Effect of earplug use and factors associated with noise induced hearing loss among occupational workers in Guangzhou, China

Abstract

Background: Noise is one of the most important forms of environmental pollution among developed and developing countries. A report from UK National Study of Hearing estimated that around 440 million people suffer from noise induced hearing loss in EU countries with 1–1.6 million disability-adjusted life year lost. In China, the Second China National Sample Survey on disability in 2007 revealed that about 27.8 million people suffered from hearing impairment, and 73.4% of which (about 20 million) were diagnosed with disability. The prevalence of hearing impairment was estimated to be 2.1% in the general population, and increased to 11.0% among those aged greater than 65 years.

Objective: To find out the effect of earplug on noise induced hearing loss (NIHL), as well as understanding the source and exposure of noise in the industry, to estimate the prevalence of NIHL in factories with noise exposure, to analyze relationships between NIHL and age, sex, dose and duration of occupational noise exposure, type of work, use of hearing protection products, education level and other factors. Significant risk factors identified were used to provide evidence-based recommendations in prevention and control of NIHL.

Study Design: Retrospective, cross-sectional study

Method: A total of 1874 workers exposed to noise in a compressor factory in Guangzhou, China were included. Between September 2011 and January 2012, physical examination including a screening program of hearing loss, pure tone audiometry test were carried out among workers including information on age, sex, work types, noise exposure level, exposure time, as well as the questionnaire about earplug using status, status of using ear products report by company, smoking status, education level, discharge of ear, history of herpes zoster, history of using ototoxic drugs, history of ear surgery, family history of NIHL, systolic blood pressure, diastolic blood pressure. The outcome variable is the audiometric mean value which reflects hearing status of the subjects. Subgroup differences in mean value of audiometry were compared by independent sample t-test. Multiple linear regression and logistic regression models were used to evaluate associations between earplug use and NIHL, adjusted for other potential confounders. Factors associated with earplug use were also identified.

Result: 1873 workers took part in the study (both physical examination and questionnaire) The prevalence of NIHL is 381 (20.3%) from study, and an average noise level of 83.5 dB was detected in the factory across different types of working place. The pure tone audiometric mean value (PTA) is 26.7 dB with a standard deviation of 4.8. The mean PTA value for those using earplug is 25.81 dB, which was significantly lower than those not using earplug with a mean PTA value of 1.54 dB (p < 0.001). A 0.962 mean difference is detected between noncontinuous earplug usage group and continuous usage group.

Multiple linear regression model showed a dose response effect in use of earplug on NIHL, with an estimated mean PTA 1.49 dB (p-value <0.001) and 0.96 dB (p-value = 0.001) lower than those not using earplug at all. Hearing protective effect with part of dose response relationship is found in education level groups as well. Workers from technical school have a 5.974 dB lower of mean PTA, where the decrease is 3.909 dB in high school group, reference of primary level. Moreover, ever smokers show 1.557 dB higher on reference as nonsmoker. Other significant results can be found in family history of NIHL, ototoxic drug using, with statistical significant, respectively, with the direction of positive to NIHL, which shows harmful effect on workers’ hearing.

Multivariable logistic regression model is used to find out factors associated with earplug usage. In the model, higher education level is found to be associated with higher earplug usage, especially among participants from technical schools, with an adjusted odds ratio (AOR) of 34.07, whereas those from high school group have an AOR of 12.35.(With Primary school group being the reference group.) Workers whose daily tasks involve phosphorus board, punching press, compressor are found to have a relatively low percentage on earplug usage compliance, with AOR of 0.55, 0.41, 0.23 respectively. (Those from machine shops are used as the reference group.) The result is in accordance with their positive correlation on NIHL.

Conclusion: Use of earplug was found to be protective to NIHL. Factors such as education level, smoking status, discharge of ear, family history of NIHL and certain types of work were found to be associated with lower risk of NIHL. To protect hearing of the workers and reduce NIHL prevalence, provision of and education on hearing protection products and supervision of continuous use of earplug in noise exposed industry should be implemented. Occupational health monitoring to the enterprises should be enhanced by health sectors of Chinese government. Due to the limitation of retrospective design of this dissertation, further cohort studies are called for to provide stronger evidence of factors’ effect on NIHL.