Wednesday, January 2, 2013

Border Screening for Detecting Influenza in Arriving Airline Travelers

Thermal scanning of passengers- source:
Winter is upon us in the Northern Hemisphere and so is influenza. Not long ago we were in the midst of the H1N1 Pandemic.  During that time, I traveled to Honduras and was subjected, like all passengers, to a temperature screen at the airport. The purpose? To detect influenza. Anyone with a knowledge of infectious diseases will tell you that fever is neither sensitive nor specific to influenza. 

Today a came across this paper on the effectiveness of border screening for detecting influenza in airline travelers, published in the American Journal of Public Health.

Using a cross sectional study design, the investigators collected data from travelers in  a New Zealand international airport. Forms were returned by 15, 976 (68%) travelers. Of these, 17% reported at least 1 influenza symptom, with runny or blocked nose (10%) and cough (8%) most common. Respiratory specimens were obtained from 3769 travelers. Estimated prevalence of influenza was 1.1% (4% among symptomatic, 0.2% among asymptomatic). The sensitivity of screening criteria ranged from 84% for “any symptom” to 3% for a fever of 37.8 °C or greater. The positive predictive value was low for all criteria.

These data suggest that screening air travelers for symptoms of influenza is of limited value. If one were to screen for fever only, the effort is largely useless. If the screening is expanded to include 'any symptom', then more (but not all) cases of influenza would be detected. This latter strategy would also identify people with influenza-like symptoms who are not infected with influenza. 

As a public health intervention, the detection of influenza in airline travelers is of limited value.
An earlier study on thermal screening of passengers, published in PLOS ONE can be found here. The conclusion is similar.

Bon voyage.

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