Comparison of the hearing levels of Nigerian textile workers and a control group

The comparative auditory performance of 61 industrially exposed male textile workers (noise level, 90 dBA - 115 DBA) and 90 age matched control subgroup was determined by means of a manual Diacoustic As-60 audiometer. The audiograms of both the exposed and control subgroups were convex upwards, indicating that the hearing sensitivity of the Nigerian, black subjects increased with frequency, a finding that is in contrast with that reported elsewhere for white subjects. The impact of ageing on the hearing of both the exposed and control groups was minimal and not statistically significant, supporting an earlier study that found no age related hearing loss among South Sudanese blacks. The impact of noise on the hearing of the subjects was, however, very marked. In each age group and at each frequency, the hearing thresholds of the exposed subjects were significantly higher (0.01 greater than p less than 0.005) than those of the control group. After seven years of continuous employment, the rate of hearing loss attributable to noise, among the exposed group, increased from 2.17 dB to 11.67 dB per year of employment compared to an increase of - 0.64 dB to 1.82 dB in age induced loss per year of age difference in the same group. It seemed the exposed subjects experienced a seven year hearing threshold of 30 dB irrespective of statistically significant differences in age (p less than 0.005) and duration of employment (p less than 0.01) of the groups covered by this period. After this "latency period" the hearing loss increased rapidly.