A compendium of causative agents of occupational asthma

The objective is to provide an evidence-based compendium of allergenic and irritant agents that are known to cause occupational asthma in order to improve diagnostics and disease management.

Two previously published reviews from our group utilized database searches to identify studies which were then rated according to the Scottish Intercollegiate Guideline Network (SIGN) grading system. The evidence level for each causative agent or worksite was graded using the Royal College of General Practitioners (RCGP) three-star system.

Approximately 3,000 relevant papers were identified, which covered 372 different causes of allergic and 184 different causes of irritant occupational asthma. The highest level achieved using the SIGN grading system was 2++, indicating a high quality study with a very low risk of confounding or bias and a high probability of a causal relationship. Using the modified RCGP three-star grading system, the strongest evidence of association with an individual agent or worksite ('***') was found for exposure to laboratory animals. Associations with moderate evidence level (‘**’) were obtained for a) the allergenic agents or worksites: alpha-amylase from Aspergillus oryzae, various enzymes from Bacillus subtilis, papain, bakeries, western red cedar, latex, psyllium, storage mites, rat, carmine, egg proteins, Atlantic salmon, fishmeal, Norway lobster, prawn, snow crab, seafood, trout and turbot, reactive dyes, b) the irritant agents or worksites: benzene-1,2,4-tricarboxylic acid, 1,2- anhydride [trimellitic anhydride], chlorine, cobalt, cement, environmental tobacco smoke, grain, welding fumes, construction work, swine confinement, World Trade Center disaster 2001, and c) agents or worksites causing allergic as well as irritant occupational asthma, included farming, poultry confinement, various isocyanates and platinum salts. A low evidence level (RCGP) was obtained for 84 agents or worksites (42 from each group), providing a total of 141 conditions with a low, moderate or strong evidence level.

This work comprises the largest compendium and evaluation of agents and worksites causing allergic or irritant occupational asthma from the literature assessed in an evidence-based manner.