Influence of Influenza Infection on In-Hospital Acute Myocardial Infarction Outcomes

Influenza is associated with significant morbidity in the United States but its influence on in-hospital outcomes in patients with AMI has not been well studied. The Nationwide Readmission Database (NRD) from 2010 to 2014 was queried using the International Classification of Diseases-Ninth edition, Clinical Modification (ICD-9-CM) codes to identify all patients ≥18 years who were admitted for AMI with and without concurrent influenza. Propensity score matching was used to adjust patients' baseline characteristics and co-morbidities. In-hospital mortality, 30-day readmission rates, in-hospital complications, and resource utilization were analyzed. We identified a total of 2,428,361 patients admitted with AMI, of whom 3,006 (0.12%) had coexisting influenza. We noted significantly higher in-hospital mortality (7.7% vs 5.6%, p <0.01) and 30-day readmission rates (15.8% vs 14.1%, p <0.01) in patients with influenza compared with those without it. After propensity matching, the differences in in-hospital mortality and 30-day readmission were no longer statistically significant between the groups. Patients with influenza had a higher incidence of acute kidney injury (30.9% vs 24.6%, p <0.01), acute respiratory failure (50.2% vs 32.2%, p <0.01), need for mechanical ventilation (13.9% vs 9.2%, p <0.01), and sepsis (10% vs 3.8%, p <0.01) in the matched cohort. Patients with influenza had longer hospital stays (8.4 days vs 6.4 days, p <0.01) and mean costs of care (26,200USD vs 23,400USD, p <0.01). In conclusion, AMI patients with concomitant influenza infection had higher in-hospital mortality, 30-day readmission, in-hospital complications, and higher resource utilization compared with those without influenza.