3.0 Results

3.1 Description

There were 1649 deaths during the EHE (25 June – July 02, 2021) and 6700 deaths during the typical weather period (25 June – July 02, 2012-2020). We included 1614 EHE deaths and 6524 typical weather deaths after omitting 67 children (8 EHE; 59 typical weather), 95 deaths with missing location data (12 EHE; 83 typical weather), and 49 deaths with missing demographic information (15 EHE; 34 typical weather). During the EHE, there were 280 heat-related deaths (X30), 382 deaths with information still pending from BCCS (R99), and 952 non-heat-related deaths (not X30 or R99, Figure 3). More detailed information on cause of death for the entire study population is available in the supplementary materials (Figure S1). The mean annual number (range) of typical weather deaths was 725 (618-824). One typical weather death had extreme heat (X30) as the underlying cause, and 129 (2-50 per year) had an unknown or pending (R99) cause of death.
Overall, the age and sex distributions of the EHE and typical weather deaths were similar. The EHE group had higher proportions of decedents with schizophrenia, chronic kidney disease, diabetes, and depression than the typical weather group, as well as a higher total number of chronic diseases. The EHE group also had lower proportions of decedents with angina, dementia, and osteoporosis. Within the EHE group, there were some clear differences between the heat-related (X30), pending (R99), and non-heat-related (not X30 or R99) subgroups (Table 1).
We included 21 of the 26 chronic disease registries in conditional logistic regression. Juvenile arthritis was excluded because no children were included in this study (juvenile arthritis diagnoses require patients to be ≤ 15 years old). We removed multiple sclerosis and hemorrhagic stroke because <1% of EHE decedents had these conditions. Hospitalized stroke and mood/anxiety disorders were collinear with ischemic stroke and depression, respectively. All cases of ischemic stroke (N = 481) were also categorized as hospitalized stroke (N = 539), and all cases of depression (N = 3557) were also categorized as mood/anxiety disorder (N = 4124). In both cases, we excluded the higher-level category (i.e., hospitalized stroke, mood/anxiety disorder) because the lower-level category (i.e., ischemic stroke, depression) represented a more specific condition.
Table 1. Descriptive statistics. Demographics and chronic diseases among the extreme heat event (EHE) deaths and the typical weather comparison group. The EHE deaths are further subdivided into heat-related (ICD-10 code X30), pending (ICD-10 code R99), and non-heat-related subgroups (ICD-10 code not X30 or R99).