Eyeball and fingertip temperature checks are ‘much more reliable’ than body scans at detecting fevers associated with COVID-19, scientists claim


Thermal screening to spot people infected with coronavirus is more reliable when scanning the eyeball and fingertip than taking body or forehead measurements. 

Experts in human physiology published a scientific article on the usefulness of thermometers which scan a person’s skin to detect a fever. 

They say the current process is fundamentally flawed and produces a large number of false negatives, as well as some false positives, and also because not all people infected with the coronavirus develop a fever.

A fever is defined as a temperature of greater than or equal to 100.4F (38°C) if spotted outside of a healthcare environment.

In healthcare settings, such as a hospital, a fever is technically defined as anything greater than or equal to 100.0F (37.8°C).

Forehead-scanning thermometers have become ubiquitous as a way of detecting a fever, the most common symptom of coronavirus infection.

Instead of using thermal techno-logy on the forehead to gauge body temperature, the researchers say adapting the apparatus to get temperatures from the fingertip and eye would be a quick fix that has drastic improvements to reliability. 

Professor Mike Tipton from the University of Portsmouth, co-author of the research published in the journal Experimental Physiology, points to four major issues with the current scanners.

Detecting an elevated body tem-perature itself is an unreliable indi-cator of coronavirus infection, as at least 11 percent of those with COVID-19 do not have a fever, they say. This drops to less than half for people with COVID admitted to hospital.

Also, the researchers point out, if a person does produce a high body temperature, this is not a guarantee they have COVID-19, as it could be the result of another infection, the weather, recent exertion or consumption of alcohol, for example.

As well issues with the fever as a symptom, the non-contact infrared gadgets being employed also do not give an accurate measure of ‘deep’ body temperature.

To get a true gauge of a person’s internal body temperature a catheter is the best possible technique, with rectal thermometers the next best substitute.

This, the researchers say, is impractical as a COVID-19 scree-ning method as it is highly-invasive and time-consuming. Also, taking a single measurement is always fraught with reliability issues, and taking two measurements from different parts of the body would instead be better, the new study states.

For example, using retinal tem-peratures in conjunction with mea-surements taken from the fingertip would be a more robust method, the academics advise.Professor Tipton said: ‘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.

‘The pandemic has had a devasta-ting global effect on all aspects of our lives, and unfortunately, it’s unlikely to be the last pandemic we face.‘It’s critical we develop a method of gauging if an individual has a fever that’s accurate and fast.’

The researchers looked through the vast reems of research now available  on  the  symptoms  of COVID-19 in patients and found that in a February 2020 study from China, fever was the most common symptom of 55,924 confirmed COVID-19 cases.

But one in ten did not have a fever and people were infectious several data before they developed a fever. These individuals would therefore have a window where they would pass thermal screening while spreading the virus to others.

A recent MailOnline investiga-tion found thermal-scanning devices registering temperatures up to 1.4°C (2.5°F) lower than recommended methods. Mail Online tested seven thermo-meters and obtained readings for the same healthy person which ranged from 36.2°C to 37.6°C. The infrared readings were the farthest from the measure considered most reliable by experts.

A reading greater than or equal to 38°C (100.4F) is considered a fever when taken outside of a healthcare environment, and a high temperature is cited by the NHS as one of the main symptoms of coronavirus.

In an opinion piece published in December, Dr William Wright at the Johns Hopkins University and Dr Philip Mackowiak, Emeritus professor of medicine at the Univer-sity of Maryland, criticised the use of thermal screening and said the devices ‘lull people into a false sense of security’.

Dr Mackowiak told Mail Online the true reading for body temperature can only be obtained via a highly invasive procedure, reserved solely for seriously ill hospital patients, which inserts a thermometer into the pulmonary artery via a catheter. He said a rectal thermometer was the next most accurate method, but its obvious practical limitations make it unsuitable for screening. He suggested an oral reading is the most accurate option.

But, again, it ‘would not be pra-ctical in massive screening appli-cations, especially when you’re concerned with a highly infectious pathogen such as COVID-19’. Experts slam the use of infrared forehead-scanning thermometers Leading doctors have warned against the use of infrared thermo-meters that scan a person’s forehead to check for coronavirus infection.

Such technology was widely deployed by shops, restaurants and workplaces as a form of screening to spot signs of fever, one of the main symptoms of COVID-19. But Dr William Wright at the Johns Hopkins University and Dr Philip Mackowiak, Emeritus, professor of medicine at the Uni-versity  of  Maryland  School  of Medicine, have questioned their accuracy, and rubbished claims the devices are an effective tool in preventing the spread of COVID-19.

‘Readings obtained with non-contact infrared thermometer 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,’ says Dr Wright.

‘However, the only way to reliably take the core temperature requires catheterisation of the pulmonary artery, which is neither safe nor practical as a screening test.’