How can we tell if someone is infected with COVID-19?

Testing for COVID-19 is important

Testing to confirm who is infected with SARS-CoV-2 has been an important strategy that has helped control the spread of COVID-19. It is important to know who is infected so we can track infected peoples movements and identify others in the community they may have come into contact with while infectious. These contacts can be tested, or asked to isolate – this is known as contact tracing.

Once someone tests positive for COVID-19 they are placed into quarantine/isolation to ensure they don’t interact with and infect other people. This can help contain, or slow the spread of the virus as removing infected people from the public means less people will be exposed to the virus.

Testing large numbers of people has been an effective strategy for many countries, and has helped governments to make decisions about pandemic restrictions. If testing shows there are low numbers of infected people in the community – restrictions can be reduced or removed altogether. If testing shows there are still high numbers of infected people in the community – restrictions can be introduced or made stricter to try protect people from becoming infected.

There are different tests which can be used to help identify people infected with COVID-19 and each of these has strengths and weaknesses. Some tests look for symptoms of the virus, some look for the virus itself and others look for evidence of our body’s response to the virus.

Looking for evidence of COVID-19 - Temperature checks to look for fever

ne common symptom people infected with COVID-19 experience is a fever. A fever is when an infection causes your body’s temperature to increase above the normal of around 37◦C. People experiencing fever might experience feeling hot, chills, body aches, sweating or weakness. If someone has a high temperature this might be an indication they are sick and experiencing fever. Checking someone’s temperature can be performed with a thermal imaging camera.

Thermal imaging cameras take pictures where hotter areas appear red and colder areas appear blue. This gives us visual information about the temperature of the object having its picture taken.

The images below show a healthy person not experiencing fever compared to someone who is sick and experiencing fever.

Canberra airport was the first in Australia to introduce screening passengers by thermal imaging to try stop the spread of COVID-19. As people who registered a high temperature were sent to a nurse to confirm if they were sick before being allowed on their flight. Other locations like hospitals, shopping centres and schools are also considering introducing thermal imaging technology to screen people before they are allowed in.

Strengths and weaknesses of thermal imaging

Strengths:

Checking people’s temperature by thermal imaging is fast, easy, cheap (once the initial camera has been purchased there are no other costs), does not require a trained medical professional and can be done with no physical contact between the person testing and the person being tested.

Weaknesses:

high body temperature recorded on the thermal camera does not mean someone is infected with COVID-19. There are a number of other reasons someone might be experiencing an increase in body temperature: recent exercise, too many layers of clothing or another illness unrelated to COVID-19. Thermal imaging will also not help diagnose COVID-19 in someone who is asymptomatic (is showing no symptoms but is infected) as they won’t experience fever. Additionally, thermal imaging relies on the surface temperature of your skin. If you have just entered a building from the cold – your skin might be a few degrees lower in temperature than normal, in this case thermal imaging would fail to identify someone with a fever.

Finally, if someone records a high temperature, further testing would be needed to confirm they are infected with COVID-19.