Risk factors for back injury in 31,076 retail merchandise store workers

Risk factors for work-associated strain or sprain back injuries were investigated in a cohort of 31,076 material handlers from 260 retail merchandise stores in the United States. The workers studied were those with significant material-handling responsibilities - daily lifting and movement of merchandise. Workers in jobs with the greatest physical work requirements had an injury rate of 3.64 per 100 person-years versus 1.82 in workers with lesser work requirements. The unadjusted injury rate for males was 3.67 per 100 person-years compared with 2.34 per 100 person-years for females, but the excess for males was confounded by higher physical work requirements for men in the stocker/receiver job category. The injury rate ratio for short versus long duration of employment was 3.53 (95% confidence interval: 2.90, 4.30); for medium versus long duration of employment, it was 1.38 (95% confidence interval: 1.18, 1.62). The elevated rate ratios were maintained when the data were stratified by subsets with different rates of turnover. The results suggest that workers with the greatest physical work requirements and those with the shortest duration of employment are at the highest risk of back injuries. However, selection forces causing worker turnover within this cohort of active workers are not well characterized and have the potential to bias the measures for time-related factors such as duration of employment.