Infection: friend or foe to the development of asthma?

Of the most common diseases among humans, respiratory infections are important causes of disease and disability in high-income countries 1 and some of the most common causes of death in low-income countries, especially among children 2. Since the late forties and the early fifties, severe bacterial infections have decreased in frequency and severity in industrialized countries. At the same time, allergy and asthma have increased, starting at the same time but especially from the late seventies and eighties. In Norway, an epidemiological study from 85 health districts showed a lifetime prevalence of asthma of 0.4% among schoolchildren 3, whereas in the mid-nineties it was 10–12% 4. In 1966–1971, the risk of acquiring asthma increased by 2.33% compared to 1946–1950 in 15 industrialized countries in Europe 5. Strachan 6 formulated the hygiene hypothesis based upon the finding that children with siblings had fewer allergies than children without, and based this upon the finding that children with siblings had more respiratory infections early in life. Later findings, both epidemiological as well as basic scientific research 6, have supported this hypothesis. However, there are more complex relationships between infections and asthma (and allergy). In this issue of European Respiratory Journal ( ERJ ), a new series of articles highlighting this topic from different points of view and based upon different types of scientific studies, starts with an article by von Mutius 7, taking up the epidemiological part of this problem. von Mutius 7 gives an impressive review of the existing epidemiological evidence. Respiratory syncytial virus (RSV) is the most frequent cause of acute bronchiolitis and lower respiratory tract disease during …