Devices meant to detect high body temperatures as a clue for infectious diseases may prove more reassuring than effective
How does a financial services conference expecting thousands of attendees coming into the US from more than 130 countries try to keep participants safe from Ebola? It takes their temperature.
Sibos, a gathering of financial experts being held in Boston this week, emailed attendees on Monday, before the disclosure of the first case of Ebola to be diagnosed in the US, to inform them that it would, in addition to its typical metal detectors, be employing “thermal scanners” at each entrance to the conference “to detect elevated body temperatures and possible infectious diseases”.
The idea behind using these scanners, most models of which look like a smaller version of the radar guns police use to catch speeding motorists, is that they can detect people who have a fever, one of the symptoms of Ebola, as well as many other infectious agents.
This kind of screening has long been used as part of the response to outbreaks like Ebola, Sars and influenza. People flying out of the West African countries where the Ebola epidemic is currently centered have their temperatures taken before boarding, and if it is elevated, they are tested for the virus.
Whether doing this – and especially by way of these scanners – is effective is another matter. Some researchers have called the scanners reassuring, and not much more.
Checking body temperature isn’t a sure-fire way to find individuals infected with Ebola. People can carry the virus for up to three weeks before showing symptoms, and are not contagious during that period. The patient in the US case, Thomas Eric Duncan, was reportedly asymptomatic when he travelled from Liberia to Dallas.
In a guidance paper produced by the Centers for Disease Control and Prevention for airport and public health officials, the agency lists what it sees as problems with the devices, including cost, lack of precision, need for frequent calibration and maintenance and training requirements. Testing efficacy to judge the scanners write large is difficult because of the many and changing models available.
While such scanners can be good at ruling out people without fevers, the CDC said, they have a wide and varying range of efficacy at finding people with fevers depending on environmental conditions and even the age of the person being scanned. The FDA approved the devices for use only with more conventional methods of taking someone’s temperature, such as a mercury thermometer or color-changing strips.
“Policy makers may feel some pressure to use [non-contact infrared thermometers],” said French researchers at the Institut de Veille Sanitaire. “But the decision making process should not ignore the poor scientific evidence on NCIT’s efficacy to delay the introduction of a novel influenza strain.”
“The psychological reassuring effect on the public can influence the decision to implement such screening, as was the case in Singapore and Canada,” said the same study from Institut de Veille Sanitaire. “But these countries also recognised that the public may lose confidence in this measure if an undetected case had entered the country and generated secondary cases.”