International travel may spread infectious diseases like SARS or Influenza rapidly.  On Eurosurveillance one can find an interesting article on the use of non-contact infrared thermometers (NCIT) to detect fever in passengers as a border control strategy to prevent infectious diseases from spreading. The evidence on the effectiveness of this strategy is gathered from the literature and is not very promising.

International travels and fever screening during epidemics: a literature review on the effectiveness and potential use of non-contact infrared thermometers
D Bitar, A Goubar, J C Desenclos from Department of infectious diseases, Institut de Veille Sanitaire, Saint Maurice, France

Introduction
The emergence of Severe Acute Respiratory Syndrome (SARS) in 2003 underlined the role of international travels in the rapid spread of infectious diseases and prompted countries to set up border control strategies, in order to reduce the risk of introduction of an infection.

Traditional measures such as information for travellers, self-completion of health cards or visual inspection of passengers were implemented by most countries. Several countries plan to introduce non-contact infrared thermometers (NCIT) at international airports in order to detect febrile passengers, thus to delay the introduction of a novel influenza strain.

Methods
In this review we summarise the available information on the sensitivity, specificity and predictive values of NCIT used with the objective of fever screening, in airports or other gathering areas to estimate their efficacy under the hypothesis of pandemic influenza. Three Severe Acute Respiratory Syndrome (SARS) or dengue fever interventions in airports were excluded because of insufficient information.

Results:
Six fever screening studies in other gathering areas, mainly hospitals, were included (N= 176 to 72,327 persons; fever prevalence= 1.2% to 16.9%).
Sensitivity varied from 4.0% to 89.6%, specificity from 75.4% to 99.6%, positive predictive value (PPV) from 0.9% to 76.0% and negative predictive value (NPV) from 86.1% to 99.7%. When we fixed fever prevalence at 1% in all studies to allow comparisons, the derived PPV varied from 3.5% to 65.4% and NPV was >=99%.

Discussion
The low PPV suggests limited efficacy of NCIT to detect symptomatic passengers at the early stages of a pandemic influenza, when fever prevalence among passengers would be =<1%.

External factors can also impair the screening strategy: passengers can hide their symptoms or cross borders before symptoms occur. These limits should be considered when setting up border control measures to delay the pandemic progression.

The psychological reassuring effect on the public can influence the decision to implement such screening, as was the case in Singapore and Canada, but these countries also recognised that the public may loose confidence in this measure if an undetected case had entered the country and generated secondary cases.

Because public perceptions are important, policy makers may feel some pressure to use NCIT 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.