Effects of exposure to dust in swine confinement buildings--a report.

D. Effects of exposure to dust inswine confinementbuildings - a working group report. Scand J Work Environ Health 1989;15:309-312. Pulmonary and other symptoms among workers in swine confinement buildings were evaluated by an international working group. In several studies in five different countries a total of about 2000 workers has been studied in clinical and epidemiologic investigations. Symptoms indicative of acute and chronic airway inflammation were widespread, as were systemic reactions of organic dust toxic syndrome. The base-line, and across workshift, pulmonary function changes were moderate. There was no evidence that antigen.antibody reactions are important in the pathogenesis. Longitudinal studies are recommended to establish the relationship between acute and chronic symptoms and end stage disease.

Reprint requests to: Professor R Rylander. Department of Environmental Hygiene, University of Goteborg, Box 33031. S-400 33 Goteborg, Sweden. treatment, a nd co mpensation . This approach has previou sly been used to sum ma rize information on the expo sure effects of co tt o n du st (2).
Organic du st exposure is also present in swine co nfinem ent buildings. The fir st studies on the health o f persons wo rking in sw ine confinement buildings were published in the United States (3) and Finland (4) , fo llowed by severa l reports from the United Sta tes, The Netherlands, Canada, and Sweden (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). A working gro u p was assem bled to summarize the sympto matology, clini cal findings, and pathogenesis of the expo sure. A di stinction wa s made between cha nges a ppearing a ft er acute exposure and those present a ft er prolon ged exposure . Dose-response relationships for d ifferent specific ag e nts in the environment were d iscussed . Effects o f toxic gases which also mi ght be present in thi s environment (eg, hydrogen sulfide and ammonia) were not discussed. This paper presents a summation of the working group's findin gs.
Wheezin g a nd che st tightness are al so common , in 12 to 35 % of the expos ed populations. In seve ra l of the studies, sym pto ms were more than twice as common as in the reference g ro u p (8,13,16,18). In add itio n sho rt ness of breath wa s pre sent in up to 20 % o f the workers (13,1 6-1 8). Longer exposure periods were related to th e feelin g of chest tightness.
Data from some studies suggest that younger workers with a short history in pig farming report only symptoms of irritation in the airways, whereas workers with a longer history report cough with phlegm (chronic bronchitis) and occupational asthma-like symptoms (11). This finding has been supported by the results of other studies (5,6,10,16).
The respiratory symptoms may occur with varying exposure patterns. Some recent data suggest that in many persons cough, phlegm, and chest tightness appear during the first day after time off work. This finding is similar to the symptoms of cotton workers, and the finding may be relevant to an understanding of the pathogenesis of the illness. However, among swine workers, the periods off work are very irregular, and a systematic evaluation of these "Monday" symptoms is difficult.

Systemic and other symptoms
Episodes of a febrile illness with influenza-like symptoms, including malaise, muscle aches, joint pain, and fatigue, are experienced by 5 to 20 !T/o of swine confinement workers (5,8,13,(16)(17)(18). These symptoms are consistent with what has been described as the organic dust toxic syndrome (1). This syndrome is often reported 2 to 6 h after an unusually heavy exposure to a variety of organic dusts.
Irritation of the eyes, nose, and throat and a dry cough are commonly reported (5,8). These symptoms suggest that this work environment causes a general inflammation of the mucous membrane. Another group of symptoms often reported includes stuffy nose, "popping" ears, continuous cold, headaches, and dizziness (8). These symptoms are also consistent with an inflammation in and swelling of the epithelium in the nasopharyngeal area.
One epidemiologic study suggests that the swine confinement environment might lower the resistance of the respiratory tract to infections (16). This study reported that 16 % of the Swedish swine farmers studied had a previous history of pneumonia confirmed by a physician as compared to 6 % of the reference group. In addition, frequent chest cold was reported by 53 % of the workers as compared with 20 % of the referents. This finding is consistent with 30 !T/o of the workers reporting that they have had to take time off from work as a result of respiratory illness, compared to 18 % of the referents.

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In support of this finding, one animal study has demonstrated that the swine environment can severely damage the respiratory epithelium (7).

Clinical and epidemiologic studies
Lung function -base-line changes Pulmonary function studies have so far been performed on a total population of approximately 1000 farmers and pig farm workers in eleven independent studies in five countries (6,8,10, II, [13][14][15][16][17][18]20). Several of these population studies reported small mean decreases in the base-line lung function when compared with reference values; these differences remained after standardization for smoking (13,15,16,18). Clinically significant lung function decrements have been found in 15-20 % of the working population (11,18). Most of these studies refer to measurements of forced vital capacity and the forced expiratory volume in I s. Flow-volume parameters were decreased in some studies (8,16).
Dose-response relationships between lung function changes and exposure have been suggested in three studies (6,10,16). There is information suggesting a relation between base-line lung function and several exposure variables, like duration of exposure during the day or the years of employment (10). Such relations have also been found for certain exposure agents, eg, dust, ammonia and endotoxin (3).

Lung function -across shift changes
Changes in lung function across a workshift or workday have been reported in several studies (6,15,16). In all these studies the average decrease was small and seldom exceeded 5 % of the base-line value (6,8). As compared with base-line values, 15-20 % of the population have clinically significant work-period decrements (16). There were indications of relationships between the workday change in lung function and exposure to endotoxin and ammonia. In one study (7), the work-period decrements were significantly related to endotoxin exposure.
No clear relations to total dust or respirable dust fractions have been reported.

Serology
Only a few studies have evaluated the relation of atopy to the development of symptoms and lung function changes (4,16,20,21). The number of workers studied has usually been small, and appropriate reference groups have sometimes been lacking.
In a Dutch study (21), 13 !T/o of 130 pig farmers had elevated levels of immunoglobulin (Ig) E antibodies against storage mites, detected by the radioallergosorbent test. However, 70 % of these farmers also had an elevated IgE level again st hou se du st mite (Derma tophygoides) allergens. No IgE antibodies were found again st swine ant igens; this findin g is consistent with the results of a Finnish study (4). Another study showed no difference in precip ita ting antibod ies to agents related to hypersensitivity and swine ant igens and molds isolated from the swine environment (16).
In an unpublished Dutch study (Brouwer et al, persona l communication) elevated levels of IgG4 a ntibodies were seen amo ng subgro ups o f swine co nfinement workers involved in intensive forms of pig far ming. Relat ionships were seen between respirator y compla ints during, or shor tly a fter work and th e IgG4 levels in serum aft er adjustment for age, smoking, an d end otoxin exposur e. Another study reported eleva ted levels of IgG antibodies again st swine antigens (4) in comparison with the levels of referenc e gro ups, but th ere were no corr elations with respiratory sympt oms. Matson et al (22) st udied the occurrence of IgG and IgE antibodies . Some farmers had elevated levels of a ntibodies to swine antigens, but in none of th e cases co uld the presence o f elevat ed levels of antibod ies be correlated with sympto ms.

Pathogenesis
Th e question concerni ng a causa tive agent(s) for the symptoms an d clinical findin gs pre sented in the preceding discussion has not been resolved. Several of the symptoms and pulmonary fun ction deficits ar e closely related to bacterial endotoxins, but associat ions also exist between du st levels, ammonia, and other agents. Severa l potential toxic agents a re pre sent in the swine con finement enviro nment (3), and it is at present impossible to exclud e a possible role for the se in addition to the ones presented in the pre ceding discussion.
In view of the imprecise do cum ent ation on causative agents, conclusio ns co ncerni ng th e pathogenesis behind the observed symptoms and clinical changes remain uncer tain. Several of th e effects describ ed can , however, be caused by acute or chronic inflammat ion of the airway s. Many agents in the swine con finement en vironment , such as endo to xins, ammonia , and hydr ogen sul fide , ma y indu ce inflamma tio n causing swelling and edema of the epith elium or indu ce contraction of bron chial smooth muscle. Both events cause nar rowing of th e airway lumen . Experience also indicates that this infla mmatio n may ca use an increased bron chial reactivity to other inha led agents, such as tob acco smo ke. The combined effects of organ ic du st a nd to bacco smoke may occur in a synerg istic manner and decrease defense mechanisms to inha led microorganisms. This may be th e reason for the increased frequency of upper respiratory infections observed in some studies. Inflamm ation may also develop in other co ntact sur faces, such as the epithelium in the nasal passages o r in the eye, and cause subjective irritation.
Th e ro le of traditional immunologic mechanisms, pa rticularl y the type-III reaction (antigen-antibody reaction s) remains ob scur e. In spite of ef for ts to cha racterize the imm unologic respon siveness of the host (ato py) and the determination of antibodies agai nst various ant igens in the swine confinement build ing air, no clearcut relationships have been demon strated. An increase in a specific subclass of antibodies may indicate the involvement of antibodyant igen reactions, but it may also simply reflect the expos ure. General increases in antibody levels are also found af ter a genera l stimulatio n of th e immune system thr ough inflamm atory and adjuvant agent s, such as endotoxins.

Comments
Inform at ion on repo rted symptoms is important for attending physicians, occupational hygienists, engineers, managers, and the employees themselves. They must recognize that a series of local and general symptom s may be caused by exposure to the swine confinement environment. These sympto ms are common in exposed gro ups, and th e ind ividual may suffer considera ble discomfort and be forced to leave work. Although the symptomatology and clinical finding s reported do not adhere to the criteria of trad ition al occup ation al lung diseases (ast hma , hypersensiti vity pneum onitis, pneum oconio sis), they should, nevertheless, be recognized as posing a health ha zard, and action should be taken to decrease the risk of the work ers.
The information on do se-respon se relation ships and different agents for th e development o f symptoms and clinical findin gs is as yet limit ed. Th e most compl ete informat ion availabl e refers to endotoxin , for which dose-respon se relationships ha ve been demonstrated for an acute decrease in th e forced exp iratory volume in I s ove r the wo rkshift, and for cough, phlegm , wheezing, chest tightness, and fever as well. The importan ce of other agent s, such as ammon ia and oth er irritating gases, other microbial products (such as glucan s and mycoto xins), and the particle s themselves , needs to be investigated further.
For the purposes o f long-term prevention , the relation between acute effects over the wo rkshift and th e risk for lon g-term effects needs to be evalua ted. Th e onl y means with which to obtain such information is to perform longitudin al studies, in which persons starting work in swine con finement buildings are screened for airway reactivity, atopy, the presence of symptoms aft er an exposure period, and pulmonary function . The se workers need to be followed on a regular basis . For th ose who leave t heir work in swine confinement buildings, the reason s, particularly if related to adverse pulm on ar y reaction , sho uld be do cumented. Furthermor e, dose-respon se relatio nships between irr itating gases, other microbial products such as glucans , and the particles themselves need to be investigated further.