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Michael Waldman, PhD; Sean Nicholson, PhD; Nodir Adilov, PhD; John Williams, MD, MBA

Arch Pediatr Adolesc Med. 2008;162(11):1026-1034.

Objective  To investigate empirically the possibility of an environmental trigger for autism among genetically vulnerable children that is positively associated with precipitation.

Design  We used regression analysis to investigate autism prevalence rates and counts first in relation to mean annual county-level precipitation and then to the amount of precipitation a birth cohort was exposed to when younger than 3 years, controlling for time trend, population size, per capita income, and demographic characteristics. In some models, we included county fixed-effects rather than a full set of covariates.

Setting  Counties in California, Oregon, and Washington.

Participants  Children born in California, Oregon, and Washington between 1987 and 1999.

Main Exposure  County-level precipitation.

Main Outcome Measures  County-level autism prevalence rates and counts.

Results  County-level autism prevalence rates and counts among school-aged children were positively associated with a county's mean annual precipitation. Also, the amount of precipitation a birth cohort was exposed to when younger than 3 years was positively associated with subsequent autism prevalence rates and counts in Oregon counties and California counties with a regional developmental services center.

Conclusions  These results are consistent with the existence of an environmental trigger for autism among genetically vulnerable children that is positively associated with precipitation. Further studies focused on establishing whether such a trigger exists and identifying the specific trigger are warranted.

Author Affiliations: Johnson Graduate School of Management (Dr Waldman) and Department of Policy Analysis and Management (Dr Nicholson), Cornell University, Ithaca, New York; Department of Economics, Indiana University–Purdue University, Fort Wayne (Dr Adilov); and Department of Child and Adolescent Psychiatry, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania (Dr Williams).

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RELATED LETTERS

Autism Prevalence and Precipitation: The Potential for Cross-Level Bias
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Arch Pediatr Adolesc Med. 2009;163(5):492.
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