Prevalence of CRI among all AMI cases, and sub-groups of AMI cases:
Descriptive analysis was performed to determine the prevalence (frequencies and percentages) of CRI and qRT-PCR confirmed influenza among all AMI cases as well as among various sub-groups of AMI cases. The prevalence of CRI and influenza among the enrolled patients was estimated by study seasons: during 2017 annual influenza season (1st May to 31st October, 2017), 2017/2018 non-influenza season (November 1, 2017 to April 30, 2018) and 2018 annual influenza season (1st May to 31st October, 2018). The sub-groups of AMI cases included the binary variables created for non-ST-Elevation Myocardial Infarction (NSTEMI) or, ST-Elevation Myocardial Infarction (STEMI), for blood troponin level (high or low) and for new onset or recurrent onset AMI. The STEMI and NSTEMI were classified by the presence or absence of ST-elevation finding in ECG. High-troponin was defined as the upper 4th quartile of the blood cardiac troponin level ≥24.3 ng/mL. STEMI and high-troponin were measures of more severe myocardial damage among AMI cases. The Pearson X2 test was conducted to compare the proportions of CRI and influenza across AMI subgroups. For the differences between groups, a p value ≤0.05 was considered as statistically significant.