Mixed-methods evaluation and enhancement of Peel Public Health's heat-related illness emergency department visit surveillance system, 2018-2024.

BACKGROUND

Climate change contributes to increased heat events, which are associated with negative health outcomes. Peel Public Health, a health unit in Ontario, has conducted emergency department (ED) visit surveillance during heat events since 2018 using Acute Care Enhanced Surveillance data.

OBJECTIVE

To optimize local public health surveillance of heat-related illnesses, a mixed-methods evaluation of system usefulness and representativeness was conducted and the system was enhanced through retrospective observational analyses.

METHODS

The surveillance usefulness was evaluated through semi-structured interviews with ten recipients of the surveillance product and representativeness by determining the impact of data by patient address compared to hospital address over 2018-2024. Retrospective analyses of 2018-2024 data identified associations between heat events and surveillance ED indicators. Findings informed surveillance revisions.

RESULTS

Interviewees interpreted the original surveillance product as a high-level real-time snapshot of downstream health outcomes, useful for situational awareness and understanding of whether ED visits were increasing. Recommendations included adding key messages, thresholds/ranges and subgroup information. Representativeness evaluation showed that 27.2% of ED visits by Peel residents were at non-Peel hospitals and 14.0% of Peel hospital ED visits were by non-Peel residents. Daily counts of heat-related illnesses were significantly associated with heat event days (incidence rate ratio: 6.43, 95% confidence interval: 3.86-10.71).

CONCLUSION

A revised surveillance product was implemented for 2025 including standard deviations, aberration alerts adapted from preexisting criteria, ED visits based on hospital address and stratification by three subgroups (aged older than 65 years and younger than five years, and elevated heat vulnerability) to increase usefulness for situational awareness.