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. 2008 Jul 30:7:42.
doi: 10.1186/1476-072X-7-42.

Demographic, seasonal, and spatial differences in acute myocardial infarction admissions to hospital in Melbourne Australia

Margaret E Loughnan  1 , Neville Nicholls, Nigel J Tapper
Affiliations

Demographic, seasonal, and spatial differences in acute myocardial infarction admissions to hospital in Melbourne Australia

Margaret E Loughnan et al. Int J Health Geogr. .

Abstract

Background: Seasonal patterns in cardiac disease in the northern hemisphere are well described in the literature. More recently age and gender differences in cardiac mortality and to a lesser extent morbidity have been presented. To date spatial differences between the seasonal patterns of cardiac disease has not been presented. Literature relating to seasonal patterns in cardiac disease in the southern hemisphere and in Australia in particular is scarce. The aim of this paper is to describe the seasonal, age, gender, and spatial patterns of cardiac disease in Melbourne Australia by using acute myocardial infarction admissions to hospital as a marker of cardiac disease.

Results: There were 33,165 Acute Myocardial Infarction (AMI) admissions over 2186 consecutive days. There is a seasonal pattern in AMI admissions with increased rates during the colder months. The peak month is July. The admissions rate is greater for males than for females, although this difference decreases with advancing age. The maximal AMI season for males extends from April to November. The difference between months of peak and minimum admissions was 33.7%. Increased female AMI admissions occur from May to November, with a variation between peak and minimum of 23.1%. Maps of seasonal AMI admissions demonstrate spatial differences. Analysis using Global and Local Moran's I showed increased spatial clustering during the warmer months. The Bivariate Moran's I statistic indicated a weaker relationship between AMI and age during the warmer months.

Conclusion: There are two distinct seasons with increased admissions during the colder part of the year. Males present a stronger seasonal pattern than females. There are spatial differences in AMI admissions throughout the year that cannot be explained by the age structure of the population. The seasonal difference in AMI admissions warrants further investigation. This includes detailing the prevalence of cardiac disease in the community and examining issues of social and environmental justice.

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Figures

Figure 1
Figure 1
Monthly AMI admissions ratio for each year 1999–2004.
Figure 2
Figure 2
Monthly percentage difference for AMI admissions rates between each calendar month and base month December and average monthly temperature.
Figure 3
Figure 3
Percentage difference between peak and base months showing the seasonal patterns in AMI admissions for males in each of the four age groups.
Figure 4
Figure 4
Percentage difference between peak and base months showing the seasonal patterns in AMI admissions for females in each of the four age groups.
Figure 5
Figure 5
Percentage difference between each calendar month and the base month December for male AMI admissions aged 35 years and older and 55 years and older.
Figure 6
Figure 6
Percentage difference in monthly AMI admissions for males and females aged 55 years and older 1999–2004.
Figure 7
Figure 7
AMI admissions during (a) maximal and (b) minimal AMI seasons in Melbourne during study period 1999–2004 (number of SLAs in parenthesis).
Figure 8
Figure 8
Univariate Moran's I (LISA) cluster maps for SIR of AMI admissions in (a) maximal and (b) minimal season.
Figure 9
Figure 9
Bivariate Moran's I (LISA) cluster maps for SIR of AMI admissions and age during the (a) maximal and (b) minimal seasons.
See this image and copyright information in PMC

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