Background: Kawasaki disease exhibits a distinct seasonality, and short-term changes in weather may affect its occurrence.
Methods: To investigate the effects of weather variability on the occurrence of this syndrome, we conducted a time-between-events analysis of consecutive admissions for Kawasaki disease to a large pediatric hospital in Chicago. We used gamma regression to model the times between admissions. This is a novel application of gamma regression to model the time between admissions as a function of subject-specific covariates.
Results: We recorded 723 admissions in the 18-year (1986–2003) study period, of which 700 had complete data for analysis. Admissions for Kawasaki disease in Chicago were seasonal: The mean time between admissions was 34% shorter (relative time = 0.66, 95% confidence interval 0.54–0.81) from January–March than from July–September. In 1998, we recorded a larger number of admissions for Kawasaki disease (n = 65) than in other years (mean n = 37). January–March months of 1998 were warmer by a mean of 3°C (1.5°C–4.4°C) and the mean time between admissions was 48% shorter (relative time = 0.52, 0.36–0.75) than in equivalent periods of other study years.
Conclusions: Our findings show that atypical changes in weather affect the occurrence of Kawasaki disease and are compatible with a link to an infectious trigger. The analysis of interevent times using gamma regression is an alternative to Poisson regression in modeling a time series of sparse daily counts.
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From the aDivision of Pulmonary and Critical Care, Department of Medicine, The Johns Hopkins University, Baltimore, MD; bDivision of Infectious Diseases, Department of Pediatrics, Oregon Health and Science University, Portland, OR; cSchool of Engineering, Universidad Adolfo Ibañez, Santiago, Chile; dThe Center for Kawasaki Disease, Department of Pediatrics, The Children's Memorial Hospital, Feinberg School of Medicine, Northwestern University, Chicago, IL; and eNelson Institute for Environmental Studies and Department of Population Sciences, University of Wisconsin-Madison, Madison, WI.
Submitted 24 September 2007; accepted 13 August 2008; posted 5 January 2009.
Supported in part by the Kawasaki Disease Fund at Children's Memorial Hospital and a National Oceanic and Atmospheric Administration grant (Joint Program on Climate Variability and Human Health, with Electric Power Research Institute, National Science Foundation, Environmental Protection Agency, and National Aeronautics and Space Administration).
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Editors’ Note: A commentary on this article appears on page 202.
Correspondence: William Checkley, Division of Pulmonary and Critical Care, Department of Medicine, The Johns Hopkins School of Medicine, 1830 Monument St, 5th Floor, Baltimore, MD 21205. E-mail: email@example.com.