Carpal tunnel syndrome (CTS) is a common condition with an estimated prevalence in the general population of 2.7% and healthcare costs in the United States exceeding $500 million per year.(1, 2) Typical symptoms include numbness, tingling, and pain in the palmar and lateral aspects of the hand; and weakness of hand muscles may occur as the condition progresses. It is thought to result from chronic compression of the median nerve as it passes through the rigid carpal tunnel in the wrist.(3) Therefore, those who perform manual labor involving repetitive wrist movement are at increased risk for the development of CTS, with reported prevalence of 7.8% in occupations involving assembly lines, such as slaughterhouse workers.(4) CTS is a leading cause of workers’ compensation claims and results in significant lost time and productivity in manual workers.(5)

Poultry processing involves strenuous and repetitive work, with workers at risk for overuse injuries.(6, 7) Live birds are received and then passed through a production line that requires workers to hang, kill, pluck, clean, eviscerate, cut, package, and box poultry parts at a rapid pace, and workers also clean and repair equipment, assemble boxes, and move pallets of packaged poultry.(8, 9) Potential risk for overuse injuries such as CTS exists with each of these occupational duties.

Across the United States, the poultry processing workforce has become largely composed of immigrants, with Latinos making up a large proportion.(6, 10) This group bears a disproportionate burden of workplace injury because of language and cultural barriers that prevent workers from receiving health and safety measures, as well as reluctance of workers to complain about work conditions.(11–13) Therefore, this study was conducted to examine the prevalence of CTS in Latino poultry processing workers and to compare this prevalence to Latinos in other manual labor positions. In addition, it was designed to assess characteristics that may increase the risk of CTS in poultry processing workers.

The demographic characteristics for the poultry processing workers and non-poultry workers are described in Table 1. Poultry workers were older than non-poultry workers (36.3 vs. 32.7 years, p = < 0.0001). The poultry group also weighed less and had a trend toward being shorter, which resulted in similar BMIs between the groups (28.6 in poultry and 29.2 in non-poultry, p = 0.1739). The groups were similar in the percentage of women and the distribution of spoken languages, and the poultry workers had less formal education (p = 0.0354).

The prevalence of CTS was higher in the poultry workers than the non-poultry workers (p < 0.0001), and this held true when the prevalence was evaluated by considering either the wrist or the worker as an individual unit for statistical analysis (Table 2). When wrists were assessed, 6.5% of the poultry worker wrists had definite CTS compared to 2.4% for non-poultry, and 48.0% of the poultry worker wrists had possible or definite CTS compared to 26.3% of non-poultry. When individuals were assessed, 8.7% of the poultry workers had definite CTS compared to 4.0% for non-poultry, and 59.2% of the poultry workers had possible or definite CTS compared to 35.0% of non-poultry. The adjusted odds ratio (controlling for age, BMI, and gender) for the prevalence of CTS was 2.51 (95% CI of 1.80 to 3.50) in poultry workers compared to non-poultry workers (Table 3). Table 3 also shows the increased risk of CTS with increasing age (odds ratio of 1.04, 95% CI 1.02 to 1.06) and BMI (odds ratio of 1.08, 95% CI 1.05 to 1.12), and that gender was not associated with an increased risk of CTS.

In the 287 poultry workers (574 wrists), greater age was seen in those with CTS compared to those with possible or no CTS (Table 4). Table 4 also shows that job category predicted the prevalence of CTS, with those in category 1 (packing, sanitation, chilling, and other) having less CTS than those in category 4 (multiple jobs) and a trend towards less than those in category 2 (cutting, eviscerating, wash-up, trimming, and deboning). Comparisons of CTS prevalence in job categories two, three, and four to each other did not approach statistical significance.

In this study, multiple analyses were performed, both at the level of the wrist and the individual, and the prevalence of CTS was consistently higher in Latino poultry processing workers compared to other Latino manual workers. The prevalence of CTS in the non-poultry manual workers (2.4% of wrists and 4.0% of individuals) was similar to the prevalence in the general population found in previous studies,(1) whereas the odds of CTS was more than 2.5 times greater in the poultry processing workers. It is unlikely that factors other than occupational tasks accounted for the difference in CTS prevalence, as the two groups were similar in BMI and gender distribution, and the poultry workers were actually younger in age (older age is associated with an increased risk of CTS). Therefore, the repetitive and strenuous nature of poultry processing work likely resulted in the increased CTS prevalence. This is supported by the finding that poultry workers that performed tasks requiring the most repetitive hand manipulation (cutting, eviscerating, washing, trimming, deboning and multiple tasks) had more, or a trend toward more, CTS than those performing other tasks along the production line (packing, sanitation, chilling, and other).

The actual prevalence of CTS in the poultry workers depends on the parameters used to define CTS. The most sensitive combination of symptoms and nerve conduction studies results in 48% of the wrists and 59.2% of the individuals categorized as possible or definite CTS, whereas the most specific combination of parameters results in 6.5% of the wrists and 8.7% of the individuals categorized as definite CTS. The true prevalence certainly lies somewhere between these values, but no matter which definition is used, it is clear the prevalence of CTS is high in this population.

Some limitations exist in this study. First, defining CTS in a large population such as this can be challenging, as it is not feasible to obtain a detailed history, physical examination, and electrodiagnostic study on each participant. We opted to use a combination of self-reported symptoms and sensory nerve conduction studies to assess for CTS. While this is less thorough than the evaluation performed by a meticulous clinician on an individual patient, it is at least as complete as other studies in which large populations were screened for CTS.(4, 16, 17) The second limitation occurred when trying to categorize poultry workers by tasks, as many workers performed multiple tasks along the production line on a weekly basis. It was decided that a worker would only be categorized to a task if they performed it greater than 50% of the time, and otherwise they were placed into the “multiple tasks” category. This strategy allowed most workers to be categorized, but many participants performed tasks on a weekly basis other than the one to which they were grouped. For this reason, it is challenging to identify very specific tasks associated with a higher prevalence of CTS. While these limitations are present, they are relatively minor and the strengths of the study, including a large sample size, relevant comparison group, and systematic approach to CTS diagnosis outweigh the limitations.

The high prevalence of CTS in this population indicates that measures should to be taken to reduce the amount of repetitive strain on the hands and wrists of poultry processing workers and to increase early identification of CTS. Since some poultry processing tasks (such as packing, sanitation, and chilling) were associated with less CTS, one consideration would be for all workers to rotate through these tasks on regular intervals. Other interventions, such as an emphasis on ergonomics, should also be considered, although the data supporting this type of intervention are limited.(18) Finally, increased surveillance for the development of CTS in this population could result in earlier identification and treatment.(19)