The Prevalence of Notched Audiograms in a Cross-Sectional Study of 12,055 Railway Workers

Objective: Noise-induced hearing loss (NIHL) is one of the most
reported occupational diseases internationally. The occurrence of audiometric notches is emphasized in both American and European guidelines
for the diagnosis of NIHL. The aim of this study was to describe the
prevalence of notched audiograms among railway personnel with and
without noise exposure to better assess the usefulness of such notches
in the diagnosis of NIHL.
Design: The most recent audiogram from 1994 to 2011 of a total of
12,055 railway workers, age 20 to 65 years, was obtained from the medical records of the occupational health service of the Norwegian State
Railways (NSB). The prevalences of three types of notched audiograms,
Coles notch, notch index, and 4kHz notch, were computed, in relation to
age, sex, and occupational noise exposure.
Results: Coles notch in either ear was found in 63% of the male railway
maintenance workers, exposed to noise levels of 75 to 90 dB(A), compared with 53% of the non-noise exposed (<70 dB(A)) traffic controllers (p < 0.001). The corresponding figures for the 4kHz notch were 31% versus 21% (p < 0.001). For the notch index, 61% of the exposed and 51% of the controls had a notched audiogram (p < 0.001). [...]