Pathogen
The huge death toll was caused by an extremely high infection rate of up to 50% and the extreme severity of the symptoms. One observer wrote, "One of the most striking of the complications was hemorrhage from mucous membranes, especially from the nose, stomach, and intestine. Bleeding from the ears and skin also occurred". The majority of deaths were from bacterial pneumonia, a secondary infection caused by influenza, but the virus also killed people directly, causing massive bleeding and oedema in the lungs.