Table 2. Histologic lung lesion scoring criteria.

Score	Bronchitis	Bronchiolitis	Syncytial cells	Epithelial necrosis (bronchi or bronchioles)	Epithelial hyperplasia (bronchi, bronchioles)	Neutrophil (in bronchi, bronchioles or alveoli)	Bi nodules (these are peribronchiolar lymphocytic infiltrates)	Vessel nodules (lymphocytic infiltrates around blood vessels)	Eosinophilic infiltrates in bronchi or bronchioles, alveoli	Eosinophilic infiltrates in vessels	Eosinophils in vessel lumens
0	no remarkable lesions	no remarkable lesions	none	none	none	none	none	none	none	none	none
1	minimal detectable lymphoplasmacytic infiltrates in lamina propria and adventitia	minimal detectable lesion (epithelial degeneration) in one or a few bronchioles per 20x field	one distinct syncytial cell	minimally detectable in one or a few per 20x field	minimally detectable in one or a few airways per 20x field	minimally detectable	earliest detectable lymphocytic infiltrates in the adventitia	earliest detectable lymphocytic infiltrates in the adventitia	minimally detectable	minimally detectable	minimally detectable
2	segmental to circumferential infiltrates	epithelial degeneration involving less than 10% of the airway lumen; minimal neutrophils, cell debris; adventitial lymphocytes in multiple bronchioles	up to three in three 20x fields	10% in multiple airways per 20x field	10% of airway per 20x field	10 or less neutrophils in one or a few airways/alveoli	segmental to circumferential infiltrates	segmental to circumferential infiltrates	up to five eosinophils in one to several airways/alveoli per 20x field	up to five eosinophils associated with a vessel	up to five in one or a few vessels
3	dense infiltrates	epithelial degeneration involving >10–50% of the airway lumen with cell debris, neutrophils; adventitial lymphocytes; multiple bronchioles	more than three in three 20x fields	10–50% in multiple airways per 20x field	10–50% in multiple airways per 20x field	10 or more neutrophils in several airways/alveoli	circumferential infiltrates that expand more than three cells wide	circumferential infiltrates that expand more than three cells wide	over five in over five airways per 20x field	> five in over five vessels per 20x field	> five in over five vessels
4	infiltrates with nodular aggregates	circumferential bronchiolitis with dense adventitial lymphocytes; multiple bronchioles	Numerous in three 20x fields	circumferential in multiple airways	circumferential	10 or more involving many/most airways/alveoli	circumferential infiltrates that form nodules	circumferential infiltrates with nodules	dense accumulations of eosinophils	dense accumulations of eosinophils	dense accumulations