On Sept. 21, 1918, between the start of Chicago’s epidemic and the removal of restrictions on November 16, the Windy City experienced a staggering 38,000 cases of influenza and over 13,000 cases of pneumonia.

Chicago health officials noted a spike in the number of deaths due to acute respiratory disease, signifying Chicago’s influenza epidemic had just begun. city health By September 30, there were 260 cases in the city.

The large and sudden jump in new cases led Health Commissioner Robertson to order the immediate isolation at Cook County Hospital of all known cases.