Background/Purpose: This prospective study aimed to describe the clinical features, as well as outcomes, of adult patients with influenza of different severity, and to determine the predictors for development of complications. Methods: From December 2006 to March 2009, four types of diagnostic tests were given to both in- and outpatients with influenza-like illness (ILI). Confirmed cases were categorized into three groups (uncomplicated, moderately complicated, and severely complicated) for analysis using a proportional odds logistic regression model. Results: A total of 206 laboratory-confirmed cases of influenza were identified out of 360 enrolled patients with ILI. Among 30 patients (14.6%) classified as complicated cases due to development of pneumonia (n=28) and viral encephalopathy (n=2), 16 were hospitalized in general wards (moderately complicated) and 14 required admission to intensive care units (severely complicated). Complicated patients were less likely to have classic symptoms of ILI than uncomplicated patients. By multivariate analysis, the presence of coronary artery disease, systemic corticosteroid use, impaired renal function and delayed hospital visit were independently associated with development of complications. Conclusion: Our study results may help clinicians to identify patients at high risk for complicated influenza, to provide timely antiviral therapy and optimal clinical care.
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