1. First Department of Medicine and
2. Department of Otolaryngology–Head and Neck Surgery, Hokkaido University School of Medicine, Sapporo, Japan
3. Department of Respiratory Medicine, Japan Railways Sapporo Hospital, Sapporo, Japan
4. Department of Respiratory Medicine, KKR Sapporo Medical Center, Sapporo, Japan
5. Department of Respiratory Medicine, Otaru Kyokai Hospital, Otaru, Japan
6. Department of Respiratory Medicine, Oji General Hospital, Tomakomai, Japan
7. Department of Biostatistics, Hokkaido University Graduate School of Medicine, Sapporo, Japan; and
8. University of Pittsburgh Asthma Institute at University of Pittsburgh Medial Center/University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania