COVID-19’s pandemic has resulted in a flurry of sales of Infrared cameras; this comes with a responsibility not just for the distributor, but also the end-user. For many years temperature is the first measurement of physical property for determination of monitoring and diagnosis of health in human medicine.
For the clinician, fever is essential information in the identification of acute infections and viruses. However, the absence of evidence of fever might wrongly, reasure the clinician/technician that a virus or disease is not likely and therefore create a potentially dangerous situation if the measurement of temperature is based on poor methodology and capture.
The bad news for this methodology of fever screening is this: people screened for evidence of COVID-19 during the incubation period will not have developed symptoms so are unlikely to show up during screening.
HUMAN CORE BODY TEMPERATURE REMAINS ALMOST CONSTANT, but the temperature of peripheral body structures, (as is measured by Infrared for fever screening) fluctuates with environmental changes, behaviour, and metabolism. This will most definitely interfere with the temperatures measured during fever screening unless strict protocols are in place.
All movement and exercise depend on molecules of Adenosine Triphosphate (ATP). ATP transports chemical energy within cells for metabolism. When this compound splits into ADP & Pi (Adenosine Diphosphate and inorganic phosphate), it releases energy. This splitting of the energy of ATP molecules is used to help maintain body temperature. However, movement, exercise and behaviour change the kinetic energy of the cell, and the higher the body temperature, then the higher the metabolic temperature and visa versa. To control body temperature, we secrete sweat; this has a cooling effect and can affect the outer body structures measured during fever screening.
Others things that increase sweating is nervousness, pain, drugs, nausea, drugs and diarrhoea, as well as pregnancy and time of day. Divergent thermal environments are also responsible for fluctuating peripheral body temperatures. All of these physiologies bring issues for the reliability of fever screening, especially if the operator/technician does not take any of this information into consideration.
So where does that leave us with using IR for fever screening?
To date, many of the fever screening advice has been subpar, visual scans for promoting camera sales inaccurate and conflicting information given. No one seems to question the advice given out on how to fever screen correctly using IR. I believe it is because there is a lack of medical professionals guiding the use of this methodology. There are too many videos put together by promoters of IR equipment who are non-medical experts, they read an article or two and based on this, make a promotional video based on inaccurate information which then influences the masses.
NOTE: Surface temperature levels are affected by the environment, operational conditions, heat transfer processes of a human body and the surface characteristics.
Eye temperature for fever screening.
There is a lack of research evidence to show that the Medial Canthus or Caruncula Lacrimal (the small, pink, globular nodule at the inner corner) also known as tear duct region, is the best possible anatomy to use for fever screening in pandemic situations. Let’s remind ourselves that Medial Canthal anatomy is peripheral; it is made of skin covering sebaceous and sweat glands and is influenced by all the factors mentioned above. Areas of the eye, especially around the posterior border of the eyelid and the lacrimal caruncle, have rich capillary beds that respond to changes in blood flow resulting in localised temperature changes in humans. One of the reasons this anatomy is scanned for fever screening is, peoples faces are the most accessible anatomy for the cameras to focus on in large groups. Therefore, it is easier to set the camera to the highest temperature on the face than in more temperature accurate anatomies. In all past research using thermography, the eye temperature is lower than the ear temperature. Therefore, should this only be used as a first stage screening, in crowded places? When an individual is identified as having an above-average temperature, should they not then be pulled out of the crowd, and a second screening takes place?
The examined ear via thermometer can detect fever, defined as ≥38 oC rectally in an adult population by using an ear cut-point of 37.5 oC, but as with the eye, does not measure the exact temperature.
However, current and past research have reported that the Tympanic Membrane, (eardrum), the membrane which separates the outer and middle ears, and hypothalamus share blood supply from the carotid arteries which supply the head and neck. Current research seen in the scans above is reflective of heat from both the Tympanic Membrane and ear canal.
The eye and ear temperature in sedentary and active humans are surrogates of brain temperature.
Due to peripheral interference from metabolism, environment, behaviour, as well as other artefacts (contact lenses, glasses, eye rubbing) and poor image capture methodologies (standards and protocols) the eyes are unreliable indicators for accurate identification of fever using thermography. Over 50% of cases are reported to be missed with this methodology. When ears are scanned, there is a higher % of the success of fever detection compared to eyes. Standardisation and protocols using this methodology must also have adhered.
For reliable results, most patients will still require rectal or oral temperature measurements post fever screening using IR cameras.