Hospitalizations Associated with Pandemic Influenza A (H1N1) 2009 in Asthmatic Children in Japan

Background: The pandemic influenza A (H1N1) 2009 [pdm (H1N1) 2009] spread through the world in 2009, producing a serious epidemic in Japan. Since it was suggested early that asthma is a risk factor for an increased severity of the infection, the Japanese Society of Pediatric Allergy and Clinical Immunology (JSPACI) organized a working group for countermeasures, and investigated asthmatic children admitted to the hospitals for pdm (H1N1) 2009 infection. Methods: An appeal was made on the home page of the JSPACI to medical practitioners to input clinical information about asthmatic and non-asthmatic children (0–19 years) admitted to the hospital with pdm (H1N1) 2009 infection. Results: A total of 862 children (390 with asthma, and 472 without asthma) from 61 medical centers were registered, and the data of 333 asthmatic children and 388 non-asthmatic children in all were entered in the analyses. The mean age was 7.4±2.9 years in the asthma group and 6.9±3.8 years in the non-asthma group. The percentage of children admitted for respiratory symptoms was significantly higher in the asthma group than in the non-asthma group (p