Seasonal Variations in Hospital Admissions for ST-Elevation Myocardial Infarction in New Zealand

BACKGROUND: Increased numbers of ST Elevation Myocardial Infarction (STEMI) admissions have been observed during winter in many countries. Our aim was to assess if seasonal variation of STEMI was present in the Waikato region of New Zealand. METHODS: Case notes of patients admitted to Waikato hospital with STEMI between July 1998 and December 2007 were analysed. The incidence of STEMI during summer (December to February), autumn (March to May), winter (June to August) and spring (September to November) were calculated. The individuals were divided into 2 age groups of ≤ 70 and > 70 years of age. RESULTS: A total of 3,569 patients (mean age 66.9 ± 14.1 years, 64% men) were included. STEMI presentation during winter was significantly higher compared with summer (35 ± 13 versus 27.3 ± 11.3 cases per month, P < 0.02) with 3 additional STEMI admissions per fortnight during winter months. The increase in STEMI in winter was more apparent in patients > 70 years of age, with an 8.5% increase in winter admissions compared to summer (P < 0.01). There was no significant difference in the incidence of STEMI between other seasons. CONCLUSION: There is a higher incidence of STEMI during winter in the Waikato region compared with summer. This increased incidence is particularly pronounced in patients over 70 years of age. Further investigations are necessary to elicit potential causes.