Evaluation non invasive de l'inflammation des voies aériennes chez les jeunes travailleurs exposés à des agents inhalés facteurs de risque d'asthme professionnel" Une évaluation prospective comparative de la réponse à la métacholine et du monoxyde d'azote – MIBAP

Background: Airway inflammation is recognized as the basic alteration of occupational asthma. However, little is known about the factors that can affect the development of airway inflammation from the very beginning of exposure to an occupational agent through the onset of symptoms. Objective: The main objectives of this study are: (a) to investigate the early development of airway inflammation and asthma-like symptoms in apprentice bakers and hairdressers – two populations at risk of occupational asthma, and (b) to examine the performances of a battery of tests likely to detect early airway inflammation that might eventually develop into asthma. Two secondary objectives are: (a) to examine the extent to which risk factors such as atopy or cigarette smoking may modulate the effects of causal agents of occupational asthma and (b) examine the association between individual characteristics observed at enrolment and during follow-up and the dropout rate. Subjects and methods: A longitudinal study will be carried out with the follow-up of 900 apprentices - 400 apprentice bakers and 500 apprentice hairdressers - entering career programs at 6 “Centres de Formation d’Apprentis (CFA)” of Meurthe & Moselle, France. Power calculation showed that this sample size is necessary in order (1) to quantify the sensitivity of a test around 70-80% with a precision of 10-15%, or (2) to demonstrate that the sensitivity of a test A is 15% greater than that of a test B, with a power of 80% . Asthma-like symptoms will be assessed by questionnaire and atopy by skin prick tests with common and occupational aeroallergens. Airway inflammation will be assessed by three methods: a) the conventional methacholine challenge test (MCT); b) the measure of exhaled nitric oxide (ENO), and; c) eosinophils count in nasal washings. MCT will be assessed using three indices measured in sequence namely (i) respiratory impedance by the forced oscillation technique (FOT), (ii) forced expiratory parameters by spirometry, and (iii) spectral analysis of lung sounds. In contrast with spirometry, FOT and lung sound analysis are simple, non-invasive, risk free, devoid of discomfort and require only passive co-operation. The subjects will be first examined at apprenticeship Year 1, before any exposure, and at 6, 12 and 18 months follow-up. Significance: Hopefully this work will allow (a) a better understanding of the sequence of inflammatory processes in the preclinical phase of development of occupational asthma due to the agents involved; and (b) the definition of the best procedure, or set of procedures, capable to detect early airway inflammation and asthma in occupational or environmental epidemiology.