1 COPSAC, Copenhagen Prospective Studies on Asthma in Childhood, Herlev and Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark.
2 Airway Disease Infection Section, MRC & Asthma UK Centre in Allergic Mechanisms of Asthma, National Heart & Lung Institute, Imperial College London, London, United Kingdom; Centre for Respiratory Infection, National Heart & Lung Institute, Imperial College London, London, United Kingdom.
3 COPSAC, Copenhagen Prospective Studies on Asthma in Childhood, Herlev and Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark. Electronic address: bisgaard@copsac.com.