Evolution of work related asthma in France over the period 2001-2009

Introduction
Work-related asthma (WRA) is one of the most common occupational lung diseases in many industrialized countries. However, knowledge on temporal evolution (trends) of this disease remains sparse. Moreover, there is a need to adapt statistical methods for trend analyses in occupational health surveillance system. The aim of the study was to compare several statistical methods of temporal evolution and apply these approaches to main trends of WRA in France over the period 2001-2009.

Methods
Data have been collected from the French national network of occupational disease surveillance and prevention [Réseau National de Vigilance et de Prévention des Pathologies Professionnelles (RNV3P)]. Several statistical methods (non parametric test, zero-inflated negative binomial (ZINB), logistic regression (Reporting Odds Ratio) and time-series models) were used and compared to assess the trends.

Results
Comparisons of methods demonstrated satisfactory correlations between ZINB and logistic regression models. Over the 2914 cases included in this study, a significant decrease was observed overall and for some agents like isocyanates (12.7% in 2001 to 6.2% in 2009 of all WRA cases, p=0.007), aldehydes (6.8% to 1.6% respectively, p=0.01) and latex (5.4% to 2.5 respectively, p=0.01). Conversely, a significant increase was observed for cases in relation with quaternary ammonium compound exposure (1.4% in 2001 to 8.3% in 2009 of WRA cases, p=0.003). The health and social sector demonstrated a rising of cases in relation with the use of ammonium quaternary compounds and a decrease of cases associated with aldehydes and latex exposure.

Discussion
Overall, WRA declined in France over the studied period. WRA associated with ammonium quaternary compound exposure were the only situation with a significant increase. ZINB and logistic regression models seem to describe adequately the data.