Forty-year Seasonality Trends in Occurrence of Myocardial Infarction, Ischemic Stroke, and Hemorrhagic Stroke

Nils Skajaa, E. Puhó, Jens Sundbøll, Kasper Adelborg, Kenneth J. Rothman, Henrik Toft Sørensen

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Abstract

BACKGROUND: The occurrence of myocardial infarction (MI), ischemic stroke, and hemorrhagic stroke has decreased in recent years, but trends in seasonal occurrence remain unclear. METHODS: Using Danish healthcare databases, we identified all patients with a first-time MI, ischemic stroke, or hemorrhagic stroke during the study period (1977-2016). We summarized monthly cases for each disease separately and computed the peak-to-trough ratio as a measure of seasonal occurrence of one cycle. To examine trends over time in seasonal occurrence, we computed the peak-to-trough ratio for each of the 40 years. We also quantified the amount of bias arising from random error in peak-to-trough ratios. RESULTS: Before consideration of bias, the peak-to-trough ratio of summarized monthly cases was 1.11 (95% confidence interval [CI] = 1.10, 1.12) for MI, 1.08 (95% CI = 1.07, 1.09) for ischemic stroke, and 1.12 (95% CI = 1.10, 1.14) for hemorrhagic stroke. The peak-to-trough ratio of MI occurrence increased from 1.09 (95% CI = 1.04, 1.15) in 1977 to 1.16 (95% CI = 1.09, 1.23) in 1999. The trend then remained stable. The peak-to-trough ratio of ischemic stroke occurrence declined continuously during the study period, dropping from 1.12 (95% CI = 1.02, 1.24) in 1977 to 1.06 (95% CI = 1.00, 1.12) in 2016. The peak-to-trough ratio of hemorrhagic stroke occurrence remained stable over time. However, after adjusting for potential bias, time trends in peak-to-trough ratios were almost flat. CONCLUSIONS: We found no substantial seasonality for MI, ischemic stroke, or hemorrhagic stroke occurrence during 1977-2016. Modest peak-to-trough ratios should be interpreted after considering bias induced by random variation.

Original languageEnglish
Pages (from-to)777-783
Number of pages7
JournalEpidemiology (Cambridge, Mass.)
Volume29
Issue number6
DOIs
Publication statusPublished - Nov 1 2018

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Stroke
Myocardial Infarction
Confidence Intervals
Databases
Delivery of Health Care

ASJC Scopus subject areas

  • Epidemiology

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Forty-year Seasonality Trends in Occurrence of Myocardial Infarction, Ischemic Stroke, and Hemorrhagic Stroke. / Skajaa, Nils; Puhó, E.; Sundbøll, Jens; Adelborg, Kasper; Rothman, Kenneth J.; Sørensen, Henrik Toft.

In: Epidemiology (Cambridge, Mass.), Vol. 29, No. 6, 01.11.2018, p. 777-783.

Research output: Contribution to journalArticle

Skajaa, Nils ; Puhó, E. ; Sundbøll, Jens ; Adelborg, Kasper ; Rothman, Kenneth J. ; Sørensen, Henrik Toft. / Forty-year Seasonality Trends in Occurrence of Myocardial Infarction, Ischemic Stroke, and Hemorrhagic Stroke. In: Epidemiology (Cambridge, Mass.). 2018 ; Vol. 29, No. 6. pp. 777-783.
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AU - Skajaa, Nils

AU - Puhó, E.

AU - Sundbøll, Jens

AU - Adelborg, Kasper

AU - Rothman, Kenneth J.

AU - Sørensen, Henrik Toft

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N2 - BACKGROUND: The occurrence of myocardial infarction (MI), ischemic stroke, and hemorrhagic stroke has decreased in recent years, but trends in seasonal occurrence remain unclear. METHODS: Using Danish healthcare databases, we identified all patients with a first-time MI, ischemic stroke, or hemorrhagic stroke during the study period (1977-2016). We summarized monthly cases for each disease separately and computed the peak-to-trough ratio as a measure of seasonal occurrence of one cycle. To examine trends over time in seasonal occurrence, we computed the peak-to-trough ratio for each of the 40 years. We also quantified the amount of bias arising from random error in peak-to-trough ratios. RESULTS: Before consideration of bias, the peak-to-trough ratio of summarized monthly cases was 1.11 (95% confidence interval [CI] = 1.10, 1.12) for MI, 1.08 (95% CI = 1.07, 1.09) for ischemic stroke, and 1.12 (95% CI = 1.10, 1.14) for hemorrhagic stroke. The peak-to-trough ratio of MI occurrence increased from 1.09 (95% CI = 1.04, 1.15) in 1977 to 1.16 (95% CI = 1.09, 1.23) in 1999. The trend then remained stable. The peak-to-trough ratio of ischemic stroke occurrence declined continuously during the study period, dropping from 1.12 (95% CI = 1.02, 1.24) in 1977 to 1.06 (95% CI = 1.00, 1.12) in 2016. The peak-to-trough ratio of hemorrhagic stroke occurrence remained stable over time. However, after adjusting for potential bias, time trends in peak-to-trough ratios were almost flat. CONCLUSIONS: We found no substantial seasonality for MI, ischemic stroke, or hemorrhagic stroke occurrence during 1977-2016. Modest peak-to-trough ratios should be interpreted after considering bias induced by random variation.

AB - BACKGROUND: The occurrence of myocardial infarction (MI), ischemic stroke, and hemorrhagic stroke has decreased in recent years, but trends in seasonal occurrence remain unclear. METHODS: Using Danish healthcare databases, we identified all patients with a first-time MI, ischemic stroke, or hemorrhagic stroke during the study period (1977-2016). We summarized monthly cases for each disease separately and computed the peak-to-trough ratio as a measure of seasonal occurrence of one cycle. To examine trends over time in seasonal occurrence, we computed the peak-to-trough ratio for each of the 40 years. We also quantified the amount of bias arising from random error in peak-to-trough ratios. RESULTS: Before consideration of bias, the peak-to-trough ratio of summarized monthly cases was 1.11 (95% confidence interval [CI] = 1.10, 1.12) for MI, 1.08 (95% CI = 1.07, 1.09) for ischemic stroke, and 1.12 (95% CI = 1.10, 1.14) for hemorrhagic stroke. The peak-to-trough ratio of MI occurrence increased from 1.09 (95% CI = 1.04, 1.15) in 1977 to 1.16 (95% CI = 1.09, 1.23) in 1999. The trend then remained stable. The peak-to-trough ratio of ischemic stroke occurrence declined continuously during the study period, dropping from 1.12 (95% CI = 1.02, 1.24) in 1977 to 1.06 (95% CI = 1.00, 1.12) in 2016. The peak-to-trough ratio of hemorrhagic stroke occurrence remained stable over time. However, after adjusting for potential bias, time trends in peak-to-trough ratios were almost flat. CONCLUSIONS: We found no substantial seasonality for MI, ischemic stroke, or hemorrhagic stroke occurrence during 1977-2016. Modest peak-to-trough ratios should be interpreted after considering bias induced by random variation.

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