Mass screening of suspected febrile patients with remote-sensing infrared thermography: Alarm temperature and optimal distance

Background/Purpose: Detection of fever has become an essential step in identifying patients who may have severe acute respiratory syndrome (SARS) or avian influenza. This study evaluated infrared thermography (IRT) and compared the influence of different imagers, ambient temperature discrepancy, and the distance between the subject and imager. Methods: IRT-digital infrared thermal imaging (IRT-DITI), thermoguard, and ear drum IRT were used for visitors to Municipal Wang Fang Hospital, Taipei, Taiwan. The McNemar and χ² test, standard Pearson correlation, ANOVA, intraclass correlation coefficient (ICC), and receiver operating characteristic curve (ROC) analysis were used to calculate the alarm temperature for each imager. Results: A total of 1032 subjects were recruited. Different distances and ambient temperature discrepancy had a significant influence on thermoguard, and lateral and frontal view DITI By ICC analysis, a significant difference was found at 10 m distance between ear drum IRT and thermoguard (r=0.45), lateral view DITI (r=0.37), and frontal view DITI (r=0.44). With ROC analysis, the optimal preset cut-off temperatures for the different imagers were: 36.05°C for thermoguard (area under the curve [AUC], 0.716), 36.25°C for lateral view DITI (AUC, 0.801), and 36.25°C for frontal view DITI (AUC, 0.812). Conclusion: The temperature readings obtained by IRT may be used as a proxy for core temperature. An effective IRT system with a strict operating protocol can be rapidly implemented at the entrance of a hospital during SARS or avian influenza epidemics.