[Is there an urban factor in asthma and allergy?]

To evaluate if an "urban factor" could be responsible for an increase of asthma and allergic diseases in developed countries, we compared prevalence rates for these conditions in adults living in urban and rural settings. The urban group consisted of 4,008 adults, randomly selected from the 16 districts of the city of Marseille; the rural group consisted of 1,789 adults, representing 85% of the target population living in a small residential town, Trets. The protocol included, after a mass media information, home-visits by public health physicians. These physicians asked a short standardized questionnaire to all adults 18 to 65 years old. Then, in a subgroup of, hay-fever patients, they performed skin tests to grass pollens. The standardized prevalence rates of asthma and related symptoms, and hay fever, was very similar in both settings. Thus, this study does not support the hypothesis that there is a urban factor in asthma and allergic diseases. In the literature, several studies point out a higher prevalence of these diseases in an urban setting. But these studies have been performed several years ago, when there was a larger difference in air pollutants concentrations between urban and rural settings.