Health

Can thermal cameras help spot coronavirus?

Thermal imaging camera in use at a train station in Bilbao, May 2020 Image copyright Reuters
Image caption A thermal imaging camera in use at a train station in Bilbao, May 2020

As lockdowns ease, thermal imaging cameras are popping up in all sorts of public places to assess the state of people's health.

What do thermal imaging cameras do?

Using infrared technology, thermal cameras detect radiating heat from a body - usually from the forehead - and then estimate core body temperature. These cameras are an extremely powerful tool, often deployed by fire fighters to track smouldering embers and police to search for out-of-sight suspects.

But they are not designed to be medical devices. So how useful are they in the current pandemic?

They can give a reasonable measure of skin temperature, to within half a degree - but that's not the same as body temperature.

"These devices, in general, are less accurate than medical device thermometers like those you stick in the ear," says Derek Hill, professor of medical imaging science from University College London.

What is normal body temperature?

About 37C (98.6F). A high temperature is usually considered to be 38C or over. But normal temperature can vary from person to person and change during the day. It can also fluctuate during a woman's monthly cycle.

Taking an accurate reading of core body temperature isn't easy. Although it can be measured on the forehead, in the mouth, the ear and the armpit, the most accurate way is to take a rectal reading.

Stock image of a woman running a temperature
Getty Images
Body temperature

  • 37°C(98.6°F) normal body temperature

  • 38°C(100.4°F) or above, high temperature/fever

    Source: NHS

    Do thermal cameras detect coronavirus?

    No, they only measure temperature. A high temperature or fever is just one common symptom of the virus. Others include nausea, headaches, fatigue and loss of taste or smell. But not everyone with the virus gets a high temperature and not everyone with a high temperature is infected with coronavirus.

    So thermal cameras alone will miss infected people with other symptoms or no symptoms at all - known as false negatives. They will also identify people unwell with a fever for another reason - known as false positives.

    So are thermal cameras useful?

    On its own, temperature screening "may not be very effective" says the World Health Organization. Cameras have to be set up correctly and take account of ambient temperature. A risk is that cameras can lull operators into a false sense of security.

    "They are… only one tool among many," says James Ferryman, professor of computational vision, from the University of Reading.

    What if I'm wearing a face mask or covering?

    "Heat radiating from the skin will likely be impacted by wearing face masks," says Prof Ferryman.

    That's why most temperature measurements are based on the forehead, which is usually exposed.

    Will I be hotter if I've been exercising?

    Not necessarily. Skin temperature actually goes down during exercise as sweat appears on the surface of the skin.

    The body is pretty good at regulating its temperature even after exercise, so it would have to be really quite high to show up.

    How else can my temperature be taken?

    With portable thermometers pointed at foreheads. They don't need to touch the skin, but do need to be within a few centimetres of it. While accurate to a fraction of a degree on skin temperature, they correctly detect fever about 90% of the time compared with a rectal thermometer, Prof Hill says.

    Where can I expect to be temperature tested?

    Thermal scanners are now in place at some UK airports - including Bournemouth. Temperature screening is being trialled for some passengers at Heathrow, while Manchester Airport says equipment is also being tested - but results will not be communicated to passengers or "used to influence whether a customer can travel". Portsmouth international ferry port has also installed a thermal scanner to screen departing passengers.

    Schools are deploying hand-held laser thermometers to check children each morning. And some employers are looking at introducing staff-testing in workplaces.

    Image copyright Getty Images
    Image caption Digital thermometers are being used in schools to check children

    At work, do I have to submit to a temperature test?

    Under UK employment law, individuals must agree before an employer can temperature-screen members of staff. Some work contracts will already allow for this type of test to be carried out, by so-called "implied consent".

    If employees do not consent - and there is no pre-agreed policy covering the situation - then taking someone's temperature is unlawful, says the professional body for HR and people development. Employers must also handle the medical information they gather fairly and transparently - according to the Information Commissioner.

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    CoronaVirus translator

    What do all these terms mean?

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    • Antibodies test

      A medical test that can show if a person has had the coronavirus and now has some immunity. The test detects antibodies in the blood, which are produced by the body to fight off the disease.

    • Asymptomatic

      Someone who has a disease but does not have any of the symptoms it causes. Some studies suggest some people with coronavirus carry the disease but don't show the common symptoms, such as a persistent cough or high temperature.

    • Containment phase

      The first part of the UK's strategy to deal with the coronavirus, which involved trying to identify infected people early and trace anyone who had been in close contact with them.

    • Coronavirus

      One of a group of viruses that can cause severe or mild illness in humans and animals. The coronavirus currently sweeping the world causes the disease Covid-19. The common cold and influenza (flu) are other types of coronaviruses.

    • Covid-19

      The disease caused by the coronavirus first detected in Wuhan, China, in late 2019. It primarily affects the lungs.

    • Delay phase

      The second part of the UK's strategy to deal with the coronavirus, in which measures such as social distancing are used to delay its spread.

    • Fixed penalty notice

      A fine designed to deal with an offence on the spot, instead of in court. These are often for driving offences, but now also cover anti-social behaviour and breaches of the coronavirus lockdown.

    • Flatten the curve

      Health experts use a line on a chart to show numbers of new coronavirus cases. If a lot of people get the virus in a short period of time, the line might rise sharply and look a bit like a mountain. However, taking measures to reduce infections can spread cases out over a longer period and means the "curve" is flatter. This makes it easier for health systems to cope.

    • Flu

      Short for influenza, a virus that routinely causes disease in humans and animals, in seasonal epidemics.

    • Furlough

      Supports firms hit by coronavirus by temporarily helping pay the wages of some staff. It allows employees to remain on the payroll, even though they aren't working.

    • Herd immunity

      How the spread of a disease slows after a sufficiently large proportion of a population has been exposed to it.

    • Immune

      A person whose body can withstand or fend off a disease is said to be immune to it. Once a person has recovered from the disease caused by the coronavirus, Covid-19, for example, it is thought they cannot catch it again for a certain period of time.

    • Incubation period

      The period of time between catching a disease and starting to display symptoms.

    • Intensive care

      Hospital wards which treat patients who are very ill. They are run by specially-trained healthcare staff and contain specialist equipment.

    • Lockdown

      Restrictions on movement or daily life, where public buildings are closed and people told to stay at home. Lockdowns have been imposed in several countries as part of drastic efforts to control the spread of the coronavirus.

    • Mitigation phase

      The third part of the UK's strategy to deal with the coronavirus, which will involve attempts to lessen the impact of a high number of cases on public services. This could mean the NHS halting all non-critical care and police responding to major crimes and emergencies only.

    • NHS 111

      The NHS's 24-hour phone and online service, which offers medical advice to anyone who needs it. People in England and Wales are advised to ring the service if they are worried about their symptoms. In Scotland, they should check NHS inform, then ring their GP in office hours or 111 out of hours. In Northern Ireland, they should call their GP.

    • Outbreak

      Multiple cases of a disease occurring rapidly, in a cluster or different locations.

    • Pandemic

      An epidemic of serious disease spreading rapidly in many countries simultaneously.

    • Phase 2

      This is when the UK will start to lift some of its lockdown rules while still trying to reduce the spread of coronavirus.

    • PPE

      PPE, or personal protective equipment, is clothing and kit such as masks, aprons, gloves and goggles used by medical staff, care workers and others to protect themselves against infection from coronavirus patients and other people who might be carrying the disease.

    • Quarantine

      The isolation of people exposed to a contagious disease to prevent its spread.

    • R0

      R0, pronounced "R-naught", is the average number of people who will catch the disease from a single infected person. If the R0 of coronavirus in a particular population is 2, then on average each case will create two more new cases. The value therefore gives an indication of how much the infection could spread.

    • Recession

      This happens when there is a significant drop in income, jobs and sales in a country for two consecutive three-month periods.

    • Sars

      Severe acute respiratory syndrome, a type of coronavirus that emerged in Asia in 2003.

    • Self-isolation

      Staying inside and avoiding all contact with other people, with the aim of preventing the spread of a disease.

    • Social distancing

      Keeping away from other people, with the aim of slowing down transmission of a disease. The government advises not seeing friends or relatives other than those you live with, working from home where possible and avoiding public transport.

    • State of emergency

      Measures taken by a government to restrict daily life while it deals with a crisis. This can involve closing schools and workplaces, restricting the movement of people and even deploying the armed forces to support the regular emergency services.

    • Statutory instrument

      These can be used by government ministers to implement new laws or regulations, or change existing laws. They are an easier alternative to passing a full Act of Parliament.

    • Symptoms

      Any sign of disease, triggered by the body's immune system as it attempts to fight off the infection. The main symptoms of the coronavirus are a fever, dry cough and shortness of breath.

    • Vaccine

      A treatment that causes the body to produce antibodies, which fight off a disease, and gives immunity against further infection.

    • Ventilator

      A machine that takes over breathing for the body when disease has caused the lungs to fail.

    • Virus

      A tiny agent that copies itself inside the living cells of any organism. Viruses can cause these cells to die and interrupt the body's normal chemical processes, causing disease.

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