BackgroundOver 400 agents are known respiratory sensitisers and thus may cause occupational asthma. A man who produced nematodes for horticultural purposes presented with rhinoconjunctivitis and asthma symptoms occurring only on days at work when exposed to Steinernema feltiae.AimTo determine if he had occupational asthma to S.feltiae.MethodsA specific provocation inhalation test was performed using a suspension of S.feltiae in water nebulised into an exposure chamber. We used a single-blind method with saline as an inert control; three exposures (two active) took place on separate days. Symptoms, FEV₁ and, 24 hours after each challenge, response to inhaled histamine were monitored. At baseline, FEV₁ was 4.25 L/min and his histamine PC20 11 mg/ml.ResultsExposure to saline alone induced no symptoms and no change in spirometry or histamine responsiveness. Exposure to S.feltiae on two separate occasions induced early and late reductions in FEV₁ (nadir of 2.98 L/min) with a decrease in histamine PC20 to 1mg/ml and reproduced symptoms experienced at work. (figure 1)

A bespoke specific IgE assay against S.feltiae was positive (4.1% binding) in a serum sample.ConclusionElucidating the precise cause of occupational asthma is not always straightforward and may involve complex tests but is important. We confirmed occupational asthma and rhinitis due to S.feltiae, with implications for this patient and for the manufacturers and biological pest controls users.