Urbanization may affect the incidence of urolithiasis in South Korea

BACKGROUND We evaluated the different climatic factors in urban and rural areas that may affect the incidence of urolithiasis. Nationwide data on urolithiasis were acquired from Health Insurance Review and Assessment Service between 2009 and 2013. Information on age, gender, date of diagnosis, geographic region and daily weather data from all weather stations was collected. The data were grouped by population density and substituted into the lag period model. The primary outcome was the incidence rate in each region. The secondary outcomes were differences between groups and relative risks (RRs) of climatic factors. The tertiary outcome was RRs of urolithiasis presentation cumulated over a 20-day lag period associated with the mean daily temperature. RESULTS The incidence rates of urolithiasis tended to increase annually in most regions from 2009 to 2013. The urban group showed a higher mean temperature, lower amount of rainfall, higher wind speed and lower mean relative humidity than the rural group (p < 0.001). The urban group showed significant RRs of temperature (1.013, 95% confidence interval [CI] 1.009-1.017, p < 0.001), wind speed (0.979, CI 0.973-0.986, p < 0.001), humidity (0.995, CI 0.994-0.996, p < 0.001), and sunshine (0.992, CI 0.988-0.996, p < 0.001). The rural group showed significant RRs of wind speed (0.980, CI 0.968-0.992, p = 0.002) and humidity (0.998, CI 0.996-0.999, p = 0.007). In the urban area, RRs increased gradually with increasing temperature. CONCLUSIONS Regional differences in climatic factors, especially temperature, may provoke a gap in urolithiasis events between the urban and rural areas.