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Baker's asthma

2002; BMJ; Volume: 59; Issue: 7 Linguagem: Inglês

10.1136/oem.59.7.498

1470-7926

Jonas Brisman,

Indoor Air Quality and Microbial Exposure

aker's asthma is one of the most common forms of occupational asthma.The increasing knowledge in exposure-response relations accumulated in recent years is important in the understanding of baker's asthma.This development has made scientifically based prevention feasible today and baker's asthma should not be regarded as an inevitable occurrence any more.In 1700 Bernardo Ramazzini described respiratory symptoms among bakers caused by exposure to flour dust.However, there are anecdotal references from antiquity describing how Roman slaves working in bakeries protected themselves by using cloth as a primitive respirator to cover their faces because their breathing suffered from inhaling flour. c CLINICAL PICTURECase reports from the beginning of the 20th century established the concept of baker's asthma as an allergic disease because of the observed combination of positive skin tests to flour extracts and respiratory symptoms suggestive of asthma.The aetiological role of sensitisation to flour in these cases was confirmed by bronchial challenge tests.Rhinitis is very common and usually precedes asthma.Conjunctivitis and skin symptoms may also occur.The baker is often atopic by skin or IgE tests.Symptoms develop after a latency period of months or years, even decades.Initially there is often a clear temporal relation between symptoms and periods of bakery work.Over time, respiratory symptoms may cease to resolve during time off from the bakery.Sensitisation to flour is traditionally often regarded as a prerequisite for the diagnosis of baker's asthma.Although the prognosis of baker's asthma is not reported in the literature, it is usually presumed that symptoms resolve if exposure to offending allergens is stopped. EPIDEMIOLOGYFrom the 1930s onward there was a number of cross sectional studies surveying populations of bakers, unfortunately many of them uncontrolled-that is, without comparing the bakers with controls.These studies varied considerably in the description of symptoms, and in the definitions of asthma and sensitisation.Also exposure to bakery dust varied across the studies.Although epidemiologically crude by today's standards, they showed that bakers have more lower respiratory tract symptoms, sometimes labelled as asthma and considered as "normal", but also nasal symptoms, indicating baker's rhinitis. 1Positive skin tests to flour were found not only among those with asthmatic symptoms but also among bakers with rhinitis or even among those without symptoms ("latent allergy").The presence of flour allergy was usually included in the definition of Baker's asthma in the clinical setting.The earlier findings from the case series of an association between baker's asthma and atopy were corroborated in the cross sectional studies.There are a few longitudinal studies estimating the incidence of respiratory symptoms and sensitisation to bakery allergens.Gadborg studied Danish bakers and published his results in 1956.He made a follow up of 487 out of 500 randomly selected bakers after 5-6 years.The incidence rate for sensitisation to flour was about 5.5 cases per 1000 person years, and for baker's asthma (symptoms and sensitisation) about 1.5.An often cited German study of bakers' apprentices by Herxheimer showed a cumulative incidence for sensitisation of 19% and 7% for respiratory symptoms after three years.As only one third of the original cohort were studied at that time point, the interpretation of the results is difficult.A Swedish retrospective study of trainee bakers showed male incidence rates for asthma of 3.0 cases per 1000 person-years (referents 0.9-1.9),and for rhinitis 29.4 cases per 1000 person-years (referents 10.1-11.1). 2 3 A cohort of 300 newly employed UK bakers and millers was followed for a maximum of seven years. 4 The incidence rates of work related chest symptoms was 41 per 1000 person-years, of work related eyes/nose symptoms 118 per 1000 person-years, of sensitisation to flour 22 per 1000 person-years, and of sensitisation to the enzyme fungal α amylase 25 per 1000 person-years.The incidence of work related chest symptoms and a positive skin prick test to flour or fungal α amylase was about 10 per 1000 person-years.