Multimorbidity and emergency hospitalisations during hot weather

Background People with chronic diseases are a commonly listed heat -vulnerable group in heat -health action plans. While prior research identi fi es multiple health conditions that may increase vulnerability to ambient heat, there is minimal evidence regarding the implications of multimorbidity (two or more chronic diseases). Methods From the statewide hospital registry of Queensland, Australia, we identi fi ed people aged >= 15 years who had emergency hospitalisation(s) between March 2004 and April 2016 and previously had 0, 1, 2, or >= 3 of fi ve chronic diseases: cardiovascular disease, diabetes, mental disorders, asthma/COPD, and chronic kidney disease. We conducted time-strati fi ed case-crossover analyses to estimate the odds ratio of hospitalisations associated with ambient heat exposure in people with different numbers, types, and combinations of chronic diseases. Ambient heat exposure was de fi ned as a 5 degrees C increase in daily mean temperature above the median. Findings There were 2,263,427 emergency hospitalisations recorded (48.7% in males and 51.3% in females). When the mean temperature increased, hospitalisation odds increased with chronic disease number, particularly in older persons ( >= 65 years), males, and non-indigenous people. For instance, in older persons with 0, 1, 2, or >= 3 chronic diseases, the odds ratios associated with ambient heat exposure were 1.00 (95% con fi dence interval: 0.96, 1.04), 1.06 (1.02, 1.09), 1.08 (1.02, 1.14), and 1.13 (1.07, 1.19), respectively. Among the chronic diseases, chronic kidney disease, and asthma/COPD, either existing alone, together, or in combination with other diseases, were associated with the highest odds of hospitalisations under ambient heat exposure. Interpretation While individuals with multimorbidity are considered in heat -health action plans, this study suggests the need to consider speci fi cally examining them as a distinct and vulnerable subgroup.