Clinical courses and outcomes of hospitalized adult patients with seasonal influenza in Korea, 2011-2012: Hospital-based Influenza Morbidity & Mortality (HIMM) surveillance

Influenza is an acute respiratory illness, which can be accompanied by complications such as pneumonia. This study was conducted to survey the clinical courses and outcomes of hospitalized adult patients with laboratory-confirmed seasonal influenza. A prospective case-control study was performed in adult influenza patients who were admitted to hospitals participating in the Hospital-based Influenza Morbidity and Mortality (HIMM) surveillance system in Korea from October 2011 to May 2012. Cases with complicated influenza were compared to those without complications. A total of 123 (5.6%) patients among 2184 laboratory-confirmed adult influenza patients were hospitalized during the 2011-2012 influenza epidemic season. Forty (32.5%) experienced 50 complication episodes. Age older than 60 years (P < 0.01), male sex (P = 0.04), diabetes (P < 0.01), chronic cardiovascular disease (P < 0.01) and neuromuscular disease (P = 0.02) were significantly related to development of complications in univariate analysis. Multivariate logistic regression analysis revealed that diabetes (odds ratio [OR] 3.63, 95% confidence interval [CI] 1.15-11.51, P = 0.02) was an independent risk factor for complicated seasonal influenza. C-reactive protein (CRP) was discriminative between complicated and uncomplicated influenza (cutoff value 13 mg/L, sensitivity 70%, specificity 74%). Complicated patients received antibiotics more frequently (P < 0.01) with longer hospital stays (P = 0.01). In conclusion, diabetic patients are at great risk for complicated influenza, and CRP would be useful to predicting complication. Therefore, early interventions such as antiviral therapy should be considered for high risk patients with diabetes, especially those with increased serum CRP level.