THE seemingly relentless rise in asthma levels worldwide that has intrigued and infuriated researchers for decades seems to be abating.
Thirty years ago asthma was a rare disease, but round the world the incidence of asthma has gone up by about 50 per cent every decade. Today 100 to 150 million people have the breathing problem, which costs $6 billion a year in the US alone.
But European studies are beginning to hint that the rise in asthma cases may have stopped. A recent study of school children in Rome showed that asthma levels are levelling out for those born after 1985. And a new study presented at the European Respiratory Society鈥檚 Annual Congress in Stockholm this week suggests that this happened at least five years earlier in Switzerland.
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Charlott Braun-Fahrl盲nder and her team at Basel University studied groups of 15-year-old children in Swiss schools in 1992, 1996 and 2000. Parents answered questions on asthma symptoms and on known risk factors in the home 鈥� such as pets and wall-to-wall carpets. The number of patients with persistent asthma stayed at around 8 per cent throughout the 1990s, with little change in any of the risk factors they asked about.
The results are the first to indicate asthma rates are stabilising in children born before 1980, though they still don鈥檛 know why this should be so.
Many environmental factors, such as dust mites and tobacco smoke, are well known triggers for asthma. And new factors continue to be pinpointed. At the same conference, other researchers reported that exposure to antibiotics and high pollen levels while in the womb are associated with increased asthma rates. But no one has tracked down the link between such factors and the global trends.
Mike Silverman, an asthma researcher in Britain, thinks the new research might be particularly valuable in working this out. Comparing living conditions in Switzerland with other countries where the drop in asthma is taking longer to kick in could help researchers pin down the reasons asthma rates rose in the first place, he says.