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Volume 26, Number 9—September 2020

Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings—International Travel-Related Measures

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To the Editor: Ryu et al. reviewed international travel–related measures for pandemic influenza, including screening travelers for infection (1). Although the authors did not review the performance of individual screening tools, Ryu et al. reported that no evidence exists to indicate that screening has any substantial effect on preventing the spread of pandemic influenza.

However, government officials continue to call for international airport screening guidelines as a crucial measure to control coronavirus disease. Therefore, differentiating between screening tools with poor technical performance and those approved for fever detection is worthwhile. For example, the Food and Drug Administration (FDA) states that thermal scanners should not be used as standalone tools for fever detection (2). FDA instead recommends that officials use handheld infrared thermometers as screening tools.

Thermal scanners use long-wave infrared to generate heat map images of persons and objects. This technology records surface temperature; however, fever determination requires a measurement of core body temperature. A study with 1,109 participants showed a correlation with core temperature of merely R2 = 0.41 for the most commonly used thermography region, the forehead (3). Performance of R2 = 0.69 was achieved only with overlaid standard camera video and complex free-form deformation models. Participants were assessed individually, after being seated for 15 minutes, without topical cosmetics or eyewear, at a stable ambient temperature and humidity, and without nearby infrared radiation sources. These conditions are rarely, if ever, met in the airport setting.

Despite this evidence, costly thermal scanners have been deployed at airports in many countries. In contrast, inexpensive infrared thermometers are FDA approved for core temperature approximation. At their current performance, thermal scanners must be clearly distinguished from infrared thermometers, and thermal scanning should not be recommended for fever screening.


Jaspreet PannuComments to Author 
Author affiliation: Leland Stanford Junior University, Stanford, California, USA



  1. Ryu  S, Gao  H, Wong  JY, Shiu  EYC, Xiao  J, Fong  MW, et al. Nonpharmaceutical measures for pandemic influenza in nonhealthcare settings. Emerg Infect Dis. 2020;26:9616. DOIPubMedGoogle Scholar
  2. US Food and Drug Administration. Enforcement policy for telethermographic systems during the coronavirus disease 2019 (COVID-19) public health emergency. 2020 Apr 16 [cited 2020 May 1]
  3. Zhou Y, Ghassemi P, Pfefer J, Casamento J, McBride D, Chen M, et al. Large-scale clinical study of ‘point of care’ thermal imaging for febrile patient detection: towards optimal non-contact diagnostics in disease pandemics. In: Gannot I, editor. Proceedings volume 10872: optical fibers and sensors for medical diagnostics and treatment applications XIX. SPIE BiOS 10872; 2019 Mar 4; San Francisco, CA, USA. Bellingham (WA): Society of Photo-Optical Instrumentation Engineers; 2019 [cited 2020 May 1]


Cite This Article

DOI: 10.3201/eid2609.201990

Original Publication Date: June 03, 2020

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Jaspreet Pannu, Leland Stanford Junior University, 300 Pasteur Dr, Stanford, CA 94305, USA

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Page created: May 21, 2020
Page updated: August 20, 2020
Page reviewed: August 20, 2020
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.