Diagnostic accuracy of infrared thermal imaging for detecting COVID-19 infection in minimally symptomatic patients

Abstract

Introduction: Despite being widely used as a screening tool, a rigorous scientific evaluation of infrared thermography for the diagnosis of minimally symptomatic patients suspected of having COVID-19 infection has not been performed.

Methods: A consecutive sample of 60 adult individuals with a history of close contact with COVID-19 infected individuals and mild respiratory symptoms for less than 7 days and 20 confirmed COVID-19 negative healthy volunteers were enrolled in the study. Infrared thermograms of the face were obtained with a mobile camera, and RT-PCR was used as the reference standard test to diagnose COVID-19 infection. Temperature values and distribution of the face of healthy volunteers and patients with and without COVID-19 infection were then compared.

Results: Thirty-four patients had an RT-PCR confirmed diagnosis of COVID-19 and 26 had negative test results. The temperature asymmetry between the lacrimal caruncles and the forehead was significantly higher in COVID-19 positive individuals. Through a random forest analysis, a cut-off value of 0.55°C was found to discriminate with an 82% accuracy between patients with and without COVID-19 confirmed infection.

Conclusions: Among adults with a history of COVID-19 exposure and mild respiratory symptoms, a temperature asymmetry of ≥ 0.55°C between the lacrimal caruncle and the forehead is highly suggestive of COVID-19 infection. This finding questions the widespread use of the measurement of absolute temperature values of the forehead as a COVID-19 screening tool.

Keywords: COVID-19; diagnosis; machine learning; screening; thermography.

FIGURE 1

Infrared thermograms. Digital infrared thermograms of a healthy control (A), a confirmed COVID‐19 negative patient (B) and a confirmed positive COVID‐19 patient (C) are shown. The images were converted into greyscale values, and the regions of maximum temperature values selected in red. Non‐COVID‐19 subjects show similar maximum temperature distribution in the lacrimal caruncles and forehead (crosses). COVID‐19 positive individuals show significantly higher temperature values on the lacrimal caruncles than on the forehead, thereby the forehead is not selected as a “hotspot” when thresholding the image

FIGURE 2

Infrared thermogram analysis. The average temperature of the forehead and lacrimal caruncles was measured and analysed. No significant differences in forehead absolute temperature were found across groups. However, the average lacrimal caruncle temperature in controls was found to be lower than those in COVID‐19 negative and positive patients, although the differences were significant only between controls and the latter group (A). When the temperature distribution was analysed as the temperature asymmetry between the forehead and caruncle, significant differences between groups were found (B). COVID‐19 individuals showed the largest temperature asymmetry, followed by COVID‐19 negative individuals and controls. ** P < .01, *** P < .001