ARCHIVED - Thermal image scanners to detect fever in airline passengers, Vancouver and Toronto, 2003

Introduction

During the Severe Acute Respiratory Syndrome (SARS) outbreak of 2003, rapid population migration facilitated the spread of the disease from one country to another. In an attempt to prevent importation and exportation of the virus, the World Health Organization (WHO) made recommendations for screening of international passengers ⁽¹⁾. These recommendations included screening of passengers departing from affected areas by means of a questionnaire or interview and, in the event of an ill passenger on a flight from an affected area, isolation of that person and identification of their contacts.

In Canada, passengers arriving from affected areas were screened through a Health Alert Notice (HAN) with a questionnaire (yellow-coloured cards) and those with risk factors for SARS were assessed by a screening nurse ⁽²⁾. International passengers departing from Toronto's Pearson Airport were also screened with a HAN (cherry-coloured cards) and posters were displayed in airport terminals. Thermal image scanners, to detect passengers with elevated temperatures, a presenting symptom of SARS, were employed in Toronto Pearson and Vancouver International Airports. This report summarizes the data collected on the use of these thermal image scanners.

Results

Twelve thermal image scanners were deployed to two airports from mid-May to mid-December, 2003; however, only 11 were used. All passengers who had an elevated temperature detected by a scanner were referred to a screening nurse for a medical assessment, which included an oral temperature and administration of a standardized questionnaire for SARS.

Thermal image scanners were operational at Vancouver International Airport on 16 May 2003, and at Pearson International Airport, Toronto on 23 May 2003, for both arriving and departing passengers. A total of 4,569,759 passengers were assessed by the scanners (Table 1). An elevated temperature was detected in 1,435 people (0.031%). No person was assessed as having SARS.

Additional data were available for passengers screened at Pearson Airport between 1 September and 10 December 2003 (Table 2). Of the 733 passengers that the thermal image scanners detected as having an elevated temperature, only 49 (6.7%) had a temperature > 38.0 °C when measured with an oral thermometer. No person was assessed as having SARS.

Discussion

A total of 438 cases of SARS (251 probable cases and 187 suspect cases) were reported in Canada during the outbreak period of 23 February to 12 June 2003 ⁽³⁾. Five of these cases were travellers returning from affected areas of Asia, only three of whom were symptomatic during their flight⁽⁴⁾. The last traveller with SARS entered Canada on 1 April 2003. However, thermal image scanners were not put into operation in Canadian airports until after that date. Of persons who were exposed to SARS in Canada and then travelled and became ill elsewhere, none was symptomatic when departing this country⁽⁵⁾.

In Hong Kong, 36.3 million people underwent screening by thermal scanner; 1921 (0.00053%) were febrile; 40 of these people were admitted to hospital but none was diagnosed with SARS(6).

Thermal image scanners determine the temperature of an object by measuring the amount of infrared radiation emitted by that object; the higher the temperature, the more infrared radiation that is emitted. Their primary medical use has been in the diagnosis of breast cancer(7). Thermal scanners measure the skin and not the core temperature. Their accuracy of + or - 2° C is affected by physical activity, stress, alcohol and drug use, nicotine, caffeine, circulatory problems and injury; operator training and experience; and environmental factors, such as air temperature and currents.

Thermal scanners have not been previously used for the screening of populations for fever and there are no published clinical data on the sensitivity and specificity of scanners for this use. While they are a potential means of easily evaluating large numbers of people for fever, scanners must be studied further before their use can be recommended. Moreover, it needs to be determined whether mass screening for fever is the most effective means for detecting disease in travellers during an outbreak or whether other more "low-tech" approaches, such as increased public education, may be of more value.

Table 1. Number of passengers detected with an elevated temperature by thermal image scanner and suspected of SARS, Vancouver International and Pearson Airports, May to November 2003

Table 2. Characteristics of passengers detected with an elevated temperature by thermal image scanner, Pearson Airport, 1 September to 10 December 10, 2003

References

1. WHO. WHO recommended measures for persons undertaking international travel from areas affected by Severe Acute Respiratory Syndrome (SARS). WHO Wkly Epidemiol Rec 2003;78:97-9.

2. Health Canada. SARS screening of travellers to and from Canada, March 31, 2003. Available at: http://www.hc-sc.gc.ca/english/protection/warnings/sars/factsheet2.html. Accessed 16 January, 2004.

3. Health Canada. Canadian SARS numbers, September 3, 2003. Available at: http://www.phac-aspc.gc.ca/sars-sras/cn-cc/20030903_e.html.
   Accessed 16 January, 2004.

4. Flint J, Burton S, Macey J et al. Assessment of in-flight transmission of SARS - Results of contact tracing, Canada. CCDR 2003;29:105-10.

5. Health Canada. Summary of SARS cases potentially exposed in Canada and diagnosed internationally. April 26, 2003. Available at: http://www.phac-aspc.gc.ca/sars-sras/pef-dep/sars-es-int20030426_e.html.
   Accessed 16 January, 2004.

6. SARS Expert Committee. SARS in Hong Kong: From experience to action. October 2003. Available at: http://www.sars-expertcom.gov.hk/english/reports/reports/files/e_app4.pdf. Accessed 16 January, 2004.

7. Parisky Y, Sardi A, Hamm R et al. Efficacy of computerized infrared imaging analysis to evaluate mammographically suspicious lesions. Am J Roentgenol 2003;180:263-69.

Source: Centre for Emergency Preparedness and Response, Population and Public Health Branch, Health Canada.