Fewer colds, less asthma? A hypothesis to explain the fall in childhood asthma in the UK.

UK asthma prevalence fell significantly between 1993 and 2000. In children aged <5 years hospital admissions for asthma fell by 52% and primary care presentations in children under 14 years by over 40%. From 1994 to 2000, primary care consultations for acute respiratory infections in all age groups fell by 36%, and for the common cold by 46%. Isolates for respiratory syncytial virus notified to the Health Protection Agency voluntary reporting scheme fell by 56% between 1993 and 2003. Falls in UK birth rate and improvements in living conditions were reported by the Office of National Statistics over this time. The authors hypothesise that the fall in asthma reflects a fall in respiratory infections, the most important proximal trigger for asthma exacerbations, and that this in turn may be related to a fall in household members to a number too low for effective virus transmission. Future research into the prevalence of asthma must consider the effect of changing respiratory virus burden on populations.