Association between heat and upper urinary tract stones morbidity and medical costs: A study in the subtropical humid climate zone

Urolithiasis is a heat-specific disease. Exploring heat-related urolithiasis susceptibility subtypes, economic burden, and modifying factors could assist governments in targeting interventions to reduce the heat-related health risks of urolithiasis morbidity. We collected data on 23,492 patients with upper urinary tract stones (main subtypes of urolithiasis) from 2013 to 2017 in Nanjing, China. We adopted generalized additive quasi-Poisson models to examine the associations between daily mean temperatures and morbidity of upper urinary tract stones, while generalized additive Gaussian models were used to explore the relationships between temperatures and log-transformed medical costs. We examined the modification effects of disease subtypes (kidney and ureteral calculus), sex, and age through stratified analyses and the modification effects of other meteorological factors by introducing interaction terms in the models. We found that short-term summer heat exposure has a statistically significant effect on ureteral calculus morbidity but not on kidney calculus morbidity. For ureter calculus, a 1 °C temperature increase was associated with a 4.36% (95% confidence interval [CI]: 1.94%, 6.83%) increase in daily hospitalization and a 5.44% (95% CI: 2.71%, 8.25%) increase in daily medical costs. The attributable fraction associated with heat (greater than the median value of daily mean temperature, 26.8 °C) was 7.85% (95% empirical confidence interval [eCI]: 3.64%, 11.44%) for hospitalization and 9.36% (95% eCI: 4.91%, 13.14%) for medical costs. The effects of heat on ureter calculus morbidity were significantly higher among the males and those with high sunshine duration than females and those with low sunshine duration. Short-term summer heat exposure was associated with increased morbidity and medical costs of ureteral calculus. Relevant government organizations should take effective intervention measures, including community health education, to reduce the health hazards and economic losses caused by heat.