This study results imply that MSDs are prevalent among study participants and a considerable number of WCs report moderate to high risk of persistent musculoskeletal pain. Factors significantly associated with the risk of chronic musculoskeletal pain include age, gender, work hours, work shift, several work postures and psychological conditions one week before the survey.
The prevalence of musculoskeletal pain among waste collectors
Musculoskeletal pain is very common among waste collectors in this study. Three fourth of them experienced pain in at least one body region by the time of the survey (74.4%), which was a higher percentage than what was reported by other studies among WCs in low and middle income countries with similar settings like Vietnam (44.7%-73.5%) (8, 9, 25). Lower back, neck, shoulders,forearms and upper back were the most affected body regions among WCs in this study. Other studies on WCs also reported that MSDs most occurred in the lower back (9, 10), upper limbs (9, 11) and shoulders (10). The manual waste collection process involves whole body movements. Lower back however, bears the highest amount of impact (1). Moreover, waste collecting job requires workers to stay in poor postures such as standing, moving, twisting the body, and sweeping for a long time which mainly affect the back, legs and hands, resulting in high MSD prevalence in said body parts. Continuous exposure to a variety of awkward postures might triggered the onset of musculoskeletal pain at multi-body sites (60.5%). Comparing with other occupations, the prevalence of multi-site MSDs among WCs in this study was also higher (5, 10). Within our knowledge, this study is the first attempt to examine the risk of long term disability due to musculoskeletal pain among waste collectors. The remarkable proportions of WCs with chronic pain and WCs with moderate to high risk of persistent MSDs emphasize the importance of prompt measures to improve current working conditions.
Factors related to the risk of persistent MSDs
Our results are in line with studies among working population, which reported the variance of MSDs among different gender and age groups (4, 5, 7), Being a female is often described as a "risk factor" for musculoskeletal disorders with higher prevalence of MSDs among women compared to men (22). Because of different physical strength in musculoskeletal system, the negative impact of the same physical labor is generally greater on females than males. In addition, older age and longer work experience contribute to the increased impacts of long-term exposure to occupational hazards, resulting in higher prevalence of MSDs among older workers (22). This results imply the need of support at work for female waste collectors and workers in their older age to prevent the risk of chronic MSDs and reduce any compensated cost MSDs might cause.
Regarding work organization, longer working hour significantly associated with a higher risk of persistent MSDs (OR 2.35, 95%CI 1.12 – 4.92) and WCs working at night reported less MSD complaint (OR 0.48, 95%CI 0.26-0.92). This results is quite exceptional because among work shifts, night shift (shift 3) has the most strenuous work. At night, WCs are exposed to higher level of psychological stress due to sleep deprivation, harsher climatic conditions (e.g. too wet or too cold) and fatigue. Moreover, the work shift only ends when all the garbage of the city has been collected and transported to the processing plant. Hence, sometimes work hour exceeds the regulation of 8 hours per shift. By the time of this survey, WCs with existed musculoskeletal problems might be scheduled to day shift since their physical health conditions were not suitable for night shift. Future longitudinal studies should be conducted to better identify the association between shift work and the risk of persistent MSDs among WCs.
No significant association is observed between the risk of persistent MSDs and exposure to physical work environment such as sunlight, heat, coldness and wetness. This result is different from findings of other studies. Magnavita et al. (19) in their study on hospital workers reported that exposure to temperature and light increased the risk of MSDs in the upper limbs (OR = 1.92 and 1.68, respectively). That study also found that temperature elevated the risk of MSDs in the lower back (OR = 1.31) (19).
Our study found that longer duration of unfordable postures (e.g. the neck/back bent for a prolonged time at an angle of over 45º without supportive equipment, medial rotation while walking and carrying >5kg with one hand) would elevate the risk of persistent MSDs. Empirical evidence was available to support the association between the increased risk of MSDS and poor working postures, quick motion and continuous bending or twisting while carrying or lifting heavy objects (1, 7, 10, 26).
Psychological stress, anxiety and job satisfaction could be an indicator of persistent MSDs. Mental stress diverts resources spent on attention, and can lead to fatigue and injury (1, 19). Study reported the significantly higher prevalence of depression, sleep disorders and occupational accidents among workers who had MSDs compared to those who did not (27). It is increasingly evident that addressing psychological factors impacting workers, is crucial for prevention of persistent MSDs.
Limitations of this study
We recognize several limitations of the current study. First, application of self-reported health conditions and work conditions could create a certain level of bias on the prevalence and level of persistent MSDs among the investigated participants. Second, it is not possible to create the causal relationship between demographic and work conditions and the persistent MSD with the cross-sectional study design in this paper. Third, generalization of the study results is limited to companies with similar work conditions, not all waste collectors in Vietnam Hence, future studies should consider more robust study design such as cohort or randomized control trial to evaluate the impact of work conditions on MSD among waste collectors in particular and different groups of occupation in general. Future studies also should include participants from different companies to enable the generalization of study results to broader population. However, this is the first paper reporting the risk of persistent MSDs among waste collectors in Vietnam, using the ÖMPQ.