Emergency department visits, ambulance calls, and mortality associated with an exceptional heat wave in Sydney, Australia, 2011: a time-series analysis

Andrea Schaffer,Stephen Corbett,Wayne Smith,David Muscatello,Richard Broome

doi:10.1186/1476-069x-11-3

Abstract

BackgroundFrom January 30-February 6, 2011, New South Wales was affected by an exceptional heat wave, which broke numerous records. Near real-time Emergency Department (ED) and ambulance surveillance allowed rapid detection of an increase in the number of heat-related ED visits and ambulance calls during this period. The purpose of this study was to quantify the excess heat-related and all-cause ED visits and ambulance calls, and excess all-cause mortality, associated with the heat wave.MethodsED and ambulance data were obtained from surveillance and administrative databases, while mortality data were obtained from the state death registry. The observed counts were compared with the average counts from the same period from 2006/07 through 2009/10, and a Poisson regression model was constructed to calculate the number of excess ED visits, ambulance and deaths after adjusting for calendar and lag effects.ResultsDuring the heat wave there were 104 and 236 ED visits for heat effects and dehydration respectively, and 116 ambulance calls for heat exposure. From the regression model, all-cause ED visits increased by 2% (95% CI 1.01-1.03), all-cause ambulance calls increased by 14% (95% CI 1.11-1.16), and all-cause mortality increased by 13% (95% CI 1.06-1.22). Those aged 75 years and older had the highest excess rates of all outcomes.ConclusionsThe 2011 heat wave resulted in an increase in the number of ED visits and ambulance calls, especially in older persons, as well as an increase in all-cause mortality. Rapid surveillance systems provide markers of heat wave impacts that have fatal outcomes.

Highlights

From January 30-February 6, 2011, New South Wales was affected by an exceptional heat wave, which broke numerous records
During the 8-day heat wave, there were 104 Emergency Department (ED) visits for heat effects and 236 ED visits for dehydration, and 116 ambulance calls for heat exposure (Table 1)
The greatest daily counts for ED visits and ambulance calls for heat effects were observed on the hottest day of the heat wave (February 5), with 33 visits and 32 calls respectively

Summary

Introduction

From January 30-February 6, 2011, New South Wales was affected by an exceptional heat wave, which broke numerous records. During an extreme heat wave in France in 2003, maximum daily temperatures exceeded 35°C for 15 days; the number of excess deaths across the country due to the heat wave was estimated to be 14,800, equivalent to a 60% increase over the expected count [1]. In Paris alone, there were 2228 excess deaths with a 5-fold increased risk of death observed on the hottest day of the heat wave [2]. In Chicago in 1995 there was a 5-day heat wave which peaked on July 13 with a maximum temperature of 40°C [3]. The effect of the heat wave was delayed, with the greatest daily increase in mortality recorded two days after the hottest heat wave day, with an excess of 275 deaths [4]. Smaller increases in mortality during less severe heat waves have been observed in Europe [5,6,7,8,9], China [10], and the United States [11,12]

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