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American Journal of Epidemiology Advance Access originally published online on January 22, 2009
American Journal of Epidemiology 2009 169(5):588-595; doi:10.1093/aje/kwn383
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American Journal of Epidemiology © 2009 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

ORIGINAL CONTRIBUTIONS

Environmental Exposures and Invasive Meningococcal Disease: An Evaluation of Effects on Varying Time Scales

Laura M. Kinlin, C. Victor Spain, Victoria Ng, Caroline C. Johnson, Alexander N. J. White and David N. Fisman

Correspondence to Dr. David N. Fisman, Research Institute of the Hospital for Sick Children, 123 Edward Street, Room 428, Toronto, Ontario, Canada M5G 1E2 (e-mail: david.fisman{at}gmail.com).

Received for publication February 15, 2008. Accepted for publication November 5, 2008.

Invasive meningococcal disease (IMD) is an important cause of meningitis and bacteremia worldwide. Seasonal variation in IMD incidence has long been recognized, but mechanisms responsible for this phenomenon remain poorly understood. The authors sought to evaluate the effect of environmental factors on IMD risk in Philadelphia, Pennsylvania, a major urban center. Associations between monthly weather patterns and IMD incidence were evaluated using multivariable Poisson regression models controlling for seasonal oscillation. Short-term weather effects were identified using a case-crossover approach. Both study designs control for seasonal factors that might otherwise confound the relation between environment and IMD. Incidence displayed significant wintertime seasonality (for oscillation, P < 0.001), and Poisson regression identified elevated monthly risk with increasing relative humidity (per 1% increase, incidence rate ratio = 1.04, 95% confidence interval: 1.004, 1.08). Case-crossover methods identified an inverse relation between ultraviolet B radiation index 1–4 days prior to onset and disease risk (odds ratio = 0.54, 95% confidence interval: 0.34, 0.85). Extended periods of high humidity and acute changes in ambient ultraviolet B radiation predict IMD occurrence in Philadelphia. The latter effect may be due to decreased pathogen survival or virulence and may explain the wintertime seasonality of IMD in temperate regions of North America.

case-control studies; environment; environmental exposure; meningitis; meningitis, bacterial; meteorological factors; Neisseria meningitidis; regression analysis

Abbreviations: CI, confidence interval; IRR, incidence rate ratio; OR, odds ratio; UVB, ultraviolet B


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