Diffuse alveolar damage (DAD) was reported in 88% of patients with COVID-19. This is similar to both H1N1 (90%) and SARS (98%).

Pulmonary microthrombi was reported in 57% of patients with COVID-19. This was similar to SARS (58%) and also observed in H1N1 (24%).

Organising fibrosis was observed in 52% of COVID-19 patients and was reported in 40% of H1N1 and 47% of SARS cases.

57% of COVID patients reported microthrombotic disease, and this was more similar to SARS with 58% and less similar to HIN1 with 24% of cases.

Acute neutrophilic pneumonia was reported in 32% of COVID-19 patients, 30% of H1N1 patients and 31% of SARS patients.

AFOP was observed in 4% COVID-19 patients and was a rare finding in H1N1 and SARS.

These findings suggest that diffuse alveolar damage is a predominant histopathologic pattern that is identified in lung pathology from COVID-19, H1N1 and SARS patients. However, research in this area must continue as future studies are critical to characterise the scope of lung pathology across the spectrum of COVID-19 severity and to determine which interventions could help prevent respiratory failure in COVID-19 patients.

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