The Effects of Extreme Heat on Mental Disorder Admissions in Hlabisa, South Africa: A 13-Year Time-Series Analysis

Background: Extreme heat is increasingly linked to adverse mental health outcomes, yet empirical evidence from sub-Saharan Africa is absent. Such data are critical for health system planning and climate adaptation in one of the world's most heat-vulnerable regions. Objectives: We aimed to estimate the immediate and delayed effects of daily maximum temperature on mental disorder-related hospital admissions in a rural South African district over 13 years. Methods: We conducted a time-series analysis of daily mental disorder admissions at Hlabisa Hospital, South Africa, from 2011 to 2023. Daily maximum temperatures were obtained from ECMWF ERA5 reanalysis and validated with local weather station data. Using distributed lag non-linear quasi-Poisson models, we estimated the association between extreme heat (95th, 97.5th, 99th percentiles of the daily maximum temperature distribution) and relative risk of mental disorder admissions over a 0-21-day lag. Analyses were stratified by sex, age (<60 vs. & >=60 years), and diagnosis (schizophrenia vs. other mental disorders). Results: Between 2011 and 2023, 1760 mental disorder admissions were recorded. Extreme heat at the 97.5th percentile (35.74 degrees celsius) was associated with an immediate increase in admissions (lag 0: RR=1.10, 95 % CI: 1.00 to 1.20; lag 1: RR=1.08, 95% CI: 1.00 to 1.17). Subgroup analyses revealed heterogeneous patterns, with early increases among females and individuals with diagnoses other than schizophrenia, delayed increases among males and those aged <60 years, and delayed decreases among females and older adults. No significant association was observed for schizophrenia. Discussion: To our knowledge, this study provides the first empirical evidence from South Africa that extreme heat is associated with increased hospital admissions for mental disorders, with immediate and delayed effects across population subgroups. These findings highlight the need to integrate mental health into climate adaptation and public health strategies through strengthened surveillance, targeted protection of vulnerable groups, and enhanced health system preparedness for extreme heat.