Attributable fraction of work accidents related to occupational noise exposure in a Southeastern city of Brazil Fração atribuível de acidentes do trabalho decorrentes da exposição ao ruído ocupacional em cidade do Sudeste do Brasil

Noise is the most frequent type of occupational exposure and can lead to both auditory and extra-auditory dysfunction as well as increasing the risk of work accidents. The purpose of this study was to estimate the attributable fraction of work accidents related to occupational noise exposure in a medium-sized city in Southeast Brazil. In this hospital-based case-control study, including 600 cases and 822 controls, the odds ratio of work accidents (controlled for several covariables) was obtained classifying occupational noise exposure into four levels and determining the prevalence at each level. Based on these data, the calculated attributable fraction was 0.3041 (95%CI: 0.23410.3676), i.e., 30% of work accidents in the study area were statistically associated with occupational noise exposure. The authors discuss the causes of this association and the implications for the prevention of work accidents. Occupational Noise; Occupational Accidents; Attributable Risk Introduction Noise has accompanied humankind since time immemorial. Exposure to noise became more intense and prevalent, with a universal scope, when it began involving the work environment. Noise is currently considered the most common form of occupational exposure 1,2,3,4 and submits millions of workers to various injuries in activities like metallurgy, steel-making, carpentry, mining, transportation, and others. The principal harm caused by occupational noise is noise-induced hearing loss, an irreversible disorder with an insidious onset that deteriorates hearing and thus the communications capacity of exposed workers. Noise can also have extra-auditory repercussions (cardiovascular 5, endocrine 6,7, and gastrointestinal 8). Added to the above-mentioned auditory and non-auditory pathophysiological alterations, the specialized literature indicates that workers exposed to intense occupational noise present a twoto fourfold risk of accidents as compared to unexposed workers 9,10,11,12,13,14,15. Thus, noisecontrol and hearing conservation programs aim both to prevent exposure and hearing loss as well as to reduce the risk of work accidents 11,16. Given this scenario, the aim of this study was to estimate the attributable fraction of work accidents related to occupational noise exposure in a medium-sized city in Southeast Brazil. ARTIGO ARTICLE Dias A, Cordeiro R 1650 Cad. Saúde Pública, Rio de Janeiro, 23(7):1649-1655, jul, 2007 Method This research was part of a wider study aimed at improving workers’ health surveillance activities in the municipality (county) of Piracicaba, São Paulo State, Brazil, called Diagnosis and Control of Work Accidents in Piracicaba (DIATEP) 17,18,19. A hospital-based case-control study was conducted with local workers as the source population. The study focused on occupational noise exposure as a risk factor, among others, for work accidents. Case inclusion criteria were: residing in the city of Piracicaba, age 15-60 years, treatment for a typical work accident at the Emergency Department of the Piracicaba Orthopedics and Trauma Center (COT), and agreeing to participate in the study, signing an informed consent form. Inclusion criteria for controls were: belonging to the workforce (not unemployed), residing in the city of Piracicaba, age 15-60 years, treatment at the COT for any reason other than a work accident (or accompanying a patient receiving treatment there), and agreeing to participate in the study, signing an informed consent form. There is no reason to believe that if the controls had suffered work accidents during the study period they would have been treated in other hospitals. After explaining the study’s objectives and obtaining informed consent to participate, data were obtained from cases and controls by trained interviewers with a questionnaire on various occupational and non-occupational variables. Investigation of noise exposure was based on the following question: “What is the normal intensity of noise in your workplace?”, with four possible answers: “none”, “low”, “medium”, and “high”. In developing the analysis, investigation of the possible relationship between occupational noise exposure and the occurrence of work accidents involved adjustment of a multiple logistic regression model 20, in which the categorical and dichotomous response variable was the occurrence of an accident (control = 0, case = 1) and the predictive variable was the perception of exposure to occupational noise expressed by the worker, categorized according to the four levels mentioned above and controlled according to major occupational group 21, years of schooling, sex, and age bracket. The noise exposure levels were treated as dummy variables, with “non-exposure” as the baseline level. Further methodological details are provided in Dias et al. 22. Finally, calculation of the attributable fraction of work accidents related to occupational noise exposure used the usual equation 23,24,25, adapted by the authors of the current study to express the different exposure levels: where: AF = attributable fraction; i = different noise exposure levels used in the study; Pi = prevalence of workers exposed to noise level i in the source population; RRi = work accident incidence rate ratio (relative risk), comparing workers exposed to noise level i and workers unexposed to occupational noise in the source population. The prevalence rates of workers exposed to noise level i in the source population were estimated by the prevalence rates of these workers observed among the controls in the study. The relative risks (RRi) were estimated by the respective odds ratios (OR) obtained in the case-control study as cited above. Calculation of confidence intervals for the attributable fraction used a log transformation proposed by Walter 26, adapted by the authors of the current study: ( ) i i i i 112 2 0 0 12 i i i i 12 0 0 n m L = 1 1F A exp z + nn mm