Table 2. Histopathological scoring system (also see Supporting information).

Structure	Lesion	Extent	Score
1. Bronchial lumens (S1A–S1D Fig)	Neutrophils	None	0
		<10 per airway	1
		11–50 per airway	2
		>50 per airway	3
2. Bronchiolar lumens (S2A–S2D Fig)	Neutrophils	None	0
		<10 per airway	1
		11–50 per airway	2
		>50 per airway	3
3. Bronchial/bronchiolar	Epithelial necrosis /degeneration	None	0
		Mild	1
		Moderate	2
		Severe	3
4. Perivascular	Inflammation / fibrin	None	0
		Mild	1
		Moderate	2
		Severe	3
5. Alveoli / interstitium (S3A–S3D Fig)	Edema	None	0
		<25%	1
		25–50%	2
		>50%	3
6. Alveoli (S4A–S4D Fig)	Inflammatory cells	None—few	0
		Mild increase	1
		Moderate	2
		Marked	3
7. Interstitial (S5A–S5D Fig)	Inflammatory cells	None—few	0
		Mild increase	1
		Moderate	2
		Marked	3
8. Anywhere (S6A–S6D Fig)	Hemorrhage / necrosis / fibrin	None	0
		Up to 5% of section	1
		5–50% of section	2
		>50% of section	3

The above scoring system also allowed for qualitative description of additional features, such as thrombosis, emphysema, fibrosis and vasculitis. Original max score per sample 8 x 3 = 24, modified max score 6 x 3 = 18. The grey sections highlight the criteria removed from the original scoring system to improve inter-scorer correlation.