Introduction Noise induced hearing loss (NIHL) is apreventable disease. However, the global burden of NIHL is increasing; especially in developing countries. The prevalence of NIHL among metal industry workers in Sub Saharan countries including Tanzania is not well documented.
Methods This study was conducted among male metal industry workers (Exposed, n=226) and Public Primary School teachers (Controls, n=110) between June 2016 and June 2017, in Dar es Salaam. The exposed were from four metal industries (Factory A, n=65; B, n=45; C, n=53; D, n=63). Hearing thresholds at 0.5, 1, 2, 3, 4, 6 and 8 KHz were examined using Interacoustic AD 226 audiometer. NIHL was defined as hearing threshold levels>25 dB in either ear at 3, 4 and 6 KHz. The WHO classification of hearing loss was used.
Results The prevalence of NIHL among exposed was 50% and 47% in the right and left ear, respectively. The highest prevalence was found in factory B(71% and 62%), followed by D(48% and 54%), A(48% and 48%), and the lowest in factory C(37% and 25%) in the right and left ear, respectively. The proportion of mild, moderate and severe NIHL in the right and left ear was 80% and 79%, 20% and 18%, 0% and 2%, respectively.
Among controls, the prevalence of NIHL was 31% and 28% in the right and left ear, respectively. The proportion of mild, moderate, severe NIHL in the right and left ear was 86% and 76, 11% and 15%, 3% and 0%, respectively. Nine percent of the controls had profound NIHL in the left ear and none among exposed.
Discussion We found high prevalence of NIHL among Tanzanian metal industry workers. Further studies on noise exposure and the determinants for reduced hearing are needed. Establishment of a hearing conservation program in the metal industries seems to be important.
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