Background: An initial epidemiological study carried out 18 years ago in Marseilles indicated that the air quality in schools was poor and that there was an association between the level of fine particulates and the occurrence of asthma in children. The aim of the present study was to evaluate the change in the prevalence of childhood asthma and allergic diseases and their link with the levels of air pollutants and other factors of potential risk. Methods: In 2016, using a questionnaire identical to the one used for the 1st survey in 1998-1999, we collected information regarding the symptoms, the diagnosis, and the potential confounding factors. We measured the main indoor and outdoor pollutants at the schools. Results: Overall, the prevalence of asthma and of allergic diseases exhibited an increasing trend in the time interval between the two studies, significant only for dry cough and pollen allergy. The level of air pollutants decreased significantly indoors. In spite of this, we found a correlation and a dose-effect relationship between the level of PM 2.5 and the prevalence of asthma. A family history of asthma and allergies, the insalubrity of the place of residence, and a non-Mediterranean diet were also associated with the risk of these diseases. Conclusion: In the time interval between the two studies, which were 18 years apart, despite a reduction in the level of air pollutants in classrooms, asthma was still related to PM 2.5. Other potentially causative or contributing environmental factors were also related to asthma and allergies.

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