Normal body temperature is between 36.1–37.8 °C, above this temperature you are normally classed as having a fever which is one of the symptoms of flu.
Normally to take someones temperature requires the use of an oral thermometre however this can not be used for hundreds of people leaving an aircraft due to the time it would take, another way is to take a picture of person with a thermal image camera, it looks like a normal camera but instead of a taking picture of light it takes a picture of heat, the camera translates temperatures into colours, this way people can be checked quickly if they have an elevated temperature. The procedure is none evasive, I understand that those concerned with hot flushes should not be as the camera can tell the difference as it is looking at overall body temperature.
Look at the following link it shows a group of people as a thermal image, none of them are showing a fever.
http://img.timeinc.net/time/photoessays ... ers_01.jpg
Dave
Dave