Rationale and objectives Compost workers have more airway irritation symptoms and increased inflammation markers than non-exposed workers. We studied which activities and processed wastes are involved.

Methods 90 compost workers were followed-up for 18 months with a medical examination every 6 months. At each visit, two questionnaires on the preceding six-months, regarding the tasks of a typical work-week and respiratory health and irritation symptoms, were administered. Fractional exhaled nitric oxide (NOe) measures, spirometry and a methacholine challenge test (MCT) were performed. Skin prick-tests for common aeroallergens were performed on the first visit, and immunoglobulin (Ig) E and G specific to airborne microorganisms commonly observed in composting plants were quantified on two visits.

Results Sixty-one subjects (68%) worked in 20 green waste (GW) plants and 29 (32%) in 15 sewage sludge (SS) plants. Thirteen workers (14%) were drivers or mechanics considered as having low exposure. Thirty-seven workers were atopic (42%) and 12 (13%) had ever-asthma. Workers in plants processing the highest quantities of waste had more upper (OR = 7.5, IC95%=[1.3;42.7]) and lower (OR = 1.05, IC95%=[1.0;1.1]) airway irritation symptoms and digestive symptoms (OR = 1.23, IC95%=[1.0;1.5]), and more frequently altered FVC (OR = 1.3, IC95%=[1,1;1,5]) and FEV1 (OR = 1.2, IC95%=[1.0;1.4]). Mixing materials (OR = 1.04, IC95%=[1.0;1.1]) and handling compost (OR = 1.13, IC95%=[1.0;1;2]) were tasks associated with more asthma-like symptoms. Cleaning activities were associated with a higher MCT dose-response slope (β = −0.010, IC95%=[−0.019;−0.001]). Workers in GW plants had a higher risk of having an increased NOe than workers in SS plants (OR = 45.8, IC95%=[2.6;808.2]). Less exposed workers had a lower level of IgE specific to actinomycetes (exp(β)=1.17, IC95%=[1.04;1.32]).

Conclusion This is the first time the characteristics of the plants, tasks performed and types of waste processed have been linked to markers of airway inflammation and symptoms in compost workers.