Evaluating the Risk of Viral Myocarditis following Influenza Infection among Hospitalized Patients during 2014–2015 and 2015–2016 Influenza Seasons

Abstract Background Myocarditis is a severe cardiovascular complication of influenza infection that is often fatal and underdiagnosed. We evaluated the epidemiology of influenza myocarditis (IM) among inpatients at one institution. Methods We performed a retrospective cohort study of inpatients harboring influenza virus by reverse transcription-polymerase chain reaction from respiratory specimens between 2014 and 2016. We collected demographic, treatment, strain-typing, and hospitalization data for all patients. Definitive IM was proven by histopathology or viral isolation from myocardial tissue. Probable and possible IM were based on CDC and predefined clinical criteria, respectively. We used the chi-squared test to compare characteristics between 2014–2015 and 2015–2016 influenza seasons and the subset of patients with cardiovascular complications. Results We identified 757 patients with influenza in 2014–2015 (n = 453) and 2015–2016 (n = 304). Baseline characteristics including gender, influenza type, and co-morbidities were similar between seasons except for more white and cardiovascular disease (P