Air pollution increases the risk of SSNHL: A nested case-control study using meteorological data and national sample cohort data

This study aimed to evaluate the impact of weather conditions and air pollution on the onset of sudden sensorineural hearing loss (SSNHL). The Korean Health Insurance Review and Assessment Service-National Sample Cohort (HIRA-NSC) from 2002 through 2013 was used. A total of 5,200 participants with SSNHL were matched 1: 4 for age, sex, income, region of residence, hypertension, diabetes, and dyslipidemia with 20,800 control participants. Meteorological data included daily mean temperature (degrees C), daily highest temperature (degrees C), daily lowest temperature (degrees C), daily temperature difference (degrees C), relative humidity (%), ambient atmospheric pressure (hPa), pressure, SO2 (ppm), NO2 (ppm), O-3 (ppm), CO (ppm), and PM10 (mu g/m(3)) of a mean of 60 days, 30 days, 14 days, 7 days, and 3 days before SSNHL were analyzed. Hourly measurements were taken from 94 places to assess the temperature, humidity, and atmospheric pressure and from 273 places to determine SO2, NO2, O-3, CO, and PM10. Crude and adjusted odds ratios (ORs) and 95% confidence intervals (CIs) of meteorological data for SSNHL were analyzed using unconditional logistic regression analyses. Subgroup analyses were conducted by age and sex. The mean NO2 and O-3 concentrations 14 days before the index date were different in the SSNHL group compared to those in the control group (P.< 0.001 for NO2 and P = 0.021 for O-3). The adjusted 14-day OR for NO2 (0.1 ppm) exposure was 3.12 in the SSNHL group compared to that in the control group (95% CI = 2.16-4.49, P < 0.001). The increased odds of NO2 exposure for 14 days in the SSNHL group persisted in the age group older than 30 years for both sexes. Other meteorological conditions did not show differences between the SSNHL and control groups. SSNHL was associated with high concentrations of NO2.