In April 2009, confirmed cases of influenza A (H1N1) infections were reported worldwide, spreading from Mexico and southern California. In order to determine the clinical features of patients infected with this virus before vaccine implementation and evaluate the response of antiviral treatment in Taiwan, we reviewed medical charts and collected clinical data from outpatients and inpatients at the Tao-Yuan General Hospital.From May 19, 2009, to October 31, 2009, clinical data from patients confirmed by the rapid antigen-screening test for influenza A virus and/or reverse transcriptase–polymerase chain reaction analysis at the Tao-Yuan General Hospital were reviewed retrospectively.A total of 1158 patients (94.6%) received outpatient management, 66 patients (5.4%) were hospitalized, and no patients died. More than two-thirds of patients were younger than 16 years old. The most common symptoms were fever (99.8%), cough (91.4%), sore throat (63.7%), and rhinorrhea (53.8%). Ninety patients (13.3%) had complications, including lower respiratory tract infections (11.1%). Among the 677 patients receiving follow-ups, none needed mechanical ventilation due to lower respiratory tract infection. Most of the patients (87.2%) began antiviral therapy within 2 days after the onset of symptoms. Ninety percent of patients became afebrile within 2 days after the initiation of antiviral therapy. The number of screening specimens and the positivity rate of the rapid influenza A antigen test were dramatically decreased 4 weeks later, after universal implementation of the pandemic influenza A (H1N1) 2009 vaccine to infants and school-age children.The clinical spectrum of pandemic influenza A (H1N1) 2009 infection was broad and the severity of disease was mild. Early antiviral treatment was effective in decreasing mortality and morbidity. Early and universal implementation of a novel influenza A vaccine is an effective approach for preventing pandemic community influenza outbreaks, particularly among infants and school-age children.
