Cardiovascular complications due to viral infection pose a significant risk in vulnerable patients such as those with congenital heart disease (CHD). Limited data exists regarding the incidence of influenza and its impact on cardiovascular outcomes among this specific patient population.

A retrospective cohort study was designed using the Canadian Congenital Heart Disease (CanCHD) database—a pan-Canadian database of CHD patients with up to 35 years of follow-up. CHD patients aged 40 to 65 years with influenza virus-associated hospitalizations between 2010 and 2017 were identified and 1:1 matched with CHD patients with limb fracture hospitalizations on age and calendar time. Our primary endpoint was cardiovascular complications: heart failure, acute myocardial infarction, atrial arrhythmia, ventricular arrhythmia, heart block, myocarditis, and pericarditis.

Of the 303 patients identified with incident influenza virus-associated hospitalizations, 255 were matched to 255 patients with limb fracture hospitalizations. Patients with influenza virus-related hospitalizations showed significantly higher cumulative probability of cardiovascular complications at 1 year (0.16 vs. 0.03) and 5 years (0.33 vs. 0.15) compared to patients hospitalized with bone fracture. Time-dependent hazard function modeling demonstrated a significantly higher risk of cardiovascular complications within 9 months postdischarge for influenza-related hospitalizations. This association was confirmed by Cox regression model (average hazard ratio throughout follow-up: 2.48; 95% CI: 1.59-3.84).

This pan-Canadian cohort study of adults with CHD demonstrated an association between influenza virus-related hospitalization and risk of cardiovascular complications during the 9 months post discharge. This data is essential in planning surveillance strategies to mitigate adverse outcomes and provides insights into interpreting complication rates of other emerging pathogens, such as COVID-19.