Atopic and non-atopic asthma in a farming and a general population

BACKGROUND: In a previous study inverse associations between asthma and exposure to fungal spores and endotoxins in atopic farmers and positive associations with the same factors in non-atopic farmers were documented. No external reference population had been included. We, therefore, compared this farming population with the general population from an adjacent region. METHODS: Random samples of a farming (n=2,106) and a rural (n=351) and urban (n=727) general population were selected. Atopy was assessed by serum IgE and asthma by questionnaires. RESULTS: The asthma prevalence was 4.0% among farmers, 5.7% in the rural, and 7.6% in the urban population. Atopy was similar (9-10%). Most asthmatics were not atopic, 67-75%. Farmers had asthma less often than the general population OR 0.52 (95% CI 0.36-0.75); both atopic (OR 0.33 (95% CI 0.15-0.69)) and non-atopic asthma (OR 0.60 (95% CI 0.39-0.93)). CONCLUSION: This may indicate a protective effect of the farm environment on asthma but a healthy worker effect may also play a role.