Occupational Health Risks for Swine Producers:
Inferences for Public Health Risks of People
Living in the Vicinity of Swine Production Units

Kelley J. Donham
The University of Iowa

It was in 1977 that the first paper was published on the occupational health risks of working in intensive swine housing facilities (Donham, et al. 1977). Since that time, numerous additional studies in the U.S., Canada, Sweden, Finland, the Netherlands, Germany, Denmark, and Great Britain have all had similar results providing convincing documentation of the occupational health risks of swine producers (Bongers, et al. 1987; Cormier, et al. 1991; Crook, et al. 1991; Donham 1993; Haglind, Rylander 1987). The studies have consisted of case reports, and epidemiological, environmental, dose-response, and clinical studies. Although these studies have focused on risks to the respiratory system, there are other risks such as hearing loss, injuries, accidental needle sticks, and zoonotic infections (Thorne, et al. 1996).

The first studies (in the late 70's and early 80's) were primarily surveys using standardized medical questionnaires (Donham, et al. 1977; Dosman, et al. 1988; Iverson 1988). These studies documented respiratory symptoms in swine workers that were in excess relative to respiratory conditions in control populations. These studies resulted in identifying acute symptoms of bronchitis and occupational asthma which occurred in 40%-60% of exposed workers. Subsequently, additional studies were done with standardized medical questionnaires that identified chronic conditions (conditions which existed for three or more years), particularly chronic bronchitis, occupational asthma, and sinusitis (Donham 1990; Dosman 1996; Holness, et al. 1987; Schwartz, et al. 1995).

These symptom surveys have been backed up by objective pulmonary function studies. The data from these studies indicated that workers' lung functions decrease during their working periods relative to controls. These pulmonary function decreases are primarily in forced expiratory volumes which suggest an obstructive condition being caused by narrowing of the airways. Additional studies have shown that changes in pulmonary function over a workshift are predictors of impending chronic loss in pulmonary function. Baseline pulmonary function data for FEV₁ and FVC have usually been normal. However, most studies have shown decrements in flow rates which are suggestive of impending obstructive conditions of the large airways (Schwartz, et al. 1990). Clinical studies utilizing bronchial examination and lavage have documented that a chronic airways inflammatory process is present in symptomatic workers (Schwartz, et al. 1995). Inflamed mucosal surfaces are obvious, and cells examined (primarily mononuclear and lymphocytic cells) from the bronchioles and lungs are indicative of a chronic inflammatory process. A systemic inflammatory process is also recognized by elevated white counts in workers over a working period (Donham 1990).

Several studies have been conducted to examine the allergic basis of conditions in swine producers. Most all of these studies have been negative, suggesting that there is a direct inflammatory or toxic process resultant from the inhaled air contaminants (Rylander 1994).

A recent review of the literature regarding occupational health concerns of swine producers summarized findings from 16 studies (Thorne, et al. 1996). The findings indicated that there are four major conditions that commonly occur in swine producers. These include: chronic bronchitis; nonallergic occupational asthma; episodes of organic dust toxic syndrome; and mucus membrane irritation (including chronic sinusitis). Additionally, the authors describe a fifth condition manifested by chronic fatigue, mild dyspnea, and syncope, which one researcher has hypothesized is a manifestation of a chronic organic dust toxic syndrome. This review reported that one or more of these conditions occur in 20%-35% of exposed individuals.

Furthermore, more than one condition may occur in a given worker.

The long-term sequelae and long-term outcomes of these respiratory conditions have been studied very little to date. However, one seven-year follow-up study in Canada resulted in a finding that 10% of a cohort of swine producers had to quit swine production because of health conditions related to the work environment (Holness, Nethercott 1995). A second Canadian study found a progressive decline in pulmonary function of a cohort of swine producers over a five-year study (Thorne, et al. 1996). Chronic symptoms have been found to occur primarily in workers who have been exposed two or more hours per day for a six year period or longer (Donham, et al. 1989).

Additional studies have shown that workers who smoke have an increased risk of developing symptoms, an increased severity of symptoms, and exacerbated pulmonary function decrements. Other risk factors include concurrent respiratory or cardiovascular conditions such as asthma or coronary heart disease.

Numerous environmental studies have shown that the air quality inside buildings is contaminated with organic dusts that contain extremely high levels of microbes, endotoxin, b 1,3 glucan and other potential toxicants (Heederik, et al. 1991). Furthermore, irritating or toxic gases are present in the same atmosphere, including ammonia; periodic levels of hydrogen sulfide and numerous other gases with a lesser known potential health sequelae. Several studies have documented a dose-response relationship between these environmental exposures, time of exposure, and health outcomes (Donham, et al. 1982). More recently, dose-response studies have resulted in recommending exposure limits of these gases and dusts to help ensure worker health is protected (Donham, et al. 1995). Table 1 is a listing of these exposure limit recommendations.

There have been only two published studies evaluating the air quality in the outdoor air surrounding swine facilities. The most recent study was conducted in Iowa (Reynolds, et al. 1997). This study examined the air environment surrounding facilities, and documented the presence of low levels of ammonia, dust and endotoxin. However, the levels found were very low relative to the levels found inside production facilities. For example, levels of ammonia found in outdoor environments were in the range of 1 ppm relative to an average indoor environment of 5-10 ppm. Dust and endotoxin levels found were near the limits of detection of the methods utilized. These levels were for example, less than .5 mg/m³ and endotoxins in the range of < 10 (endotoxin units/m³ of air). Concentration of these contaminants known to be associated with symptoms inside confinement facilities are on an order of magnitude higher than concentration found in the outdoor air. However, there was a direct association between the size of the facility (number of pigs) and the concentration of air contaminants found in the surrounding outdoor environment.

There have been two studies to date looking at symptomology of people living in the vicinity of swine production facilities. A standardized medical survey of residents living in the vicinity of a 2,500-sow unit resulted in a recording of respiratory symptoms significantly higher than those recorded in neighbors of farms where no livestock were raised (Thu, et al. 1997). The symptoms recorded were almost identical to those reported by swine confinement workers in terms of the bronchitic and occupational asthma symptoms, and with a similar frequency and constellation of symptoms appearing. This same study revealed no differences from controls in terms of psychosocial or behavioral symptomology. However, a previous study in North Carolina did indicate behavioral changes in individuals living downwind from facilities manifested by various mood alterations.

The cumulative research on occupational health symptoms and exposures is epidemiologically strong. The studies by different researchers in different countries all reach fairly consistent conclusions. However, it is difficult to understand the implications for health of individuals living in the vicinity of these structures. There has been one study to date that documents the existence of symptoms. It is notable that these symptoms are quite similar to those symptoms found in workers. The patterns and the frequency with which they are reported are similar. However, there was no individual environmental data taken in this particular study so it is not known what these people were being exposed to. Other environmental studies without symptoms assessed in workers, have shown the presence of the same intoxicants in the outdoor environment that are in the indoor environment. These toxicants are significantly lower than concentrations associated with symptoms in workers. Therefore, this data is difficult to interpret. One could suggest that although workers are exposed to higher levels, they are only exposed to these levels for part of the day whereas, residents may be exposed for 24-hour periods at a time.

Relationships between the psychosocial condition of the person and the physical symptoms and exposures that occur. As there has only been two studies to date of health hazards of area residents, one may look at other environmental exposures for insight. Sick building syndrome (SBS) may have some similarities (Martin, Yutzy 1994).

One suspected cause of SBS is mass psychogenic or sociologic illness. Psychological symptoms are usually accompanied by physical complaints (Boxer 1990). Often environmental toxins are not apparent. Perception of risk, feelings of no control of the situation, and poor communication are all associated with the syndrome (Star, Gibson 1985). Additionally in these situations, there may be no known exposure level that exhibits symptoms, but it seems that levels that just remind the person of existence of a situation will result in symptomology.

Similar situations have occurred in larger outdoor environmental situations such as Love Canal in New York, Times Beach in Missouri, Three Mile Island in Pennsylvania, as well as the Agent Orange Vietnam War situation and the more current Gulf War situation. All situations where symptoms are well documented but extremely difficult (if at all) to find concentrations of a toxicant that might explain the situation. In all these situations there were certainly levels of stress and psychosocial concerns involved. In fact, there has been a condition coined environmental stress syndrome, which has many similarities to the situations seen in some neighborhoods surrounded by recently built large swine facilities.

In summary, we know exposures of gases and dusts inside swine buildings result in high levels of respiratory disease in workers. Regarding people living in the neighborhood of swine production facilities, they may experience symptoms similar to workers. However, levels of toxicants measured in the outdoor air are significantly less than what is associated with occupational illnesses. These concentrations are not apparently high enough to cause disease by themselves. One must believe however, that the neighbors' symptoms are real. I hypothesize that there is some very complex interaction between the psyche and physical symptoms seen. People feeling stressed, and out of control are vulnerable to even the suggestion of toxicants in their environment. Similar situations have been found in workers in "sick" buildings, and residents in the neighborhood of highly publicized environmental events such as Times Beach, Missouri, Three Mile Island, Pennsylvania, and Love Canal, New York. Further research is required to fully understand this phenomenon, coined by some as environmental stress syndrome.

To Top