Heat and hospital admission via the emergency department for people with intellectual disability, autism, and mental disorders in South Korea: a nationwide, time-stratified, case-crossover study

Background Given the anticipated increase in ambient temperature due to climate change, the hazardous effects of heat on health have been extensively studied; however, its impact on people with intellectual disability, autism, and mental illness is largely unknown. We aimed to estimate the association between heat and hospitalisation through the emergency department (ED) among people with these mental disorders. Methods In this nationwide study, we used data from the National Health Insurance Database (NHID) of the National Health Insurance Service, the single universal insurer in South Korea, the claims data for which is based on the ICD-10. We included individuals with identified intellectual disability, autism, and mental disorders (including schizophrenia, bipolar disorder, recurrent depressive disorder, schizoaffective disorder and persistent obsessive-compulsive disorder, Tourette's disorder, and narcolepsy) and we established two control groups of people without these disorders: one including 1 million systematically sampled individuals, and one matched to the cohort based on sex, age, and income group. Data on hospital admission via the ED were obtained from the NHID, including the primary cause of admission and corresponding medical costs, for the warm season (June–September) of the period 2006–2021. We used the Google Earth Engine with the ERA5-Land dataset to collect data on the daily mean temperature. We applied a time-stratified case-crossover design using a distributed lag non-linear model and performed a conditional logistic regression. The risk ratio was estimated as the odds ratio (OR) with calculated odds at the 99th percentile temperature compared with that at the local 75th percentile temperature. We did not include people with lived experience of mental illness in this study. Findings Of the 456 946 people with intellectual disability, autism, or mental disorder in the NHID records, 99 845 were admitted to the ED, including 59 821 (59·9%) males and 40 024 (40·1%) females, and including 29 192 people with intellectual disability, 1428 people with autism, and 69 225 people with mental disorders. We were not able to collect data on ethnicity. The mean age at ED admission was 42·1 years (SD 17·9, range 0–102) for people with intellectual disability, 18·6 years (SD 10·4, range 1–72) for people with autism, and 50·8 years (SD 11·9, range 2–94) for people with mental disorders. The heat OR (odds at the 99th percentile vs 75th percentile of temperature) of ED admission was 1·23 (95% CI 1·11–1·36) for intellectual disability, 1·06 (0·68–1·63) for autism, and 1·20 (1·12–1·29) for mental disorders. People with intellectual disability, female individuals, people living in rural areas, or those with a low-income status were at increased risk of ED admission due to heat. The risk of ED admission due to genitourinary diseases was higher than that from other causes. Annual increase in medical costs attributable to heat among people with intellectual disability, autism, and mental disorders was US$ 224 970 per 100 000 person-years (95% empirical CI 139 784–305 770). Interpretation People with intellectual disability, autism, and mental disorders should be included in groups considered at a high-risk for heat exposure, and heat adaptation policies should be implemented with consideration of these groups and their needs. Funding The National Research Foundation of Korea, Korean Ministry of Environment, and Korean Ministry of Education. Translation For the Korean translation of the abstract see Supplementary Materials section.