Heat-related Emergency Hospitalizations for Respiratory Diseases in the Medicare Population

Abstract

Rationale: The heat-related risk of hospitalization for respiratory diseases among the elderly has not been quantified in the United States on a national scale. With climate change predictions of more frequent and more intense heat waves, it is of paramount importance to quantify the health risks related to heat, especially for the most vulnerable. Objectives: To estimate the risk of hospitalization for respiratory diseases associated with outdoor heat in the U.S. elderly. Methods: An observational study of approximately 12.5 million Medicare beneficiaries in 213 United States counties, January 1, 1999 to December 31, 2008. We estimate a national average relative risk of hospitalization for each 10 8 F (5.6 8 C) increase in daily outdoor temperature using Bayesian hierarchical models. Measurements and Main Results: We obtained daily county-level rates of Medicare emergency respiratory hospitalizations (International Classification of Diseases, Ninth Revision,(464)(465)(466)(480)(481)(482)(483)(484)(485)(486)(487)(490)(491)(492) in 213 U.S. counties from 1999 through 2008. Overall, each 10 8 F increase in daily temperature was associated with a 4.3% increase in same-day emergency hospitalizations for respiratory diseases (95% posterior interval, 3.8, 4.8%). Counties' relative risks were significantly higher in counties with cooler average summer temperatures. Conclusions: We found strong evidence of an association between outdoor heat and respiratory hospitalizations in the largest population of elderly studied to date. Given projections of increasing temperatures from climate change and the increasing global prevalence of chronic pulmonary disease, the relationship between heat and respiratory morbidity is a growing concern.Keywords: chronic obstructive pulmonary disease; hospitalization; hot temperature; respiratory tract infections; weatherOutdoor heat can cause spikes in respiratory deaths (1, 2), but considerably less is known about heat's impacts on respiratory morbidity. Given that: (1) climate change will increase exposure to extreme heat (3), (2) the prevalence of chronic respiratory diseases is increasing (4), and (3) the elderly will likely be most affected by heat-related problems (5), there is a pressing need to improve our understanding of respiratory heat effects among the elderly for both fatal and nonfatal outcomes.There are two major limitations to current research on the relationship between heat and respiratory hospitalizations. First, this relationship has not been adequately studied worldwide to confidently identify a consistent link between respiratory hospitalizations and heat. The few studies that have investigated heat and respiratory hospitalizations have found somewhat conflicting results (6). For example, studies of Brisbane, Australia (7,8) and Athens, Greece (9) found hospitalization rates decreased slightly during hot weather, whereas studies of California (10, 11), New York (12, 13), and 12 European cities (14) found respiratory hospitalizations increased with heat. Although a me...

Effect of Missing Data on Estimation of the Impact of Heat Waves: Methodological Concerns for Public Health Practice

“…Time-series analyses are also used to investigate associations between morbidity and periods of extreme heat [1,12]. Further, in Lu and Zeger [19], they demonstrate that when the exposure is common to the cohort at the time (as it is here), that case-crossover approach is equivalent to a log-linear time series analysis.…”

“…The Breslow method [20] was used to minimize any potential exposure bias due to ties [21] and cubic B-splines, with 3 equally spaced knots, for fixed effects of time are considered. Because of published reports of a lag effect of temperature [1,3,5,12], lagged-day heat index exposures for block-kriged county daily heat index of same day (no lag), 1-day lag, 2-day lag, and 3-day lag are considered in the analyses.…”

“…Further, these missing data can change analytical and public health conclusions from these studies. Previously, public health researchers have either focused on times of known extreme heat events, eliminating the need for a data-driven extreme heat definition; studied one locale or city-specific heat waves, which typically results in exposure data having similar quality or patterns of missingness across heat waves; or have used only 10-20 years of weather data to define extreme heat, a shorter duration than that used in climate science [1][2][3][4][5][6].…”

“…In a later paper, Tong et al [12], conducted both time-series and case-crossover analyses to assess short-term association between heat waves and both morbidity and mortality. To estimate the risk of hospitalization for respiratory diseases associated with outdoor heat, Anderson et al [1] used a time-series model with the county-level daily hospitalization rate during May to September, from [1999][2000][2001][2002][2003][2004][2005][2006][2007][2008]. Modeling the daily number of heat-related emergency department visits during 2007 and 2008, by age group, county and day, a time-series model was also used to estimate the association between average daily mean temperature and heat-related emergency department visits in Lippman et al [4].…”

“…These studies generally exclude cases described as having external causes of injury [10], i.e., car accident; however, associations may be difficult to interpret. Other studies use specific groupings of International Classification of Disease (ICD) codes or specific symptoms to focus their studies on illnesses of interest such as exertional heat-related illness, diabetes, cardiovascular diseases, pulmonary diseases, kidney illnesses, and preterm delivery [1][2][3]5,6,11]. These more focused studies typically have motivating biological mechanisms or processes to inform interpretations.…”