 The study group will include inpatients older than 18 years, who have clinical presentation suggestive of influenza virus infection defined by the World Health Organization and the Center for Disease Control and Prevention, including sudden onset of high fever, cough, headache, muscle and joint pain, severe malaise, sore throat and runny nose, who were found positive to influenza virus by polymerase chain reaction test, and in whom anti viral treatment was indicated. 