S.A.R.S. & Avian Flu Screening

SARS (Sudden Acute Respiratory Syndrome) has become an avenue for misguided and/or profiteering individuals to attempt to become the saviour of the world by being the person who develops an AI/SARS screening protocol.

NON-CONTACT THERMAL IMAGING IS SIMPLY NOT SUITED TO AI/SARS SCREENING.

We have received dozens of enquiries from people thinking of screening the masses at airports, transit terminals etc. to find those with fevers instantly.

The sad fact is that the technology is not suited to this purpose.  Those who say otherwise either misunderstand how thermal imaging works OR are deliberately trying to cash in on the heightened potential for profit because of the fear factor.

To accurately scan for fever in a mass screening situation, current ear thermometer technology used in most hospitals is the most appropriate, with each and every person (not just passengers) being checked individually upon entering the departure territory.

To effectively slow SARS on aircraft, the logical place to do this is during the scanning of passenger's luggage when entering the departure areas.  Once a SARS case in in an aircraft, it is much more likely to spread in the enclosed and recirculated environment of the passenger cabin.

WHY THERMAL IMAGING IS NOT SUITED FOR SARS SCREENING
(including Avian Influenza)
Last updated 23-May-2008

It is proposed that Thermal Imaging be used to scan large numbers of people to find those who are in a clinically febrile state (have a fever) as an indicator of potential AI/SARS carriers.

Four simple factors make AI/SARS screening through thermography improbable at best:

The error rate of Thermal Imaging equipment is typically ±2% or at least 1 degree Celsius ('whichever is the larger' according to many manufacturers of thermographic equipment). 

Whilst most detectors are capable of differentiating temperatures within a tenth of a degree, this is a relative measurement to the surrounding areas. 

This is perfectly acceptable in clinical Thermal Imaging as it is not the absolute temperature which is significant, but the comparative measurements with the surrounding tissues.  Most imaging systems on the market have trouble delivering an error rate less than two percent. 

Body temperature is generally considered normal between 36.2^oC to 37.2^oC.  Two percent of 37^oC = 0.74 degrees.  CDC considers a 38^oC temperature as the threshold of suspicion for a potential SARS case.

The expected plus or minus error rate at normal body temperatures equates to a 1.4^oC variance. Now most manufacturers term the error rate as ±2% or 1^oC, "whichever is the greater".  Many manufacturers actually state a minimum two degree variance.

A large number of people with fevers could slip through on the minus side and an equally large number of people could be indicated as having a fever.  Non-contact Thermal Imaging simply does not have the finite qualitative and quantitative resolution to act as a SARS screening device.

An absolute temperature measurement is required for body temperature taking.  Thermal Imaging technology requires a reference temperature (black body) so it can calculate infrared emissions as a temperature accurately. 

The thermal stability of the receiver unit and the atmospheric or ambient temperature also play large roles in this process.  These are some of the factors which can increase the error rate described in the point above. 

Airports or transit lounges can not establish environmental controls for effective Thermal Imaging at the level which is required for potential SARS screening, assuming that all other factors could be negated. 

To reliably produce accurate non-contact thermograms;

1. The environmental temperature must be controlled to within a two degree (Celsius) temperature band to allow consistency in imaging.
2. Environmental infra-red pollution must be ELIMINATED.  If this is not achieved the Thermal Imager will yield a completely inaccurate and unusable result.  Sunlight, incandescent light, food services and any other heat source (like hot windows, nearby jet engines etc.) produce copious quantities of infrared energy which will reflect from the person to the scanner, rending the image useless.
3. Other environmental aspects like humidity and air-flow must be consistently controlled as these are also critical factors effecting dramatically the resulting thermal image.  Transit terminals can not be controlled in any fashion close to this requirement.

Measuring the body's core temperature can not be done effectively AND reliably at the skin's surface. 

Body temperature measurement can only be conveniently performed deep in the ear canal where cooling breezes, heating spectacle contact points and many other factors are not active.  Such accuracy is far more achievable with existing temperature measuring devices requiring far less operator [technical] skill. 

The inside corner of the eye is about the only other place commonly exposed which can reflect the core body temperature in general terms.  Unfortunately the eye region is unsuited to Thermographic screening for marginal febrile conditions (fevers) as it is still subject to cooling breezes in flight, localised irritation (rubbing the eyes when sleepy for example) and shielding from eye wear.

For this to make sense, just remember the last time you had a breeze on your arm or foot and how long it took to warm back up.  A person who is hot on a plane will direct a vent at themself to cool down.  The air stream will hit the face first, cooling the very areas many are suggesting for the screening process.  Tears or perspiration will act as a dramatic surface coolant, be they from emotion, irritation or whatever.  These factors will lead to many false negatives (saying the person is clear when they are sick).

Having spectacles on, rubbing the eyes when tired, dry or irritated will all dramatically increase surface temperature, leading to many false positives (saying the person is a potential problem when they are not sick).

IN SUMMARY - It would be wonderful if we could set up a simple mass screening procedure for SARS.  Logic and common sense shows that Thermal Imaging can-not-be and is-not that "magic bullet" because:

1. Thermal Imaging (non-contact) scanners and devices simply do not offer the required quantitative accuracy (lack of error).
2. Airports CAN NOT offer an environment controlled enough for accurate scanning.
3. The body does not offer a surface suited to accurate and reliable temperature measurement other than possibly the interior of the deep ear canal.