Occupational asthma in an electronics factory: a case control study to evaluate aetiological factors

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Abstract
Occupational asthma due to sensitivity to colophony fumes (a component of soldering flux) in an electronics factory was investigated. Workers (58) with occupational asthma employed on the main shop floor were investigated. The interval between 1st exposure and sensitization varied widely with a group becoming sensitive within 1-2 yr of 1st exposure and another group whose sensitization was delayed for 3-23 yr. Once sensitized the interval between arrival at work and the onset of daily symptoms seemed bimodally distributed, resembling the immediate and late asthmatic symptoms seen on provocation testing. Of 58, 23 workers had no definite daily deterioration at work but improved during the weekends. Wheeze and breathlessness occurred in the evenings at home in most, and 1/3 were woken by breathlessness at least on some nights. These 58 cases were compared with 48 controls without occupational asthma who worked on the same shop floor for at least 4 yr. Mean levels of FEV1 [forced expiratory volume in 1 s] were significantly worse in the cases before exposure on Monday morning. The cases also had more than twice as much sickness absence as controls. FEV1 fell by more than 10% over a working shift in 33% of cases and 5% of controls. Atopy (a positive skin prick test to 1 or more common allergens) and a past history of allergic disease were weakly but significantly associated with being a case. The effects of smoking and a family history of allergic disease were trivial. Prick testing with an antigen derived from the colophony in the solder flux was completely negative, but cases and controls had significantly raised levels of total Ig[immunoglobulin]M compared with blood bank controls, perhaps suggesting some previously unrecognized immunological process.

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