Prevalence of tinnitus in noise-exposed workers and its influencing factors

Background  Tinnitus is a common symptom in workers exposed to noise, and no specific treatment is available yet. Paying attention to the influencing factors of tinnitus is very important to prevent tinnitus.

Objective  To investigate the situation of tinnitus among noise-exposed workers and its influencing factors.

Methods  Using a cross-sectional study design, 1011 noise-exposed male workers in Hangzhou were studied. Tinnitus status, age, education, personal protection, smoking history, drinking history, and family history of the participants were surveyed by questionnaires. Binaural pure tone hearing threshold test was performed on all study subjects. The environmental noise in the workplace was measured. The relationships of tinnitus with noise exposure intensity, noise exposure time, noise exposure category, cumulative noise exposure, and wearing hearing protectors among the noise-exposed workers were analyzed by logistic regression.

Results  The prevalence of tinnitus among the noise-exposed workers was 36.1%. The mean hearing thresholds at 500, 3000, 4000, and 6000 Hz in the right and left ears were higher in the tinnitus group than in the non-tinnitus group (P<0.05); the hearing threshold at 2000 Hz in the right ear was higher in the tinnitus group than in the non-tinnitus group (P<0.05). There was no statistically significant difference between the two groups in the prevalence of monaural speech-frequency hearing loss or monaural high-frequency hearing loss (P>0.05). The on-site noise intensity was divided into three groups: ＜85, 85-＜95, and ≥95 dB(A); the prevalence of tinnitus in the three groups was 19.6%, 40.5%, and 66.7% respectively. The years of noise exposure was divided into three groups: ＜1, 1-＜5, and ≥5 years; the prevalence of tinnitus in the three groups was 17.9%, 34.0%, and 45.4% respectively. The cumulative noise exposure was divided into six groups: ＜80, 80-＜85, 85-＜90, 90-＜95, 95-＜100, and ≥100 dB(A)·year; the prevalence of tinnitus in the six groups was 6.8%, 25.0%, 31.0%, 39.6%, 43.1%, and 46.7% respectively. The prevalence of tinnitus was higher in the non-stationary noise group (42.5%) than in the stationary noise group (26.8%) (χ²=26.18, P<0.01), and the prevalence in the group without or with hearing protection was 39.7% and 35.5% respectively. The results of logistic regression showed that workers exposed to higher intensity, longer noise exposure, higher cumulative noise exposure, and non-stationary noise (reference: stationary noise) resulted in a higher risk of tinnitus (P_trend<0.01 or P<0.01); workers wearing of hearing protection device versus those not showed a lower risk of tinnitus (P<0.05).

Conclusion  Higher intensity, longer exposure to noise, and more cumulative noise exposure associate with a higher risk of tinnitus. Wearing hearing protective device can reduce the risk of tinnitus. Tinnitus in noise-exposed workers can precede the presentation of abnormal hearing loss.