Table 2 Criteria for tracheal lesion score

Score 0

normal histological structure

Score 1

hyperemia and inflammatory cells infiltration

Score 2

hyperemia, inflammatory cells infiltration, and edema

Score 3

hyperemia, inflammatory cells infiltration, edema, and deciliation with catarrhal exudate

Score 4

slight hyperplasia and deciliation with syncytial cell formation

Score 5

hemorrhagic patches, desquamation, and hyperplasia

Score 6

squamous metaplasia with collagen bundles and mononuclear cell infiltration