Respiratory hazards in dairy and beef farming

A joint Health and Safety Executive (HSE): Institute of Occupational Medicine (IOM) study of respiratory hazards in dairy and beef farming was conducted in 1993 and 1994 as a preliminary to a proposed HSE Technical Development Project. The study combined the development of exposure assessment methods and the design and validation of a respiratory symptoms questionnaire in the context of dairy and beef farming. Clinical examinations of farm workers were undertaken and blood samples were analysed. Patterns of exposure of farmers and farm workers were observed and some measurements of airborne dust and microorganisms were made. Practical methods of controlling exposure were identified.The study was undertaken in two phases. In the first phase, a total of 26 dairy and beef farms were visited. A purpose-designed questionnaire on respiratory symptoms, smoking and occupational history was administered to all full time farm workers who had been working on the farm for more than 12 months. The questionnaire was designed to identify, as far as possible, the common respiratory syndromes which may be associated with work on farms. Supplementary questions about the association of symptoms with the time, place, and specific agents were included and found to be informative. Clinical investigations of selected cases with respiratory syndromes and controls were undertaken. These allowed the sensitivity and specificity of the questionnaire to be determined. The study found the questionnaire to have an overall sensitivity, for the identification of defined respiratory syndromes, of 57% and a specificity of 95%. In general, the estimated frequency of respiratory disease amongst dairy and beef farm workers was high. This included a high frequency of occupational rhinitis, asthma and occupational asthma. Chronic bronchitis was relatively infrequent. There was no recent evidence of extrinsic allergic alveolitis or organic dust toxic syndrome, although some cases of the former occurring in earlier years were identified.The Respiratory Symptoms Questionnaire appeared to be a reasonably adequate tool for the purpose of identifying respiratory syndromes. Its specificity is high, though moderate sensitivity indicates that it provides a fairly secure estimate of a lower limit of frequency and case identification. Further investigation of other combinations of questionnaire answers might enable improvement of sensitivity of the questionnaire without important loss of specificity.Information was also gathered during the first phase, on which tasks were undertaken at each farm, the nature of the work involved, the substances encountered and the frequency and duration of each task. This was used to develop a Hazard Identification Form which provides a structured basis for recording this information in a suitable format for data collation. Although the main purpose of the form is hazard identification, short descriptions of the tasks can be used to give reliminary estimates of exposure intensities and durations.The second phase of the study was used to develop further the exposure assessment methodology. A form was developed to enable systematic collection of details about each task to be collected. This information provides the basis for an expert judgement of the intensity of exposure to be made. The Exposure Assessment Form was tested and refined at six of the original farms during the second phase of the study. Total inhalahle dust and microorganism concentrations were also measured. The preparation of feed, distribution of feed and bedding of cattle housing generated substantial quantities of dust and bioaerosols. Only tasks performed during the winter months were available for monitoring; some tasks performed only in the summer, for example harvesting and haymaking, are also expected to produce significant dust and bioaerosol concentrations.The patterns of tasks and exposure in beef and diary farms are complex. Similar tasks were carried out on all of the farms but different methods and materials were used. Task frequency and duration were also variable.A number of practical methods of controlling exposure were encountered. Most involved modification of working practices or a change of substance, rather than the implementation of engineering controls.The study has been undertaken in preparation for a larger HSE Technical Development Project. The Hazard Identification and Exposure Assessment Forms and the Respiratory Symptoms Questionnaire will be powerful tools in the Technical Development Project. Care will, however, be necessary to ensure that they are applied and administered consistently throughout the study as inconsistencies could result in spurious findings or in real effects being missed. Comprehensive training and some form of ongoing performance review will be essential. A structured approach to exposure assessment will also help. Exposure measurements are time-consuming and expensive. They should be primarily used to scale and validate the exposure assessments made using the Exposure Assessment Forms. Furthermore, these exposure assessments cannot be made for all tasks at all farms and only the very limited information on exposure intensity collected using the Hazard Identification Forms will be available for many tasks. The value of this information should be assessed by comparison with formal exposure assessments. This type of intercomparison and validation, if undertaken in the early stages of the project, should aid the efficient collection of exposure information.