Exposure and outcome measures:
The primary exposure was clinical respiratory illness (CRI) defined as self-reported history of ≥2 respiratory symptoms (fever, cough, sore throat, runny nose and difficulty breathing) within prior 7 days of date of onset of AMI (32, 33). The secondary exposure was baseline qRT-PCR confirmed influenza A or B. In the current study the main predictor variables of interest were CRI and laboratory evidence of Influenza, and the outcome variables were AMI and AMI sub-types.