Cryo s

i) Saliva sample collection: A Saliva collection tube (ISO9001 certified; Cryo.s™; Greiner Bio-One GmbH, Frickenhausen, Germany) was used. The samples were collected by physicians once prior to shifts commencing and once after at least 18 h. Before sampling, the mouth was rinsed three times with distilled water (30 ml NS for 1 min) and subjects sat quietly for 5 min in front of a mirror in an upright sitting position; the head slightly leaned forward and the eyes were kept open for masticatory movement to stimulate the secretion of saliva. When a certain amount of saliva was accumulated in the lower jaw, the tongue reached the upper jaw, the mouth was opened and the tongue was naturally lifted to form a V shape in the lower lips, allowing the saliva to flow into the saliva collection tube prepared in advance. Then 2 ml of saliva was collected and the interval between sampling and eating and the recipe characteristics were recorded. ii) Saliva sample storage: The sample was labeled by the science assistant, and stored at −70°C. iii) Saliva sample detection was conducted by the National Key Laboratory of Institute of Infectious Diseases Prevention and Control of Chinese Center for Disease Control and Prevention (MALDI-TOF MS).