Data collection
AECOPD
The electronic medical records of patients included in our retrospective cohort were divided equally to be reviewed and extracted in a systematic manner by AJP, AP, and SA. AP and JC independently reviewed the extracted data and determined the final diagnosis based on discharge diagnosis and documentation which included a synthesis of all presenting signs and symptoms, imaging, and laboratory results available over the admission. Discrepancy of the final diagnosis was then discussed between AP and JC to agree on a final diagnosis. We categorized final diagnosis into AECOPD alone or AECOPD with other conditions, or no AECOPD. Our terminology is an elaboration of that published in the 