Science

MailOnline puts seven thermometers to the test

Non-contact infrared thermometers are commonly used in workplaces and restaurants as a screening tool for Covid-19, but a recent article by two leading experts have questioned the validity of these temperature checks.  

Dr William Wright at the Johns Hopkins University and Dr Philip Mackowiak, Emeritus professor of medicine at the University of Maryland, say the devices are inaccurate, unreliable and ‘lull people into a false sense of security’.

MailOnline looked at seven thermometers available on the market to test their accuracy, and found that readings for a single healthy individual ranged from 36.2°C to 37.6°C.  

A reading greater than or equal to 100.4F (38°C) is considered a fever when taken outside of a healthcare environment.

However, Dr Mackowiak told MailOnline the true reading for body temperature can only be obtained via a highly invasive procedure which inserts a thermometer into the pulmonary artery via a catheter. These are reserved solely for seriously ill hospital patients. 

He says a rectal thermometer is the next best way to get an accurate temperature reading, but practical limitations make it unsuitable as a screening mechanism, so suggests that an oral reading is the best option.  

‘There are several reasonable ways to take temperature, an oral thermometer is probably the most reliable and practical under usual circumstances but would not be practical in massive screening applications, especially when you’re concerned with a highly infectious pathogen such as Covid-19,’ he said. 

‘Thermal screening and thermometers provide a false sense of security,’ Dr  Mackowiak adds. ‘The alternative is to focus on social distancing and the use of masks and not fool yourself into believing cases can be spotted by using thermal screening as it just is not going to work.’

Here, MailOnline assesses the instruments and methods to see which, if any, should be employed on a larger scale. All tests were done at the same time on the same tester. 

Non-contact infrared thermometers are commonly used in workplaces and restaurants as a screening tool for Covid-19, but a recent article by two leading experts have questioned the validity of these temperature checks (stock photo)

Rectal thermometer – 37.6°C

Given the advice of the experts, MailOnline used the internal core body temperature measurement from a rectal probe as the baseline, or ‘gold standard’ for the most accurate reading.  

A slimline digi-T-40F thermometer with a flexible tip was purchased brand new for £5 which gives results in 40 seconds. The result was 37.6°C

Although this approach provides the best hypothetical option for spotting any sign of fever, its invasive nature and the high contamination risk means it is ruled out for various logistical reasons.

‘In relation to core temperature, a rectal thermometer has the closest relationship [to a person’s actual core temperature],’ Dr Mackowiak says. 

Oral gallium and digital  thermometer  and armpit measurement – 36.2°C/36.3°C/36.6°C

Dr Mackowiak explains that an oral thermometer is likely to give the best results, after rectal has been ruled out. 

This is due to the fact it sits under the tongue and is therefore protected from some external factors which may alter the reading. 

However, the mouth is naturally cooler than the rectum, which causes the accepted range of temperatures to shift down. 

According to the University of Michigan, oral temperature is, as a general rule of thumb, around 0.3 – 0.6°C lower than rectal temperature.  

A traditional-type thermometer from a local pharmacy for £5.35 which uses gallium was used which takes four minutes to give an accurate result, and gave a reading of 36.2°C in the MailOnline test. 

A £12 digital thermometer (Boots own brand) gave a similar reading of 36.3°C

Both these figures are within the accepted range for a healthy individual. While the 0.1°C may seem negligible, it is testament to the lack of reliability exhibited by these thermometers. 

Reliability is defined by the ability for several results to be close to the same value, even if this value is some way from the true value. 

Armpit 

Using the same digital probe as the oral test — after it had been suitably sanitised by the attending qualified healthcare assistant helping with the investigation — the axillary (armpit) result was 36.6°C

This aligns closely with the oral findings, as Dr Mackowiak predicted.

‘Armpit temperatures are probably next in line [after oral and rectal] although they can vary due to the impact of external environmental conditions,’ he said. 

‘Last on the list is skin tests, which are most affected by external factors.’ 

A traditional-type thermometer which uses gallium instead of mercury (pictured) takes four minutes to give an accurate result gave a reading of 36.2°C in the MailOnline test. A digital thermometer (Boots own brand) gave a similar reading of 36.3°C

Armpit temperatures are probably next in line [after oral and rectal] although they can vary due to the impact of external environmental conditions,' Dr Mackowiak said

A traditional-type thermometer which uses gallium instead of mercury (pictured) takes four minutes to give an accurate result gave a reading of 36.2°C in the MailOnline test. A digital thermometer (Boots own brand) gave a similar reading of 36.3°C

Forehead scanning gun – 36.2°C

Non-contact thermometers are particularly appealing to physicians and the general public, because they minimise the chances of transmitting the virus via direct contact, Dr Mackowiak told MailOnline. 

However, their effectiveness is yet to be fully determined as little research has looked at their accuracy and reliability. 

In their editorial article, Dr Mackowiak and Dr Wright cited one study, in which approximately 268,000 travellers were screened for Covid-19 using infrared forehead-scanning guns at an airport in the US. 

Only 14 of these individuals were found to have the virus as a result of the scans. 

The gun takes the temperature of the skin on the face, and this can often vary, with external environmental factors affecting the reading, they explained. 

For example, cold or hot weather and recent physical exertion can lead to an erroneous result. 

In the MailOnline test, a reading of 36.2°C was recorded. This finding aligns with the oral results, but the issue, Dr Mackowiak explains, is the replicability of the results. 

They may give a figure in the right range, but they will rarely give the same reading twice. This severely jeopardises their effectiveness and the confidence clinicians can have in their readings.  

'Using non-contact thermometers has been so appealing to physicians and the general public alike because the chance of transmitting the virus via direct contact is minimised,' Dr Mackowiak told MailOnline. In the MailOnline test, a reading of 36.2°C was recorded, the same as the oral test

‘Using non-contact thermometers has been so appealing to physicians and the general public alike because the chance of transmitting the virus via direct contact is minimised,’ Dr Mackowiak told MailOnline. In the MailOnline test, a reading of 36.2°C was recorded, the same as the oral test

Xenon AI-powered ‘Fever Defense’ machines – 36.5°C 

Pictured, the Xenon Fever Defence £2,000 tool which uses AI and IR sensors to determine a person's temperature

Pictured, the Xenon Fever Defence £2,000 tool which uses AI and IR sensors to determine a person’s temperature 

A standalone, automated face scanner which determines a person’s body temperature from several feet away has been built by a company called Xenon Fever Defence.  

This £2,000 piece of equipment rapidly scans a person’s face, determines their temperature and then flashes green if it is within the predetermined range, or red if it is too high, indicating a person may also have a fever. 

It also provides a specific figure for temperature, using a combination of infrared scanners and artificial intelligence.

The machine is calibrated to function best at a specific distance, but as it relies on users positioning themselves, it introduces another factor which makes it less reliable than other options. 

The company manufacturing it claims it is accurate within plus or minus 0.3°C, a significant range.  

In the single MailOnline test it read 36.5°C.    

Forehead scanning tool – skin-to-device contact – 37.1°C

A brand new Sejoy infrared forehead thermometer, which can be bought off the shelf at several high street retailers for around £50, was tested at the same time as all the other thermometers.

This requires direct contact with the person being scanned, and is therefore not as Covid-safe as the previous gadget. However, it could be wiped clean and sterilised relatively easily.

It gave a reading of 37.1°C during the MailOnline test – much warmer than the similar device that does not come into contact with the person’s face.

The academics say using skin temperature to gauge fever is unreliable and highly variable, with each reading likely to be different. 

A brand new Sejoy infrared forehead thermometer, which can be bought off the shelf at several high street retailers for around £50, was tested at the same time as all the other thermometers (pictured)

A brand new Sejoy infrared forehead thermometer, which can be bought off the shelf at several high street retailers for around £50, was tested at the same time as all the other thermometers (pictured)

In-ear infrared digital thermometer – 36.8°C

A Boots own-brand ear thermometer (£30), which is suitable for anyone over the age of six months was also trialled. 

It yielded a reading of 36.8°C, warmer than the oral, armpit, and non-contact gun but cooler than the rectal value. This places it somewhere in the middle for its accuracy, but researchers still question its reliability. 

‘In-ear infrared thermometers are commonly used in surgeries, outpatient settings and clinics but have fallen out of favour as they involve direct contact. They also tend to be variable in their reliability,’ Dr Mackowiak explains. 

‘If you take the temperature of one ear and then take the opposite ear, they tend to be different and this is a perfect example of their unreliability.’

In-ear infrared thermometers (pictured) are commonly used in surgeries, outpatient settings and clinics but have fallen out of favour as they involve direct contact. They also tend to be variable in their reliability

In-ear infrared thermometers (pictured) are commonly used in surgeries, outpatient settings and clinics but have fallen out of favour as they involve direct contact. They also tend to be variable in their reliability

So can you trust any of them?

The thermometers performed pretty much as expected throughout the test, but this highlights their fundamental flaws. 

The most accurate detection methods are also the most impractical – particularly in situations where they are most needed, such as entering restaurants or schools – due to their invasiveness and the need to sterilise them between uses.

This leaves only a handful of available options, but the experts insist that non-contact thermal scanners give people a false sense of security, making people believe they are safe when in fact this is far from true.  

‘There is no easy way to identify Covid infected patients. Taking temperatures, particularly if you are in a position to use a reliable thermometer, which is difficult with transmissibility even if they worked perfectly, would only be effective at identifying about half of all cases,’ said Dr Mackowiak. 

‘Half are asymptomatic and therefore not only have no fever but show no symptoms at all. If you was hellbent on identifying all the cases you would have to do surveys and mass testing, which in itself is a logistical nightmare.’ 

Instead, it may be best to accept that digital temperature screening is a fool’s errand, and instead focus on other interventions which can stop the spread of Covid-19, such as strict hand washing, social distancing and wearing a mask.


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