Noncontact Body Temperature Measurement: Uncertainty Evaluation and Screening Decision Rule to Prevent the Spread of COVID-19

Abstract

The need to measure body temperature contactless and quickly during the COVID-19 pandemic emergency has led to the widespread use of infrared thermometers, thermal imaging cameras and thermal scanners as an alternative to the traditional contact clinical thermometers. However, limits and issues of noncontact temperature measurement devices are not well known and technical–scientific literature itself sometimes provides conflicting reference values on the body and skin temperature of healthy subjects. To limit the risk of contagion, national authorities have set the obligation to measure body temperature of workers at the entrance to the workplace. In this paper, the authors analyze noncontact body temperature measurement issues from both clinical and metrological points of view with the aim to (i) improve body temperature measurements accuracy; (ii) estimate the uncertainty of body temperature measurement on the field; (iii) propose a screening decision rule for the prevention of the spread of COVID-19. The approach adopted in this paper takes into account both the traditional instrumental uncertainty sources and clinical–medical ones related to the subjectivity of the measurand. A proper screening protocol for body temperature measurement considering the role of uncertainty is essential to correctly choose the threshold temperature value and measurement method to access critical places during COVID-19 pandemic emergency.

Reliability of Body Temperature Measurements Obtained with Contactless Infrared Point Thermometers Commonly Used during the COVID-19 Pandemic

“…The knowledge of these cautions give both operators and the individuals being screened a better understanding of the de facto limits of non-contact infrared devices. In addition, our data support the conclusions of Dell’Isola et al [ 22 ] that, to improve the reliability of screenings to prevent the spread of COVID-19 disease, proposed the following: To punctually establish the measurement conditions and method; To set a fixed temperature threshold reference, by considering an assigned measurement body site; To accurately estimate the measurement uncertainty, taking into account the main contributions at the real operative measurement conditions; To transpose the threshold reference value as a function of the body site used; …”

“…Based on analyses performed in the laboratory using these artificial heat sources, the authors concluded that two out of the three devices suffered from large measurement errors falling far outside the accuracy range stated by their manufacturers, as well as the medical standard to which these devices are intended to adhere. Finally, in a very recent paper, Dell’Isola et al [ 22 ] carefully analysed the effects of many metrological and subjective issues on the reliability of the body temperature measurement. They clarified that the body temperature measurement is influenced by the unavoidable instrumental uncertainties and by the operator’s ability, but also by numerous other quantities such as: (a) the emissivity and the reflection coefficient of the emitting skin surface; (b) the transmission coefficient of the medium between the sensor and the target; (c) the average radiant temperature of the measurement environment (i.e., the reflected temperature); (d) the distance and consequent size of the target (effect of the size of the source).…”

SARS-CoV-2 (Covid-19) workplace temperature screening: Seasonal concerns for thermal detection in northern regions

“…To address the temperature underestimation of IR laser thermometers on forehead skin measurements, evidence suggests that an indoor acclimatization period is still required when exposed to ambient temperatures to improve the accuracy of the measurement (H.-Y. Chen et al, 2020 ; Dell'Isola et al, 2021 ). Knowing that the IR laser thermometers also underestimate skin temperatures when exposed to varying outdoor conditions ( Figure 6 ), it can be hypothesized that in order to provide a more reliable estimation of the temperature and increase effectiveness in fighting the COVID-19 pandemic spread, a correction factor or uncertainty budget ( Dell'Isola et al, 2021 ) needs to be applied to the registered temperature.…”

An Overview of Thermal Infrared Imaging-Based Screenings during Pandemic Emergencies

“…In order to provide an accurate and reliable procedure for large-scale fever detection, Dell'Isola et al [58] proposed to perform a double-step measurement protocol. In the first step, contactless body temperature measurements were provided, setting a temperature threshold of 37.5 • C, considering all the measurement uncertainty due to the real operative measurement conditions.…”