (i.e., thermometers paired to mobile devices) and monitoring sewage sludge for SARS-CoV-2 are worth considering."

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