Ultrasonic humidifier lung as a mimic of COVID-19

Chest computed tomography (CT) has been used to complement coronavirus disease 2019 (COVID-19) diagnosis due to its high sensitivity. However, owing to the low specificity of CT findings, differential diagnosis is essential. The typical CT findings of COVID-19 include ground-glass opacifications and consolidations with predominant distribution in bilateral, peripheral, and subpleural parts of the lung. These imaging findings are non-specific and may resemble other lung conditions, including ultrasonic humidifier lung, which is a condition that develops on inhaling aerosols generated by ultrasonic humidifiers. We present two patients with initial symptoms similar to COVID-19. CT examination revealed centrilobular nodules and consolidations with upper lobe-predominant distribution, although atypical for COVID-19, but key findings for ultrasonic humidifier lung. Therefore, ultrasonic humidifier lung could be a differential diagnosis for COVID-19 in dry environments. Characteristic CT findings and a history of ultrasonic humidifier use are critical to the final diagnosis.