Average Temperature, Diurnal Temperature Variation, and Stroke Hospitalizations

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Background

Studies assessing the relationship between meteorological factors and stroke incidence are inconsistent. We assessed the associations of average temperature and diurnal temperature fluctuations with ischemic stroke hospitalizations in a nationally representative sample of patients in the United States.

Methods

Hospitalizations were identified for adults aged 18 years or older in the 2009-2011 Nationwide Inpatient Sample and linked with county-level monthly average temperatures from the United States National Climatic Data Center. Logistic regression models assessed the relationships of 5°F increases in average temperature and diurnal temperature variation (difference between high- and low-daily temperatures) with the odds of ischemic stroke hospitalization (International Classification of Diseases, Ninth Revision, Clinical Modification codes 433, 434, and 436), adjusting for patient characteristics and dew point. Models were stratified by age (18-64, ≥65 years), season, and region, with analysis at the hospitalization level.

Results

Increased average temperature was associated with decreased odds of stroke hospitalization among both age groups and across seasons in the Northeast, and among the elderly in the West. Increased diurnal temperature variation was associated with increased odds of stroke hospitalization for nearly all regions in the spring to fall seasons; associations were most pronounced in the Northeast and strongest in the spring.

Conclusions

Lower average temperature and larger diurnal temperature variations were associated with stroke hospitalizations. Associations were strongest in the Northeast and largely similar across seasons and age. Further research is needed to explore the mechanisms underlying these associations. Understanding these patterns may lead to targeted prevention strategies for vulnerable populations during periods of extreme weather conditions.

Introduction

Stroke represents a significant public health burden in the United States, with approximately 795,000 events occurring each year.1 Stroke is the country's fifth leading cause of death and a leading cause of long-term disability. Seasonal variation in stroke incidence has been reported in many populations and may be mediated through changes in temperature and barometric pressure.2 The majority of prior studies report higher stroke rates in colder months compared with other times of the year3, 4, 5, 6, 7, 8, 9; however, some studies report no seasonal patterns10 or higher rates in spring, summer, or autumn.11, 12, 13, 14

There are only limited U.S. data assessing the association between temperature and stroke risk, irrespective of seasonal effects and with adjustment for patient-level comorbidities. In a longitudinal study of mortality after ischemic stroke in the United States, we found a seasonal trend for higher mortality rates in colder months with a second peak in July.15 The current study expands this research by exploring the impact of meteorological factors, including average temperature and diurnal temperature variation, on stroke hospitalizations across geographic regions of the United States.

Section snippets

Methods

Hospital admissions for ischemic stroke (International Classification of Diseases, Ninth Revision, Clinical Modification codes 433.xx, 434.xx, and 436.xx)16 were identified among all hospitalizations for calendar years 2009-2011 in the Nationwide Inpatient Sample (NIS), a multistate database developed as part of the United States Agency for Healthcare Research and Quality's Healthcare Cost and Utilization Project.17 The NIS is the largest publicly available, all-payer, inpatient database in the

Results

The final cohort included 9,909,608 hospitalizations; 171,695 (1.7%) were ischemic stroke hospitalizations (Table 1). The mean age of the younger population (aged 18-64 years) was 54.4 years and for the older population (≥65 years) was 78.7 years; women represented approximately half of the hospitalizations. Stroke patients had a high prevalence of comorbid conditions, including heart failure, hypertension, and diabetes. Black race and diabetes were more common in younger than older stroke

Discussion

In this large, nationally representative sample of U.S. patients, we found that larger diurnal temperature fluctuations were associated with higher stroke hospitalization rates, even after adjusting for patient demographic characteristics and comorbid conditions. This association was evident for nearly all regions and seasons, but it was most notable in the Northeast. Increased average temperature was associated with lower stroke hospitalization rates; however, this relationship was largely

Conclusions

We found that larger daily fluctuations in temperature were associated with increased odds of stroke hospitalization for most of the United States, whereas higher average temperatures were associated with decreased hospitalizations primarily in the Northeast. Further characterization and understanding of meteorological effects on stroke risk could lead to targeted prevention efforts in vulnerable populations such as the very elderly living in regions with extreme temperature fluctuations.

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