This study results reveals an extremely high prevalence of MSDs among participated WCs. Significant related factors include work shift, several work posture and psychological conditions one week before the survey.
Situation of MSDs
In this study, 100% participated WCs experienced MSDs in at least one body region by the time of the survey, which is a higher percentage than what several previous studies among WCs concluded (43.2-92.5%) (8-11). The difference in the findings of this study compared to previous studies might be attributable to the heterogeneity in the characteristics of study participants, working conditions, climatic condition of Vietnam compared to those in other countries, especially the proportion of gender, age and years of work experience (8, 9). This could be explained by the higher number of female participants (89.7%) since they experience a higher prevalence of MSDs compared with their male counterparts (Örebro mean score: 98.5 in women versus 88.5 in men) in this study. Studies shows that being a female is often described as a "risk factor" for many musculoskeletal disorders with higher prevalence of MSDs among women compared to men (14) because of different physical strength in musculoskeletal system. In addition, age and years of work experience played an important roles in the elevated risk of MSDs in this study because these conditions increased the effects of cumulative exposure of occupational hazards, resulting in higher prevalence of MSDs among older workers (14). This results imply the need of support at work for female waste collectors, workers in their older age or with longer years of work experience to prevent the risk of persistent MSDs, protect workers’ health and reduce any compensated cost MSDs might cause. The MSD prevalence in this study was even higher than that of studies in other occupations such as lobster catching (82.3%) (4), physiotherapists (89%)(2), cattle slaughterers (88.2%) (5), carpet weavers (87.6%) (6) and dentists (69%) (7). This indicated that the waste collection job might result in higher risk of MSDs among WCs in comparison with other occupations.
Lower back, neck, shoulders, forearms and upper back were the most frequently affected body sites in this study. Other authors also reported that MSDs most occurred in the lower back (7, 9, 10), upper limbs (9, 11) and shoulders (10). However, the prevalence of MSDs in the lower extremity in this study was lower than that of the study among Iranian waste collectors (7, 10). The manual waste collection process involves most body regions. Lower back however, bears the highest amount of impact (1), which explains the high prevalence of low back pain. Moreover, waste collecting job required workers to frequently change their posture (standing, moving, twisting the body, and sweeping) which mainly affected the back, legs and hands, resulting in high risk of MSDs for said body parts. This also explained the high prevalence of MSDs at multi-body sites (81%). When compared to studies among workers in different occupations, the prevalence of multi-site MSDs among WCs in this study was also higher (2, 4, 7, 8, 10).
Factors related to persistent MSDs
Regarding MSD related factors, the severity level of MSDs were higher among female compared to male workers (p<0.05). This might be explained by the biological differences between men and women. The negative impact of the same act of physical labor is generally greater on females than males, which has been discussed above. The difference in the prevalence of MSDs between males and females was consistent across different occupations (3, 4, 6). Among demographic and work organization characteristics, no significant association between education level, age, years of service, work hours and MSDs was found, excluding the significant association between the work shift during the last three months and the Örebro mean score (p <0.01). Among work shift, night shift (shift 3) was rated as the most strenuous work. At night, WCs were exposed to higher level of psychological stress, harsher climatic conditions (e.g. too wet or too cold) and fatigue. Moreover, their work hours during night shift only ends when all the garbage of the city has been collected and transported to the processing plant. Hence, sometimes it exceeds the regulation of 8 work hours per shift. In this study, WCs with higher level of MSDs might be scheduled to day shift since their physical health conditions were not suitable for night shift by the time of the survey. Future longitudinal studies should be conducted to better identify the association between shift work and risk of MSDs.
In our study, no significant association was found between exposure to physical work environment and MSDs. This result was different from findings of other studies. Magnavita et al. (13) 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) (13).
Among all investigated unfavorable postures and tasks, this study found the significant association between the duration of the neck bent for a prolonged duration at an angle of over 45º without supportive equipment, kneeling, and medial rotation while walking, and the Örebro mean score, indicating that longer duration of unfordable postures would elevate the risk of persistent MSDs. This results were consistent with other studies which reported that factors including remaining in harmful postures for a prolonged duration, quick motion and continuous bending or twisting while carrying or lifting heavy objects increased risk of MSDs (1, 6, 10, 22).
Psychological stress was also found to be one risk factors of MSDs. Mental stress diverts resources spent on attention, and can lead to fatigue and injury (1, 13). Various studies suggest that the prevalence of depression, sleep disorders and occupational accidents were higher among workers who had MSDs compared to those who did not (23). It seems increasingly evident that addressing psychological factors impacting workers, is crucial for prevention of 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 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 to describe the situation of persistent MSDs among waste collectors in Vietnam, using the ÖMPQ.