The dose–response relationship between noise-induced hearing loss and cumulative noise exposure adjusted by the effect of hearing protection devices among workers in Southern China

The noise exposure levels of workers wearing hearing protective devices (HPDs) depend on ambient noise and the protective effect of hearing protectors. This cross-sectional study aimed to adjust for cumulative noise exposure (CNE) based on the effective protection of hearing protection devices and explore the dose-response relationship between noise-induced hearing loss (NIHL) and adjusted cumulative noise exposure. A questionnaire was used to acquire the basic characteristics and occupational information of noise-exposed workers. Individual noise dosimetry, individual fitting tests, and pure-tone audiometric tests were performed to assess workers' noise exposure levels, HPDs' sound attenuation, and hearing status. A total of 714 workers participated in this study. Four hundred seventy-three participants wore foam earplugs and 241 wore pre-molded earplugs. The median Personal Attenuation Rating (PAR) was 13.0 dB. The median PAR' (the PAR after combining the earplugs usage time) was 8.0 dB. Thirty-one percent of the workers wore earplugs properly during noise exposure and they tended to possess a greater PAR. The median L_Aeq,8h was 94.1 dB (A) and the median unadjusted cumulative noise exposure was 102.3 dB (A)· year. The PAR'-adjusted CNE (CNE_P) was 91.3 dB (A)·year. A total of 161 workers (22.5%) with hearing loss were identified. There was an obvious trend between the prevalence of NIHL and CNE_P (χ_trend² = 31.9, p < 0.01). The Wald values of the CNE and CNE_P logistic regression models were 4.0 and 14.1, respectively. Furthermore, the curve slope of the CNE_P was steeper than that of the unadjusted CNE. The CNE_P can represent the noise exposure level among workers wearing hearing protectors more accurately and has an apparent dose-response relationship with the prevalence of NIHL. For workers utilizing hearing protection devices, wearing them properly and consistently in the workplace is recommended. Assessing noise exposure based on the protective effects of hearing protectors is also essential. Additional studies are needed to quantify the impact of behaviors associated with the improper use of hearing protection.