Study Design. Four-year prospective cohort study.
Objective. To find the incidence of sick leave because of neck and shoulder pain (NSP) in industrial workers, and its association with work and lifestyle risk factors.
Summary of Background Data. Longitudinal studies to investigate NSP incidence and risk factors are rare, and even fewer have been conducted in middle- and low-income countries.
Methods. After inviting all full-time employees of an Iranian car manufacturing company with 18,031 employees to participate in a baseline study, they were followed for 4 years. New episodes of sick leave because of NSP have been calculated based on sickness absence registration between the years 2003 and 2007. The incidence was compared for participants and nonparticipants.
The association between sick leave, physical, and psychosocial risk factors at work, and previous self-reported NSP, was calculated for the remaining population of baseline participants (12,184 employees) during a 4-year follow-up.
Results. During a 4-year follow-up of study subjects for the remaining participants of the baseline study, the incidence of sick leave was 0.8% (98 sick leave cases in 12,184 employees). For nonparticipants this incidence was 4.2% (130 cases in 3127 employees). In the final regression model for sick leave cases, the remaining factors for potential physical risk factors were repetitive work and sitting positions at work; for psychosocial factors unattractive work was the only significant remaining factor.
Conclusion. The incidence of NSP based on sick leave is definitely very low compared with previous studies in high-income countries. This incidence varies between participants and nonparticipants. Risk factors for sick leave differ from risk factors for self-reported pain. A young population, job security, the insurance system, different health behaviors, and healthy worker bias, are all factors that may affect the results, and sick-leave as an outcome must be interpreted with more caution in middle- and low-income countries.