Infrared thermometers: are they useful or not?

The thermometer is an essential part of the first aid kit, but its infrared variable, shaped like a gun, is being one of the most used in monitoring people in massive places. Will it be necessary to have it at home? Three experts give their verdict.

For months we have been being gunned down by thermometers. Streets, roads, shopping centers, supermarkets and airports are some of the spaces where you have probably been controlled by a health official, guard or inspector, pointing directly at your body.

At first, many became nervous, especially when the thermometer gun could not calculate the temperature, and therefore they aimed elsewhere, such as the neck or wrist. Today, that shot is one more of the routine measures in this new “normal” scenario.

But just as they measure our temperature before entering almost any public place, will it be necessary for us to do the same with those who visit us? Is it essential to have a thermometer at home? Three health experts respond.

Types of thermometers

The first thing you need to know is that there are different types of thermometers.

Mercury thermometer

This is the one that most have in their medicine cabinet. “Its accuracy and precision are characterized by being superior to others,” comments nurse Carolina Calderón, from the Clínica Alemana. Its weak point is that it can break easily, “and since the mercury evaporates, it can be a risk for the body,” says the professional.

This thermometer must be disinfected after each use, and the temperature of the device must be lowered manually. Another of its characteristics, not very comfortable for everyone, is that “the shooting result is not very visible,” adds Calderón, and it can take between 4 to 5 minutes to be noticed.

Ignacio Silva, infectious disease specialist and academic in the postgraduate department of the Faculty of Medical Sciences of the University of Santiago adds that, although they are “precise”, they are no longer “so recommended due to the risk of poisoning.”

Digital thermometer

This is a kind of upgrade of the traditional mercury thermometer, since its digital cousin works through "a metal detector at the tip, which heats up upon contact with the skin of the body, giving us the reading after a few minutes on a digital screen", Carolina Calderón specifies.

Regarding its effectiveness, this model can occasionally fail, “it can vary by up to two degrees with the actual body temperature,” the nurse details. This small device must also be disinfected before and after use, and although they have this margin of error, they are considered “reliable and cheap.”

“This thermometer is a contact thermometer, and it works in the same way as a mercury thermometer: it can be placed under the armpit, inside the oral or rectal cavity,” points out Ignacio Silva.

Non-contact digital thermometer (or infrared)

This is the type of thermometer that we are encountering in various public places. They are devices that “measure temperature through infrared energy,” explains Carolina Calderón.

“They have a precision of +/- 0.2,” adds the nurse, and their measurement distance varies between 5 to 10 centimeters.

How can you measure temperature without touching? This magic, which is actually science, is due to a lens that is located centimeters from the forehead. "The explanation is that the human body, just like objects, give off infrared rays with various wavelengths depending on the heat, and the thermometer lens converts these radiations into electrical signals that then, under a complex mechanism, are interpreted and converted. in a digital signal to know the body temperature,” explains Calderón.

This type of device “has the advantage that, by not having physical contact, it prevents the thermometer from being contaminated,” says Ignacio Silva. Their main disadvantage is “that they are less precise”, a factor that according to the infectious disease specialist would be “related to the price”.

In times of covid-19, you cannot depend on the thermometer

Although the infrared thermometer is the most hygienic among its peers, since it does not require direct contact to obtain results, it has some cons that are necessary to know, especially if someone is thinking of investing in one of these devices.

It is common knowledge that fever is one of the symptoms of covid-19, however, it is not the only one. “According to the statistics of coronavirus patients, 70% have fever at the beginning of the infection,” explains bronchopulmonary doctor Jorge Jorquera. The remaining percentage is the one that is worrying, because they may be asymptomatic cases.

“Non-contact temperature assessment devices are not effective if used as the only means to detect a Covid-19 infection,” adds Carolina Calderón. Within the scientific literature it has been identified that the effectiveness of this device may be limited by several factors, such as "infections without fever, the use of medications to reduce fever or other infections or conditions that can cause elevated temperatures," says the nurse.

Another point to consider is that the manufacturer's instructions for use are not always followed, nor can it be ensured that the staff is trained to configure, operate and calibrate the device. “The thermometer must be calibrated according to what the manufacturer requests,” Calderón points out. “Incorrect calibration can lead to erroneous temperature readings.”

“As an element of supervision or surveillance against possible patients who have not developed respiratory symptoms, and who only have fever, it can serve as support,” says infectious disease specialist Ignacio Silva. “But not as the only measure.”

“You always have to ask if the person has respiratory or nasal symptoms and how they are taking care of themselves,” says Jorge Jorquera. It is necessary to know if the individual “has respected the quarantines, if he has maintained physical distancing, if he has good hand hygiene or if he is wearing a mask at work.” All of these questions “allow you to better guide yourself,” especially if you are considering inviting this person to your home.

Is it necessary to invest in an infrared thermometer in the house?

The thermometer is a device that everyone should have in their home. Basically it is one of the essentials in a first aid kit, but traditionally the one we have in the house is the mercury one - which you take great care of so that it does not break - or more safely a digital one, since they are now more accessible than ten years ago. But today, when taking temperatures in public places is becoming normal, is it necessary for me to also purchase an infrared one?

Expert opinion says that it is not necessary to invest in this type of device for home use in the context of this pandemic. “For mass use, when applied to large numbers of people, it works,” says Jorge Jorquera, “because one could detect a patient who is suffering from a fever and who did not know it.”

But to receive visitors in your house, it is not necessary, says the specialist and his argument is based on the criteria of each person when inviting someone. “You're not going to welcome just anyone into your house,” he says. “You hope there is awareness among guests about their symptoms.” For him, the equation is simple: “if you have symptoms, don't come.”

“The thermometer can help us detect possible cases, however, it is not reliable to prevent infections,” says Carolina Calderón. “The most important thing remains hand washing and wearing masks.”

The action of monitoring the temperature would be “one of the measures to evaluate the suspicion of covid-19,” comments Ignacio Silva. “But the truth is that it does not replace self-monitoring of symptoms.” The specialist mentions that one should never visit someone who has symptoms associated with the coronavirus. Hosts, for their part, must ensure that guests have not had contact with patients with Covid-19.

When asked whether or not to measure the temperature of visitors, the professional adds that “it depends on how concerned each person is.” This same effect would occur among those who choose to disinfect shopping packages or purchases that arrive by delivery. “It is not a mandatory recommendation, but it is a measure that contributes to prevention,” he adds.

In case you are thinking of purchasing one of these devices, Carolina Calderón suggests that “you should always read the manufacturer's recommendations, since there are different types of suppliers and a poor calibration could give us an erroneous result.” Her last recommendation is that “you also have to look at whether it is an industrial or medical type thermometer.” There has been confusion because “physically they are almost similar, that is why you have to look at the technical specifications.”