Finding Fever – Flu and Border Controls

A quarantine officer monitored a thermal scanner Tuesday at Incheon International Airport in South Korea. Jung Yeon-Je/Agence France-Presse — Getty Images

Thermal scanners purchased after the SARS outbreak have been mobilized for border screening. Super-cool, but do they work to stop the spread of an epidemic?

The New York Times led with this image, but now the story link has been updated. Here’s the original text by Donald G. McNeil, Jr. on border controls:

Given extensive human-to-human transmission, the World Health Organization raised its global pandemic flu alert level on Monday, but it recommended that borders not be closed nor travel bans imposed, noting that that the virus had already spread and that infected travelers might now show any symptoms.

However, many countries are tightening border and immigration controls, and on Tuesday Britain advised against any nonessential travel to Mexico. Japan announced that it would no longer allow Mexican travelers to obtain visas upon arrival. The United States, France and Germany have also warned against nonessential travel to Mexico.

Here’s my understanding of how it works: the thermal scanner camera detects infrared radiation (IR). Basically any object emits IR which intensifies as it gets hotter. The camera has a sensor which detects IR and converts it into a temperature reading. In this system it does it visually.

However, when you first get flu, you don’t have a temperature, and the thermal scanner only measures skin temperature on your face, so an early fever (which raises your core temperature) is also not detectable.

So – does it work? Work done by Bitar et al as a followup to SARS control was published in February 2009: International travels and fever screening during epidemics: a literature review on the effectiveness and potential use of non-contact infrared thermometers In the early stages of a pandemic when less than 1% of people will be feverish, fever screening at the border is of limited use – from the paper “When we fixed fever prevalence at 1% in all studies to allow comparisons, the derived positive predictive value varied from 3.5% to 65.4% ” So thermal scanners aren’t very useful when very few people have fever.

However, check out this view from William Saletan in Slate: Heat Check – Swine Flu, Body Heat and Airport Scanner

On another note, I’m wondering why journalists don’t seem to have quick access to infectious disease specialists. In the New York Times, an environmental health epidemiologist is quoted in the debate, and here in the Cape Times, a sociologist who now specializes in the public understanding of biology. Where are the infectious disease experts? Maybe the CDC needs to draw up a list of media contacts among their top virologists and infectious disease specialists. Maybe part of science education should be a course in writing on science for the public, as well as how to write (and read!) papers.

Laurence Altman wrote a nice article in the New York Times about assessing the flu threat: Sound the Alarm? A Swine Flu Bind

For ongoing info: here’s the WHO, the CDC and if you really want to geek out: ProMED-mail.