Heart failure among patients admitted with Influenza. The influenza subtypes, seasonality and mortality

Respiratory infections like influenza infections have been found to increase the risk of coronary artery disease and precipitate cardiac failure. However, Indian data is lacking. A retrospective observational study was done to describe patients with influenza infection who had concomitant heart failure (HF) requiring admission over 5 years (January 2013-December 2017). A total of 93 influenza cases were hospitalised during this time, of which 14 (15%) also had features of HF. Among them, the types of influenza infection were AH1N1 (6,43%), BH1N1 (4,29%), AH3N2 (3,21%) with one patient having both strains. Two-thirds of the HF were new onset (10, 71%), whereas rest were due to acute worsening of pre-existing HF (4, 29%). Ten (64.3%) of the patients had HF with reduced ejection fraction (HFrEF). The average hospital stay was 10 days with 2 (14%) deaths. The peak of influenza in August and September preceded the peak admission for HF. A total of 15% of influenza admissions have concomitant HF. They are predominantly due to influenza A H1N1 (43%), influenza A H3N2 (21%) and influenza B (29%). Only 7% had preceding influenza vaccination. Influenza during August and September appears to precede the peak of HF admissions which happen in October and November. Overall mortality was 14.