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To the Editor:
With dairy and crop farming being the largest sectors, agriculture and horticulture provide employment approximately for 100,000 people in Finland. Agriculture workers have a high risk for exposure to respiratory hazards. Because only a small portion of the overall population is employed in agriculture, respiratory disease in farmers is not a major public health issue. Despite this, the health and well-being of farmers as well as their health risk reduction in their working conditions needs to be examined, especially because a farming environment has been thought to prevent the development of allergies.1 Respiratory diseases and symptoms are well-recognized occupational problems among farmers.2 Agricultural workers in all sectors of farming are exposed to various types of airborne toxins and allergens in their work, including organic dust, pesticides, and microbes.3 Several different types of gases (eg, ammonia, methane, and carbon dioxide) may also be present in their working environments. Inhalation of biological dusts, which are composed of organic material from straw, hay, animals, and microbes, can cause changes in pulmonary function, induce antibody formation and lead to the development of respiratory disease. Several studies have indicated a higher prevalence of respiratory symptoms among agricultural workers.4,5
Research about respiratory symptoms and diseases in Finnish farmers during the past decades is scarce. Therefore, this letter is intended to draw attention to the respiratory health issues of agricultural workers. In our research project, we compared the current prevalence and occurrence trends of self-reported respiratory symptoms and disorders in different Finnish agricultural sectors and determined risk factors in the development of the symptoms. Determining these risk factors can improve health recommendations and other preventive actions. The Farmers’ Social Insurance Institution (MELA) e-mailed the questionnaire to 10,000 of its members selected by simple random sampling with the final response rate being 25.1%. The questionnaire sought to obtain information about work history, work conditions, and several symptoms, including respiratory symptoms. It was formulated by the discipline of Occupational Health at the University of Turku and based on the questionnaire used in the occupational health project of Finnish farmers project6 including also the Örebro questionnaire and adequate parts of the Tuohilampi questionnaire.7
ANIMAL RELATED EXPOSURES: A MAJOR CAUSE FOR THE CURRENT PREVALENCE OF RESPIRATORY DISORDERS AMONG FINNISH FARMERS
The mean age of farmers ranged from 47.1 to 52.4 years. The study population in the farming sectors were different in their sex and age distributions (P < 0.001). The prevalence of young farmers was significantly lower in each farming sector. The description of the study population is presented in the Table 1. Farmers working with animals reported more respiratory symptoms than farmers working in haying, crop farming, or forestry (Table 2). Dairy farmers reported more complaints about a stuffed nose, rhinitis, and dyspnea during physical strain than all other farmers. Purulent rhinitis, sore throat, hoarseness, and dry cough were associated with pig farming. A significant elevation was also observed in “tightness of breath,” which was associated with dairy and pig farming. Farmers working in haying reported less often a stuffed nose, rhinitis, purulent rhinitis, dry cough, phlegm, dyspnea in physical strain, and tightness of breath than other farmers. Crop farming had a negative association with the prevalence of stuffed nose and dry cough. Forestry workers reported less often a stuffed nose but had an elevated level of phlegm compared with other farmers.
Table 3 shows the prevalence of wheezing and respiratory diseases categorized by farming exposure factors. Exposure to cattle showed an increase in the prevalence of chronic bronchitis but otherwise animal exposure was not associated with an increase in the respiratory diseases. However, exposure to animal excrement and fodder was associated with an elevated prevalence of wheezing and chronic bronchitis. Those workers, who were exposed to animal fodder, also showed an increased prevalence of asthma. Organic dust exposure was associated significantly with a higher prevalence of wheezing, asthma, allergic rhinitis, and allergic alveolitis. The usage of respiratory protective equipment was varied. Two out of three pig farmers reported that they used a respirator mask. However, among dairy and beef farmers the numbers were 34.7% and 37.8%, respectively. The usage of a respirator mask was reported by 57.8% of hay-, 56.3% of crop-, and 26.1% of forestry farmers.
Several factors can affect the quality of air in occupational environments. These factors include humidity, temperature, ventilation, dirt, material emissions, and moisture damages. Dampness and moisture problems can also lead to the growth of molds, bacteria, and rot fungi, which can expose building users to several emissions in the indoor air. The symptoms in this study seemed to be linked to heavy exposures of organic dust derived from various sources. Of all the farming sectors, pig farmers had the highest prevalence of work-related respiratory symptoms, and insufficient ventilation was reported more likely by dairy-, pig-, and beef farmers than by farmers in other farming sectors. These findings are consistent with previous research conducted in Europe.8 Working in these production fields requires a high-intensity exposure to barn air. The barn air is a mixture of dusts, gases, and organic substances (eg, methane, hydrogen sulfide, ammonia, endotoxin, etc) and is known to cause lung dysfunction and to be a major risk factor for respiratory symptoms.9,10 In barns containing swine, this barn air has been demonstrated to increase the bronchial responsiveness and levels of neutrophils as well as several proinflammatory factors in the serum in naïve, healthy volunteers.11
FARMERS DEVELOP ASTHMA EQUALLY COMPARED WITH GENERAL POPULATION
The overall prevalence of doctor-diagnosed asthma was 10.8% in the farmers but was higher for crop farmers (13.1%), pig farmers (12.0%), cattle farmers (11.9%), and dairy farmers (11.4%). However, the differences among different farming types were not significant. Doctor-diagnosed allergic rhinitis was reported by 12.3% of the farmers overall but was found somewhat higher in crop farmers (14.6%). Doctor-diagnosed allergic alveolitis (ie, hypersensitivity pneumonitis) was reported by 1.2% of the farmers overall with the numbers being fairly similar in all farming sectors, except in forestry, where there were no cases reported. The respondent was classified as having chronic bronchitis if he or she had coughed up phlegm for at least 3 months annually for at least 2 consecutive years. The overall prevalence of chronic bronchitis was 21.4% but was lower in the farmers who worked in haying or crop farming (16.3% and 17.2%, respectively, P < 0.05).
We assessed the independent effect of the work-related exposures on the development of respiratory disorders by adjusting the farming categories by the age, sex, and smoking. Farmers working with cattle had an elevated risk to chronic bronchitis compared with all other farmers (OR 1.44, 1.12 to 1.84). Disinfection and cleaning chemical exposure elevated the risk for wheezing (OR 1.78, 1.17 to 2.70) and chronic bronchitis (OR 1.31, 1.03 to 1.68). Elevation in the risk for asthma was observed in workers, who had exposure to fodder (OR 1.49, 1.09 to 2.04) and organic dust (OR 1.85, 1.39 to 2.46). The latter also elevated the risk for wheezing (OR 2.41, 1.60 to 3.63), allergic rhinitis (OR 1.77, 1.36 to 2.31), allergic alveoltis (OR 8.95, 3.04 to 26.4) and chronic bronchitis (OR 1.84, 1.46 to 2.32).
The published data about the association between farmers and asthma are conflicting. Previous research has shown a lower prevalence of the development of asthma and allergies among farmers,12 but there are also findings suggesting that the highest risk of asthma, when analyzed by occupation, is among agricultural workers.13 Among children who grow up on a farm, studies have drawn attention to the possible protective effect of a farming environment for these children against atopy and asthma.14,15 An important question is whether the protective effect persists into adulthood. According to our study, adult farmers developed asthma equally compared with the general population. Importantly, the proportion of farming as an occupation in Finland has declined considerably after the Second World War. Before the 1940's, about 60% of the Finnish population followed this occupation and now less than 10% do. In the early 1980s, asthma was diagnosed only in 2% to 3% and chronic bronchitis in 5% of Finnish farmers.6,16,17 In the early 1990s, the prevalence of asthma among Finnish farmers had raised to 4.4%. The trend in the increase of diagnosed asthma among farmers seems to follow the development of asthma in the Finnish population during the recent decades.18,19 In this study, asthma was associated with microbial exposure and fodder handling. Previous research has associated asthma and pig farming due to possible causes such as organic dusts, endotoxins, ammonia, and bacteria.10
An increased prevalence of both allergic rhinitis and allergic alveolitis were associated with exposure to organic dust in the work environment. The overall prevalence of allergic rhinitis (12.3%) in farmers was lower than in the Finnish population being 28.1% in men and 36.1% in women.19 Previous studies have shown similar results with a prevalence of self-reported nasal allergies among farmers being lower than estimates in the general population.5,20 Extrinsic allergic alveolitis (also called hypersensitivity pneumonitis) often results from recurrent exposure to microorganisms present in moldy plant materials.21 In a meta-analysis carried out by Guillien et al,22 an increased prevalence of chronic bronchitis was found in farmers raising cattle, swine, and poultry as well as in crop- and grain farmers. Our results show a positive correlation with chronic bronchitis and exposure to cattle, animal excrement, and fodder handling. A significant increase in the overall prevalence of chronic bronchitis in farmers was also observed in our study.
In conclusion, these results point to a health recommendation for respiratory protection of farmers, especially during activities where they are exposed to agricultural organic dusts and microbes. The education of farmers and improvements in dust control in their working environment are crucial. In addition, because barn air exposure has been recognized to be a risk factor, enhancements in the hygiene and ventilation in these barns could help in reducing harmful exposures.
A high response rate increases the validity of population-based studies, because a low response rate might lead to selection bias. Although the response rate in our survey was low, we were able to acquire completed questionnaires from over 2500 farmers, the study population representing different farming sectors and all geographical areas in Finland. However, we focused on comparing the prevalence of symptoms and disorder between different occupational sectors instead of generating estimates to entire farming population. Possible bias might exist both in the selection and in the reporting of symptoms confounding the connection between a risk factor and the prevalence of a symptom/disease. It is possible that those with symptoms are more likely to respond to the questionnaire. Farmers can also influence their own working environment compared with, for example, industrial workers. Furthermore, the low response rate fails to explain the differences we observed in the prevalence of symptoms and disorders in several farming sectors.
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