Recent years have seen the successive evolution of swine production in Canada through mainly three stages, from small, largely outdoor production with minimal respiratory exposures to the farmer, to larger, intensive indoor operations on individual farms managed by the farmer owner/operator experiencing intermittent exposures, to the current, large commercial facilities operated by workers employed full time experiencing > 8 h/d of respiratory exposures. Almost all of our current understanding of the respiratory health effects of ambient exposures in intensive swine production facilities has come from studies on individual male farmers during the 1980s and 1990s who experienced intermittent “2 to 3 h/d” exposures that have demonstrated increases in respiratory symptoms, reductions in expiratory flow rates, and increases in bronchial responsiveness. Across-shift studies have demonstrated acute reductions in pulmonary function test variables, increases in bronchial responsiveness, and increases in inflammatory mediators. Longitudinal studies have demonstrated increases in bronchial responsiveness, excess decline in pulmonary function test variables, with acute across-shift changes predicting longitudinal decline in measures of lung function.
The relationship of respiratory effects to indoor occupational air contaminants including dust, endotoxin, ammonia, and hydrogen sulfide have been described. The study that we herein describe is to our knowledge the first report on the respiratory health effects incurred by workers employed full time in the recently developed, indoor, large-scale, corporate intensive swine production facilities that also includes robust numbers of both women and men.
The study was conducted in rural Saskatchewan, Canada. Swine workers were recruited with the collaboration of SaskPork, the pork producers’ association in Saskatchewan, and large swine production companies in Saskatchewan. A description of the study was posted in the SaskPork periodic newsletter, and visits encouraging participation were made to executives of the swine production companies. The large swine production companies cooperated by encouraging all workers to attend the evaluation clinics that were held in nearby towns and villages. The companies cooperated by scheduling the workers into prearranged time slots. All workers were given the opportunity to participate. To participate in the study, swine workers had to be > 17 years old and had to work in the confinement building for at least 4 d/wk with a total work duration of > 20 h/wk. The majority of people in Canada prefer to make order of drugs via My Canadian Pharmacy www.my-medstore-canada.net.
In this study, 374 workers were chosen from 38 large swine operations. The number of workers chosen from each swine operation varied from 3 to 37, resulting in varying response rates for each operation. Nonfarming control subjects were chosen from all nonfarming rural dwellers that were residing within an approximate 100-kilometer radius of a swine production site. A form was sent to all persons in the taxation list provided by the rural towns located in proximity of the swine production sites. Nonfarming rural dwellers who were involved in mining, grain handling, metal, and auto-body work were not considered for selection of control subjects.
All interviews and testing were conducted in hospitals and community centers that were located near the swine production sites and the residence of the nonfarming control subjects. A person-to-person interview was conducted by a trained technician who completed the questionnaire by recording participants’ responses to the questions in the questionnaire. The study was approved by the Biomedical Research Ethics Board of the University of Saskatchewan. Prior to the interview, informed written consent was obtained from all subjects.
The participation rate from the large swine operations was approximately 70%. Of the 374 swine workers who participated in the study, 240 were men and 134 were women. Of the 411 nonfarming rural dwellers who participated in the study, 184 were men and 227 were women. The age of the swine workers and nonfarming control subjects ranged from 17 to 65 years.
Medical and Occupational History
A respiratory health and occupational history questionnaire was administered by a trained technician to all participants. The questionnaire used in previous studies was modified to include questions related to current practice in the swine industry. The presence of usual cough was obtained from an affirmative response to the question, “Do you usually have a cough (count a cough with first smoke or first going outside, do not count clearing the throat)?” The presence of chronic cough was obtained from an affirmative response to the second question in a series of two consecutive questions, “Do you usually cough as much as four to six times a day > 4 days out of the week?” and “Do you usually cough like this on most days for > 3 consecutive months during the year?” The presence of usual phlegm was obtained from an affirmative response to the question, “Do you usually bring up phlegm from your chest (count phlegm with first smoke or first going outside)?” The presence of chronic phlegm was obtained from an affirmative response to the question that followed the question on usual phlegm, “Do you usually bring up phlegm like this as much as twice daily > 4 days out of the week?” The presence of wheeze was obtained from an affirmative response to the question, “Does your chest ever sound wheezy or whistling occasionally apart from colds?” The presence of shortness breath was obtained from an affirmative response to the question, “Are you troubled by shortness of breath when hurrying on the level or walking up a slight hill?” The presence of asthma was obtained from an affirmative response to the question, “Has a doctor ever told you that you have asthma?”
The years of employment in any swine operation were obtained from the response to the question, “How long have you worked in a swine confinement unit?” Days per week and hours per day spent in the current workplace were obtained from the question, “How many days a week and hours a day do you spend in the barn?” The work-related activities and time spent in these activities were obtained in different swine production stages: farrowing, nursery, grower/finisher, breeding/gestation, and other activities. Farrowing is the stage during which the sows give birth and piglets are kept with the sow until they are weaned (up to 3 weeks). After weaning, the piglets are kept in nursery until they reach 8 to 12 weeks of age and are moved to grower/finisher units until they reach 100 to 120 kg. They are then shipped to the market or used for reproduction purposes. The pigs are usually approximately 25 weeks of age when they leave for the market. In the breeding/gestation section, sows are bred and kept during the gestation period until they are moved to farrowing rooms. The “other” category included working in office areas, maintenance that cannot be linked consistently to a single production area, indoor washing of the facility, working in feed mill and/or laboratory, and handling boars for semen production. A worker may engage in more than one of these activities on a single working day. The categories in production stages are not mutually exclusive, and the proportion of workers in these categories will not add up to 100%. For the same reason, mean hours spent in these production stages cannot be added to obtain the total hours spent in a day in the swine operation.
Lung Function Measurements
Pulmonary function testing was performed by trained technicians using a volume displacement spirometer (model 1022; SensorMedics; Yorba Linda, CA) and testing techniques that followed American Thoracic Society recommendations. The following parameters were recorded: FEV1, FVC, FEV1/FVC ratio, and forced expiratory flow between 25% and 75% of FVC (FEF25-75%). Percentage of predicted values for FEV1, FVC, FEVj/FVC ratio, and FEF25-75% were obtained from equations developed by Crapo et al.
Smoking habits were defined as current smokers, persons currently smoking cigarettes; ex-smokers, persons who have smoked > 400 cigarettes (or equivalent amount of tobacco) in his/her lifetime but not currently smoking; and nonsmokers, persons who have not smoked > 400 cigarettes (or equivalent amount of tobacco) in his/her lifetime. Quit smoking cold turkey with remedies of My Canadian Pharmacy.
Continuous variables were described with means and SD. Frequencies and percentages were used to describe the categorical variables. Differences in continuous variables were examined by Mann-Whitney U tests to allow for skewness in the distributions and violation of equal variance assumption in the standard two independent-sample t tests. x2 test was used to test the differences in smoking between swine workers and nonfarming control subjects. Multivariate logistic regression analyses were used to determine the association between respiratory symptoms and working in swine operations after controlling for age and smoking. We also conducted independent dose-response analysis between years of employment and symptoms in male and female workers after controlling for smoking using logistic regression analysis. A three- of variance was conducted to determine jointly the significant differences in percentage of predicted lung function between mask users and nonusers and the swine operations after controlling for smoking.