Occupational exposures and health-related quality of life in the Manaus Metropolitan Region, Amazonas State, Brazil: a cross-sectional study

We aimed to investigate the association between occupational exposures and health-related quality of life among both informal and formal workers in the Brazilian Amazon. We conducted a cross-sectional study with working adults in the Manaus Metropolitan Region, Amazonas State, in 2015. Participants were selected through a three-step probabilistic sampling. The primary outcome was the health-related quality of life indicator, measured by the Brazilian validated version of the European Quality of Life 5-Dimensions 3-Levels (EQ-5D-3L) tool. Adjusted multivariate analysis was performed by Tobit regression and considered the complex sampling design. Results were converted to odds ratio (OR). Out of the 1,910 working individuals from the sample, 60.2% were formal workers. Informal workers were significantly more exposed to occupational risks than formal workers (p ≤ 0.05). Mean utility score for informal and formal workers was 0.886 (95%CI: 0.881; 0.890). Quality of life of informal workers was negatively impacted by exposure to noise (OR = 1.28; 95%CI: 1.13; 1.52), occupational stress (OR = 1.95; 95%CI: 1.65; 2.21), and industrial dust (OR = 1.46; 95%CI: 1.28; 1.72), while formal workers were negatively associated with exposure to chemical substances (OR = 1.58; 95%CI: 1.28; 1.87), noise (OR = 1.40; 95%CI: 1.23; 1.65), sun (OR = 1.65; 95%CI: 1.09; 1.40), occupational stress (OR = 1.65; 95%CI: 1.46; 1.87), biological material (OR = 2.61; 95%CI: 1.72; 3.97), and industrial dust (OR = 1.46; 95%CI: 1.28; 1.65). Exposure to occupational risks among workers from the Manaus Metropolitan Region was high, affecting both informal and formal workers. Brazilian policies need to be enforced to reduce the impacts on quality of life among workers in this region. Occupational Risks; Occupational Exposure; Occupational Health; Quality of Life Correspondence G. M. B. Tiguman Rua Cândido Portinari 200, Campinas, SP 13083-871, Brasil. gustavo.tiguman@gmail.com 1 Universidade Estadual de Campinas, Campinas, Brasil. 2 Universidade de Sorocaba, Sorocaba, Brasil. doi: 10.1590/0102-311X00074520 Cad. Saúde Pública 2020; 36(12):e00074520 COMUNICAÇÃO BREVE BRIEF COMMUNICATION This article is published in Open Access under the Creative Commons Attribution license, which allows use, distribution, and reproduction in any medium, without restrictions, as long as the original work is correctly cited. Tiguman GMB et al. 2 Cad. Saúde Pública 2020; 36(12):e00074520 Introduction It is estimated that approximately 2.3 million deaths related to occupational diseases occur every year worldwide, mainly due to cancer (32%), work-related circulatory diseases (23%), communicable diseases (17%), and occupational accidents (18%) 1. In 2013, 154,240 cases of work-related diseases and injuries were reported in Brazil 2. Between 2008 and 2013, an increase in the proportion of informal workers among the reported cases was observed in the country 2. Informal workers showed worse self-reported status, greater difficulty in accessing healthcare services, and less interest in seeking healthcare services when compared to formal workers in a nationwide survey from 2008 3. Studies evaluating the occupational risks and quality of life for both formal and informal workers are scarce in Brazil. The aim of this study was to assess the association between occupational exposures and health-related quality of life among informal and formal workers in the Brazilian Amazon.

In 2013, 154,240 cases of work-related diseases and injuries were reported in Brazil 2 . Between 2008 and 2013, an increase in the proportion of informal workers among the reported cases was observed in the country 2 . Informal workers showed worse self-reported status, greater difficulty in accessing healthcare services, and less interest in seeking healthcare services when compared to formal workers in a nationwide survey from 2008 3 .
Studies evaluating the occupational risks and quality of life for both formal and informal workers are scarce in Brazil. The aim of this study was to assess the association between occupational exposures and health-related quality of life among informal and formal workers in the Brazilian Amazon.

Methods
This was a cross-sectional population-based study conducted in the Manaus Metropolitan Region, Amazonas State, Brazil, in 2015 4 .
This study specifically included the working population of a major survey, which selected adults (≥ 18 years) through a probabilistic three-step complex sampling design 4 . Participants were divided into two categories: formal and informal workers. Formal workers are those with formal employment relationship, which guarantees labor rights and social benefits, such as vacations, maternity leave, retirement, and unemployment support 5 . Informal workers are defined as individuals who develop their own economic activities and do not have any social security or formal relationships with an employer 5 .
The primary outcome was the health-related quality of life. Individual variables included: sex (male, female), age group (18-24, 25-34, 35-44, 45-59, ≥ 60 years old), socioeconomic classification (A/B, C1, C2, D/E, where A refers to the wealthiest and E, to the poorest 6 ), educational level (higher education or above, high school, middle school, elementary school or less), work type (informal/formal), and occupational exposure related to work activities (work in nocturnal periods, work for more than 24 consecutive hours, exposure to chemical substances, noise, sun, radioactive material, garbage, occupational stress, biological material, industrial dust).
Health-related quality of life was assessed by the European Quality of Life 5-Dimensions 3-Levels tool (EQ-5D-3L) 7 . It includes five dimensions (mobility, self-care, pain/discomfort, anxiety/depression, and usual activities). Each dimension can be scored in three levels (1 = no problems, 2 = moderate problems, and 3 = severe problems). Levels of quality of life were transformed into utility values using the conversion formula in accordance with the Brazilian valuation of EQ-5D-3L 8,9 . Data collection was performed through face-to-face interviews with trained interviewers using standardized questionnaires. The responses were registered in electronic tablets (Tab 3 SM-T110 Samsung Galaxy).
We used descriptive statistics to evaluate the sociodemographic characteristics of the working population and the results of each dimension of the EQ-5D-3L, stratified by formal and informal workers. We also calculated the means of the quality of life utility scores considering 95% confidence intervals (95%CI). Multivariate analyses were performed by Tobit regression adjusted by age group, socioeconomic classification, educational level, and the complex sampling design 10 . The Tobit regression model was chosen as it is suitable for censored or bounded data that can produce ceiling effect (i.e. inability to discriminate among high levels of health status) 11 , such as the EQ-5D-3L utility scores 12 . The utility scores were included as the latent dependent variables in the model. Significant associations were transformed into odds ratio (OR) using the following equation: ln(OR) = π/√3 x β 13 . To facilitate interpretation, the inverse of the OR was presented to indicate the association between occupational exposures and lower quality of life. Stata version 14.2 (https://www.stata.com) was used for the data analyses.

Results
Out of the 4,001 participants of the main population-based study, 1,910 were workers, of which 60.2% were formal workers. The majority of the individuals were men (66.6%), aged 25-44 years old (57.7%), part of the socioeconomic classification C (middle class; 58.3%), and with an educational level up to high school (51.8%; Table 1). Most occupational exposures were observed among informal workers, except for exposure to the sun and working for more than 24 consecutive hours. Significant differences between informal and formal working groups were observed in the following occupational exposures: working in nocturnal periods (p < 0.001), exposure to chemical substances (p < 0.001), noise (p < 0.001), sun (p < 0.001), radioactive material (p = 0.023), occupational stress (p = 0.009), and biological material (p < 0.001). Health-related quality of life scores for all five dimensions were mostly reported as good (without any problem). For formal workers, the mean utility score was 0.907 (95%CI: 0.899; 0.915); for informal workers, it was 0.882 (95%CI: 0.874; 0.889). The mean utility score for both informal and formal workers was 0.886 (95%CI: 0.881; 0.890). Informal workers reported better health statuses in mobility (96.1% vs. 92.8%) and pain/discomfort (63.7% vs. 56.6%) dimensions in comparison to formal workers. The dimensions with higher proportion of individuals with bad statuses were pain/discomfort and anxiety/depression ( Table 2).

Discussion
Informal workers were significantly more exposed to working in nocturnal periods, chemical substances, noise, radioactive material, occupational stress, and biological material, whereas formal workers were more frequently exposed to sun. Health-related quality of life was high among workers, similarly to the general population from the Manaus Metropolitan Region 9 .
Recall bias from the self-reporting model may have influenced the results as participants might not remember being exposed to certain occupational risks. Selection bias is also possible since only individuals who were present at their residences during the interview period were invited to participate in the survey. Although the EQ-5D-3L instrument is easy to apply and is currently used in different contexts worldwide for measuring quality of life, its discriminant ability is lower when compared to other specific instruments 14 . Relevant data such as physical activity, religious beliefs, Cad. Saúde Pública 2020; 36(12):e00074520 chronic diseases, fruit and vegetable consumption, and leisure time were not collected, which may play an important role on quality of life 15 .
The Brazilian Labor Reform approved by the National Congress in 2017, two years after this study was conducted, resulted in significant changes to the employment regulations by allowing employers to determine hiring conditions, use of workforce, and other social rights 16 . This process led to increased insecurity among workers, loss of labor rights, and reduced social protection 16 . Empirical evidence from after the implementation of the Labor Reform showed that this act probably impacted workers' health and quality of life 17 .
Exposure to noise in occupational settings was negatively associated with the quality of life of both informal and formal workers. A study conducted in 2015 in Belo Horizonte, Minas Gerais State, with professionals working in ambulances found that auditory (tinnitus, intolerance to intense sounds, and aural fulness) and nonauditory symptoms (irritability, headache, difficulty in talking in noisy environments, and sleep alterations) were frequent among these professionals 18 . Preventive measures should be adopted to reduce the risks and improve the quality of life of these workers.
Occupational stress was also a negative factor for the workers' quality of life. A cross-sectional study conducted in Pelotas, Rio Grande do Sul State, in 2012 with community health agents showed that 71% of the 181 professionals were in a state of stress resistance, 30.5% were in the alert state of stress, and 32.8% were in the stress state of exhaustion, which were confirmed by higher salivary cortisol levels. Depressive episodes were observed in 28.2% of the participants and low scores for quality of life were reported 19 .
Occupational exposure to biological materials and industrial dust were associated with worse quality of life among informal and formal workers. Healthcare professionals are particularly at increased risk of occupational exposure to biological materials since they are frequently in contact with body secretions and can be injured by handling sharp instruments, which may lead to microbiological infections 20 . A previous study conducted in Namibia from 2013 to 2014 with 307 workers from charcoal factories showed that exposure to dust was significantly associated with usual cough, usual phlegm, episodes of phlegm and cough, and shortness of breath 21 .
Exposure to chemical substances and to sunlight negatively affected the quality of life. Such exposures are risk factors for chronic noncommunicable diseases. A cross-sectional study carried out in 2014 with 545 civil construction workers from Cuiabá, Mato Grosso State, found that the odds of developing respiratory symptoms (e.g., cough) were higher for those exposed to chemicals, such as paint and hydrocarbon solvents 22 . A previous cross-sectional study conducted in 2017 with 348 outdoor workers (farmers, gardeners, and mountain guides) and 215 indoor workers (office employees) from Germany found an increased risk of developing non-melanoma skin cancer in outdoor professionals 23 .
Radioactive materials were positively associated with the quality of life of formal workers. Labor protection associated with contracts of workers involved with radiation activities in Brazil may explain these results. A meta-analysis from 2014 investigating the renal effects and carcinogenicity of occupational exposure to uranium in 71,114 workers found a significantly lower tumor risk in the case groups when compared to control groups, and the risk of nephrotoxicity was also not increased 24 . This finding contrasts with the results of a previous case-control study conducted in Shanghai, China, from 1987 to 1989, where a significant increase in the risk of leukemia was observed in workers who self-reported exposure to benzene, synthetic fiber dust, toluene, and radioactive materials 25 .

Conclusions
The exposure to occupational risks among the working population of the Manaus Metropolitan Region is high and affects both informal and formal workers. Quality of life was negatively associated with exposure to noise, occupational stress, industrial dust, chemical substances, sunlight, and biological materials. Health policies and labor rights should be protected and reestablished in Brazil to reduce health inequalities among informal and formal workers, as well as minimize potential risks associated with occupational exposure.