ABSTRACT
<b>Introduction</b> : To clarify clinical features of influenza A (H1N1) pdm09, we analyzed patients admitted during the early stage of the pandemic.<br><b>Methods</b> : Analysis covered pediatric patients hospitalized with this virus during the first 3 months of the pandemic.<br><b>Results</b> : The patients (average age, 7.7 years) were older than those in previous analyses and were divided by the reason for admission. The group with respiratory complaints (39 patients) accounted for 40%, in contrast to 10% observed previously, and had a significantly high prevalence of bronchial asthma history (21 patients). Nine patients with dyspnea symptoms preceding fever experienced a shorter period (1.6 days) from onset to admission. These patients had elevated WBC counts (13644/µL) and longer hospitalization (6.0 days). Twenty-nine patients had false negative results in the initial rapid influenza diagnostic tests (RIDTs). Many of them belonged to the respiratory complaints group (20 patients) and developed pneumonia (15 patients). These patients required treatment other than that with anti-viral agents, e.g., oxygen therapy (18 patients), leading to longer hospitalization (4.5 days).<br><b>Conclusion</b> : During the first 3 months of the pandemic, many patients were admitted with respiratory complaints. They had a high prevalence of bronchial asthma history. Patients with dyspnea symptoms preceding fever and those who were initially RIDT-negative required advanced treatments, resulting in longer hospitalization.