AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 35:310–316 (1999)
Back Pain and Agricultural Work Among Farmers: An Analysis of the Colorado Farm Family Health and Hazard Surveillance Survey Huiyun Xiang, MD, MPH, Lorann Stallones, MPH, PhD,* and Thomas J. Keefe, PhD
Background Back pain is the most prevalent occupational health problem experienced by much of the world’s workforce. However, agricultural work-related back pain occurring among US farmers working on small operations or family farms is usually not included in surveillance. With data collected by Colorado Farm Family Health and Hazard Surveillance Survey, this study reports characteristics of and risk factors for back pain among adult farmers living in eight Colorado counties. Methods A stratified probability sample of 500 farms was selected in proportion to the number of farms in study areas. During the 4-year period from 1993 through 1996, 458 farms were enrolled in the study and 759 farmers were interviewed using a questionnaire. Information on self-reported back pain and potential risk factors among 742 white farmers was evaluated and reported here. Results A total of 194 farmers (26.2%) reported to have had at least one episode of back pain lasting for 1 week or more. Males had a slightly higher prevalence of back pain than females (28.6% vs. 22.5%) and the lower back was the predominantly affected part of body among both males and females. In 45.4% of males and 43.9% of females back pain was brought on by repeated activities. Males’ activities at work were more likely to cause back pain while females’activities at home were more likely to cause back pain. Three factors were found to be significantly associated with back pain: being depressed (odds ratio (OR) ⫽ 3.68, 95% confidence interval (CI) ⫽ 2.23–6.09), farming/ranching as main activities (OR ⫽ 1.66, CI ⫽ 1.17–2.36), and worked in agriculture for 10 to 29 years (OR ⫽ 1.62, CI ⫽ 1.14–2.30). Conclusions Our analyses indicate that back pain is an occupational health problem among farmers on small operations or family farms and that back pain affected males and females differently. The finding of significant positive associations between depression, farming activities, and back pain warrants further attention.Am. J. Ind. Med. 35:310–336, 1999. r 1999 Wiley-Liss, Inc. KEY WORDS: back pain; agricultural work; farmers; risk factors; depression
INTRODUCTION Back pain is the most prevalent occupational health problem experienced by much of the world’s workforce
Colorado Injury Control Research Center, Department of Environmental Health, Colorado State University, Fort Collins, Colorado Contract grant sponsor: National Institute for Occupational Safety and Health Cooperative Agreement; Contract grant number: U04/CCU 806060. *Correspondence to: Dr. L. Stallones, Department of Environmental Health, Colorado State University, Fort Collins, CO 80523–1676. E-mail:
[email protected]. Accepted 6 November 1998.
r 1999 Wiley-Liss, Inc.
[Deyo et al., 1991]. National estimates of back pain among US workers and occupations at high risk of reporting back pain have been reported based on the data from the 1988 National Health Interview Survey, Occupational Health Supplement (NHIS/OHS) [Guo et al., 1995; Park et al., 1997]. In the US, 10–17% of the adult population over age 25 experience an episode of back pain each year. Lifetime prevalence has been estimated at nearly 70% for industrialized countries. Studies have evaluated back pain and the associated risk factors among nurses, miners, truck drivers, and material handlers [Harber et al., 1985; Kaplan et al., 1988; Garg, 1992; Bernard, 1997]. However, data about injuries (including work-related back pain) occurring among
Back Pain Among Colorado Farmers
US farmers working on small operations or family farms are usually not included in available surveillance [Bobick et al., 1995]. The etiology of back pain is multifactorial [Anderson, 1981; Bernard, 1997; Burdorf et al., 1997; Dempsey et al., 1997]. Risk factors associated with back pain can be categorized in two groups: 1) occupational factors, and 2) characteristics of the workers. Studies examining occupational factors have reported that heavy manual work, static working postures, jobs involving vibration, repetitive tasks, and vehicle driving are risk factors for long-term back pain [Heliovaara, 1993; Bernard, 1997]. The patterns of back pain have been fairly consistently reported across these studies. With respect to personal risk factors for back pain, age, gender, education level, smoking, and psychosocial factors have been studied [Bernard, 1997]. However, the inclusion of personal variables in epidemiologic studies of back pain has been inconsistent, and the results obtained from those epidemiological studies which evaluated personal risk factors for back pain were inconclusive. While the etiology mechanisms are poorly understood, there is increasing evidence that psychosocial factors related to the job and work environment play a role in the development of work-related musculoskeletal disorders (MSDs) of the upper extremity and back [Bernard, 1997]. A number of studies have found associations even after adjusting for physical demands; therefore, the effects of psychosocial factors on MSDs were suggested to be, in part or entirely, independent of physical factors, which may represent generalized risk factors for work-related MSDs [Bernard, 1997; Dempsey et al., 1997]. To better understand the prevalence and characteristics of back pain in a farming population and to study potential risk factors in light of multifactorial causes, this article reports results of self-reported back pain among adult farmers who resided in eight Colorado counties using data collected by Colorado Farm Family Health and Hazard Surveillance (CFFHHS) during a 4-year period from 1993 through 1996. The relative risk of back pain was estimated by agricultural work activities and personal factors: gender, age, education level, cigarette smoking, and psychological stress.
MATERIALS AND METHODS Study Design and Study Population The study design and population have been previously described in detail [Champney et al., 1996]. In summary, a stratified probability sample of 500 farms in eight northeastern Colorado counties (Sedgewick, Phillips, Yuma, Logan, Washington, Morgan, Weld, and Larimer) was selected by the CFFHHS in proportion to the number of farms in study areas reported in the National Agricultural Statistical Report-
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ing Districts for Crop and Livestock Reporting. Farms were chosen from randomly selected township/range units within each of the eight counties on the basis of the proportion of agricultural land use, the average acreage of the farms, and the probability that the principal operator was a resident on the selected farm. Each residence within the township/range unit was identified using rural directory maps and county property tax assessors’ records. The determination of whether or not the dwelling was a farm was based on the definition used by the Census of Agriculture as a place that sells $1,000 or more in agricultural products in an average year. If the dwelling was eligible for the study, the principal farmers residing on the farm were asked to participate in the survey. The 4-year survey was initiated in January 1993 and data collection was completed in December 1996. A total of 458 farms agreed to participate in the study, representing 759 individual farmers. Seventeen participants were minorities and were excluded from the analysis in this report due to small numbers and the fact that studies have indicated that race is a risk factor for back pain [Bernard, 1997; Dempsey et al., 1997]. Thus, the study population consisted of 742 white farmers.
Study Variables All of the enrolled farmers were interviewed using the CFFHHS questionnaire, which was patterned after the one used in the 1988 NHIS/OHS. The final questionnaire was pilot-tested among a small group of Colorado farmers before the formal survey. Questions regarding musculoskeletal conditions obtained detailed information on back pain, including its occurrence, part of the back hurt, whether or not the back pain was brought on by repeated activities (such as lifting, pushing, pulling, bending, twisting, or reaching), and the consequences of the back pain. The ‘‘back pain’’ cases were defined as those farmers who answered ‘‘Yes’’ to the question ‘‘At any time during the past 12 months, that is since (12 month date) a year ago, did you have back pain every day for a week or more?’’ Noncases were defined as those who answered ‘‘No’’ to the question. Other parts of the questionnaire addressed general farm characteristics, use of farm chemicals, demographic information about farmers and their family members, general health, detailed work history, cigarette smoking history, and behavioral/psychosocial factors. In this report, cigarette smoking history was grouped according to regular cigarette smoking years, school years were divided into three categories (12 or less years, 13–15 years, and 16 or more years), and psychosocial symptoms were grouped together to indicate depression status. Depressive symptoms were determined using the Center for Epidemiologic Studies Depression (CESD) scale, which contains a series of 20 psychosocial
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questions and has been used in numerous studies [Radloff, 1997; Goldberg et al., 1985; Stallones et al., 1995]. The possible score from this scale ranges from 0 to 60. The CESD scale has been shown to be a valid screening tool for detecting depressive symptoms in general populations as well as in psychiatric populations. A score of 16 or higher has been used by other investigators [Goldberg et al., 1985; Stallones et al., 1995] to indicate depression status and, thus, was used in this report to indicate psychological depression among those farmers. Agricultural work exposures were assessed by occupation, years employed in agriculture, and primary farming activities on farm. Occupation was categorized as: farming/ ranching, home-making, and other employment. Years employed in agriculture was divided into three groups as follows: 1–9, 10–29, and 30 or more. Primary farming activities on farms were grouped as: field and crop production, livestock, and all others (forest, horticulture, vegetable, melon, nut, and fruit). All of the data regarding characteristics of farms were obtained by interviewing owners of the farms.
Statistical Methods SAS version 6.12 was used for data analysis in the study [SAS, 1990]. Both the prevalence of back pain and the characteristics of back pain (e.g., part of the back injured, whether or not the back pain was brought on by repeated activities, such as lifting, pushing, pulling, bending, twisting, or reaching, and the consequences of the back pain), were reported separately for males and females. Percentage of reported back pain, univariate odds ratios (OR) and the associated 95% confidence intervals (CI) were computed using the SAS FREQ procedure for each risk factor. Multivariate logistic regression models were used to calculate the adjusted ORs, along with 95% CIs, by including all risk factors of interest in the models. In multivariate logistic regression analysis, a hierarchical approach was used. The potential personal risk variables for back pain (age, gender, education, and cigarette smoking) were entered into the model first. Next, depression status was added. In the third step, agricultural work factors (occupation, years in agriculture, and primary farm activities on farms) were entered. Depression status was entered in the second step for two reasons: there is increasing evidence that psychosocial factors play an important role in the development of work-related musculoskeletal disorders of the upper extremity and back; and the effects of psychosocial factors on MSDs were suggested to be, in part or entirely, independent of physical factors [Bigos et al., 1991; Bernard et al., 1994; Kidd et al., 1996; Bernard, 1997]. Finally, the stepwise selection modeling technique was used to select statistically significant risk factors for back pain. By comparing changes in both ORs and corresponding 95% CIs obtained from
different models, this data analysis strategy has been shown to be helpful in interpretation of complex hierarchical interrelationships between study variables and outcomes [Victora et al., 1997].
RESULTS Of those 458 farms investigated, 4.9% were small farms between 1 and 49 acres, 27.8% were between 50 and 499 acres, 35.0% were between 500 and 1,999 acres, and 32.3% were over 2,000 acres. The leading cash products on those farms were field crops and cash grains (63.5%) and livestock (30.4%). In terms of agricultural products sales, 46.6% of those farms had more than $100,000 sales value of all products, 26.1% had sales value of all products between $40,000 and $99,000, and 27.4% had sales value of all products below $39,000. Most (86.4%) of the farms employed less than five regular farmers. All of the interviewed males (448) and a majority of the interviewed females (244/294) reported being involved in farming activities in the year preceding the survey. Among the 742 respondents (448 males and 294 females), a total of 194 farmers (26.2%) had experienced at least one episode of back pain lasting for a week or more during the 12 months preceding the survey. Table I presents a gender-specific description of back pain among the respondents. Males had a slightly higher prevalence of back pain than females. For both sexes, the lower back was the predominantly affected part of the back. In 45.4% of the male cases and 43.9% of the female cases, back pain was brought on by repeated activities such as lifting, pushing, pulling, bending, twisting, or reaching. Only 13.0% of the male cases and 7.6% of the female cases were caused by single incidents, such as slipping, falling, twisting, or being in a motor vehicle accident. When back pain occurred as a result of repeated activities, a statistically significant difference was observed between males and females in regard to when and where the back pain was likely to be caused or experienced. Males’ activities at work were more likely to cause back pain. For females, however, their activities at home were more likely to cause back pain. When back pain was caused by a single accident or injury, no statistically significant difference was observed between males and females in regard to when and where the back pain was likely to be experienced. Those females who reported being involved in farming activities had approximately the same prevalence of back pain (22.4%) as those females who reported not being involved in farming activities (20.8%). Thirty-seven percent of the males and 30.3% of the females with back pain episodes had to make major changes (not defined) in work activities because of back pain, while about 10% and 8%, respectively, had to change or stop their work permanently due to back pain.
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TABLE I. Number and Percentage of Back Pain in the Preceding 12 Months by Selected Characteristics, Colorado Farmers (n ⫽ 742) in Eight Counties, 1993–1996 Male Characteristic Back pain Yes No Part of back injured Upper Middle Lower Unknown Cause of back pain Repeated activities (R) only
Number
Female
Percent
Number
Percent
P-value
128
28.6
66
22.5
320
71.4
228
77.5
16
12.5
9
13.6
11 97 4
8.6 75.8 3.1
9 43 5
13.6 65.2 7.6
0.390 0.389
0.054
59
45.4
29
43.9
Single accident or injury (A) only Both (R) and (A) Other Unknown Location when back pain brought on by repeated activities At work At home, recreation site, etc. Location when back pain resulted from a single accident or injury
17 27 20 5
13.0 20.8 15.4 3.9
5 13 18 1
7.6 19.7 27.3 1.5
54 5
91.5 8.5
11 18
37.9 62.1
0.001
At work or at business Not at work Major changes in work activities because of back pain Yes Former job stopped or changed because of back pain Yes
13 4
76.5 23.5
2 3
40.0 60.0
0.133
49
37.7
20
30.3
0.306
13
10.0
5
7.6
0.579
Percentage of back pain, crude ORs, and associated 95% CIs are presented in Table II. Results of the hierarchical sequential logistic regressions are summarized in Table III. In the univariate analysis, those people with back pain episodes were significantly more likely to have depression (OR ⫽ 3.26, 95% CI ⫽ 2.04, 5.22) and to have been employed in agriculture for 10–29 years (OR ⫽ 1.83, 95% CI ⫽ 1.01, 3.31). In the sequential multivariate analysis, entering occupational variables into the models altered the statistical significance of the relationships between back pain and personal variables (age and gender). When all of the variables were included in the logistic model, only depression was significant. In the stepwise selection model, depression, occupation as farming and/or ranching, and years in agriculture were found to be statistically significant variables. Throughout the analyses, the strong positive association between depression and back pain did not change. Although people involved in activities of ‘‘other’’ farming (i.e., forest, vegetable, melon, nut, fruit, and horticulture) had a higher risk of back pain, the association was not statistically significant (OR ⫽ 1.31, 95% CI ⫽ 0.31–4.71).
DISCUSSION In the current cross-sectional study, many of the findings about back pain and the associated risk factors reported in other industrial settings were observed in this farming population. However, the 12-month prevalence of 26.2% was higher than that found in other population-based studies in the US. Park et al. [1997], in their analysis of 29,322 working adults interviewed in the 1988 National Health Interview Survey, found that annual back pain prevalence ranged between 14–24%, with an annual prevalence of 17.8% found among workers employed in farming, forestry, and fishing. In this study, there was a strong relationship between back pain episodes and repeated activities, such as lifting, pushing, pulling, bending, twisting, or reaching, with the majority of back pain episodes caused by repeated activities. This is consistent with the conclusion drawn by Bernard [1997] in a recent review of over 40 epidemiologic studies regarding back pain and associated risk factors among all industrial or nonindustrial populations. A study conducted
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TABLE II. Percentage of Reported Back Pain, ORs and 95% CI for Study Characteristics Associated With Increased Risk of Back Pain Among Colorado Farmers, 1993–1996 Number in Percent of Characteristics Gender Male
study sample
reported back pain
Unadjusted OR (95% CI)
448
28.60
1.38 (0.98–1.95)
Female Age in years 20–29
294
22.45
Referent
22
40.91
2.24 (0.90–5.57)
30–39 40–49
144 214
29.86 26.64
1.38 (0.85–2.23) 1.18 (0.75–1.83)
50–59 60⫹ Years of school
157 199
24.20 23.62
1.03 (0.63–1.69) Referent
12 or less 13–15 16 or more Years of cigarette smoking Nonsmoker 1–15 16–25 25⫹
323 231
23.53 29.00
0.83 (0.55–1.25) 1.10 (0.72–1.69) Referent
463 78 77 121
25.70 26.92 32.47 23.97
Referent 1.07 (0.62–1.83) 1.39 (0.83–2.34) 0.91 (0.57–1.45)
74 668
50.00 23.47
3.26 (2.04–5.22) Referent
429 161
29.37 20.50
1.36 (0.89–2.10) 0.85 (0.49–1.45)
150
23.33
Referent
Depression Yes No Occupation Farming or ranching Home making Other (student and nonfarming related) Years employed in agriculture 1–9 10–29 30⫹ Primary cash crop Field and crop production Animals and livestock (beef cattle, dairy, feedlot, sheep, hogs, goats) Other (forest, vegetable, melon, nut, fruit, horticulture)
85
20.00
Referent
239 415
31.38 22.89
1.83 (1.01–3.31) 1.18 (0.67–2.12)
498
25.90
Referent
232
26.18
0.98 (0.69–1.40)
12
33.33
1.43 (0.43–4.81)
by Bishu et al. [1989] surveyed 44 farm workers to determine personal and task characteristics that contributed to back pain. These researchers found that, overall, the greatest risk for back pain was manual lifting tasks in the field at ground level. Studies of back injuries in farming men and women are rare, and reports with identical work tasks are virtually
nonexistent [Kraus et al., 1997]. Our finding that, unadjusted for occupational factors, the risk of back pain was higher in men than in women is consistent with that reported by Kraus et al. [1997], and by Abenhaim et al. [1987]. But it is contrary to several community-based surveys, which have consistently shown women at higher risk [Dempsey et al., 1997]. In fact, the results of this study indicated that activities of males at work were more likely to cause the back pain than activities at home. For females, however, their activities at home were more likely to produce back pain episodes. The overall difference in back pain episodes experienced between genders was found to decrease or disappear after adjustment for agricultural occupational factors. In the current analyses, when agricultural occupational factors were included in the logistic models, gender became a nonsignificant risk factor for back pain (OR changed from statistically significant 1.58 to nonsignificant 1.15). While the etiologic mechanisms are poorly understood, there is increasing evidence that psychosocial factors related to the job and work environment play a role in the development of work-related MSDs of the upper extremity and back [Bernard, 1997]. In a recent review, researchers found that psychosocial factors are seemingly unrelated to physical demands and the associations between the psychosocial factors and back pain episodes remained after adjusting for physical demands [Bernard, 1997]. It has been suggested that psychosocial factors may represent generalized risk factors for work-related MSDs. Most studies related to back pain among agricultural populations [Thu et al., 1990; Parton et al., 1990; Bobick et al., 1995; Palmer, 1996; Lower et al., 1996] did not evaluate psychosocial factors. One study [Manninen et al., 1995] did assess the association between mental stress and back pain in a study of middle-aged farmers, but reported no association between mental stress and back pain. In our study, a strong association between depression and back pain episodes was found; further, the relationship remained after adjusting for all personal risk factors and occupational factors. The results seem supportive of the theory that depression represents a generalized risk factor for back pain. However, because this is a cross-sectional study, it is impossible to infer a causal relationship between depression and back pain episodes. The depression symptoms might result from the back injuries and the associated suffering, or the depression might prompt those farmers who were suffering from depression to be more likely to experience and report back pain. Unfortunately, on the basis solely of the current study, it is impossible to determine which came first. Gaining a thorough understanding of the relationship between back pain and depression proved to be extremely difficult [Dempsey et al., 1997]. Unlike mechanical or workplace parameters that are readily definable and can be easily measured, psychosocial factors rely on subjective measurement scales. How-
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TABLE III. ORs and 95% CI for Study Characteristics Associated With Increased Risk of Back Pain in Multiple Sequential Logistic Regressions Among Colorado Farmers, 1993–1996 OR (95% CI) Characteristics Gender Male
Model 1
Model 2
Model 3
1.37 (0.96–1.95)
Model 4
1.58 (1.10–2.28)
1.15 (0.67–1.95)
Female Age in years 20–29
Referent
Referent
Referent
2.75 (1.02–7.40)
3.09 (1.13–8.40)
2.64 (0.91–7.70)
30–39 40–49 50–59
1.55 (0.89–2.68) 1.25 (0.77–2.03) 1.06 (0.65–1.75)
1.67 (0.95–2.92) 1.24 (0.76–2.05) 1.08 (0.65–1.79)
1.40 (0.73–2.67) 1.12 (0.65–1.90) 1.09 (0.65–1.84)
Referent
Referent
Referent
0.90 (0.59–1.39) 1.15 (0.75–1.79) Referent
0.85 (0.55–1.32) 1.16 (0.74–1.81) Referent
0.83 (0.53–1.30) 1.14 (0.72–1.78) Referent
Referent 0.75 (0.24–2.29) 0.97 (0.51–1.83) 1.16 (0.84–1.91)
Referent 0.75 (0.24–2.33) 0.94 (0.49–1.81) 1.20 (0.79–1.83)
Referent 0.76 (0.24–2.43) 0.94 (0.49–1.83) 1.16 (0.76–1.78)
3.96 (2.37–6.60) Referent
4.02 (2.40–6.74) Referent
3.68 (2.23–6.09) Referent
1.47 (0.88–2.44) 0.93 (0.50–1.74) Referent
1.66 (1.17–2.36) Referent Referent
Referent 1.58 (0.86–2.93) 1.18 (0.63–2.21)
Referent 1.62 (1.14–2.30) Referent
60⫹ Years of school 12 or less 13–15 16 or more Years of cigarette smoking Nonsmoker 1–15 16–25 25⫹ Depression Yes No Occupation Farming or ranching Home making Other Years employed in agriculture 1–9 10–29 30⫹ Primary cash crop Field and crop production Animals and livestock All others
ever, the positive association between depression status and back pain episodes warrants psychosocial factors being investigated in future studies of the farming population. This is of particular importance because a number of studies have recently reported a high risk of depression among farmers [Stallones, 1990; Stallones et al., 1995; Kidd et al., 1996; May, 1998]. It is biologically plausible that age is an important factor in the development of back disorders and should be included in multivariate modeling procedures [Dempsey et al., 1997]. Age has been reported to be associated with back pain [Bernard, 1997; Kraus et al., 1997; Dempsey et al., 1997].
Referent 0.94 (0.65–1.37) 1.31 (0.37–4.71)
However, the direction of the purported association is not consistent across these reports. In some of the studies, the risk of back pain episodes was higher with old age, while in other studies rates were higher in younger workers. Our results demonstrate that the occurrence of back pain episodes decreased with increasing age, with people age 20–29 having a significantly higher risk of back injury. But when adjusted for years of employment in agriculture, the age effects became statistically nonsignificant, suggesting that age may be confounded with other risk factors, as shown by Dempsey et al. [1997]. There is also the possibility that the age effects seen in this study were due to the ‘‘healthy
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worker effect,’’ with older farmers representing a cohort who did not experience severe back pain when they were young, and therefore were more likely to remain in farming. Further work is needed to delineate the relationship between psychosocial factors, agricultural activities, and back pain in the farming population. In particular, in order to prevent serious problems with back pain for this working group, the work practices related to lifting and repeated activities need to be further evaluated. If lifting is a significant problem, potential solutions may include packaging of materials in smaller quantities, use of lifting devices, or other workplace modifications such as avoiding the storage of heavy items above floor level.
Deyo RA, Cherkin D, Conrad D, Volinn E. 1991. Cost controversy, crisis: Low back pain and the health of the public. Annu Rev Public Health 12:141–156.
ACKNOWLEDGMENTS
Heliovaara M. 1993. Risk factors of low back pain — A review. In: Jayson EE, Pope MH, Porter RW, editors. Advances in idiopathic low back pain. Vienna: Blackwell.
We thank the interviewers for data collection and Yalin Chiu for data analysis.
Kaplan RM, Deyo RA. 1988. Back pain in health care workers. Occup Med 3:61–73.
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