Geographic distribution of autism in California: A retrospective birth cohort analysis

Abstract

Prenatal environmental exposures are among the risk factors being explored for associations with autism. We applied a new procedure combining multiple scan cluster detection tests to identify geographically defined areas of increased autism incidence. This procedure can serve as a first hypothesis-generating step aimed at localized environmental exposures, but would not be useful for assessing widely distributed exposures, such as household products, nor for exposures from non-point sources, such as traffic. Geocoded mothers' residences on 2,453,717 California birth records, 1996–2000, were analyzed including 9,900 autism cases recorded in the California Department of Developmental Services (DDS) database through February 2006 which were matched to their corresponding birth records. We analyzed each of the 21 DDS Regional Center (RC) catchment areas separately because of wide variation in diagnostic practices. Ten clusters of increased autism risk were identified in eight RC regions, and one potential cluster in each of two other RC regions. After determination of clusters, multiple mixed Poisson regression models were fit to assess differences in known demographic autism risk factors between births within and outside areas of elevated autism incidence, independent of case status. Adjusted for other covariates, the majority of areas of autism clustering were characterized by high parental education, e.g., relative risks >4 for collegegraduate versus non-high school graduate parents. This geographic association possibly occurs because RCs do not actively conduct case finding and parents with lower education are, for various reasons, less likely to successfully seek services.

Scientists and autism: When geeks meet

“…A 2010 analysis of autism diagnoses in California 11 did not find that autism clustered preferentially around areas rich in IT industry. Instead, it found that clusters tended to occur in areas where parents were older and educated to a higher level than were parents in surrounding areas.…”

Environmental factors associated with autism spectrum disorder: a scoping review for the years 2003–2013

“…The importance of SES emerged as a predictor of ASD risk in nine studies, 102,119,172,[240][241][242][243][244][245] but findings were mixed. Mainly in American studies, a higher SES, using proxies such as maternal income, occupation and education, was associated with ASD.…”

“…102,244 Furthermore, spatial analysis of autism incidence in regions of California indicated a higher incidence that was independently characterized by higher levels of parental education. 245 …”

Facteurs environnementaux associés au trouble du spectre de l’autisme : étude de délimitation portant sur les années 2003 à 2013

“…Neuf études 102,119,172,[240][241][242][243][244][245] ont dégagé l'importance de la SSE comme prédicteur du risque de TSA, mais les constatations ont été mitigées. Des études, surtout améri-caines 172,[240][241][242] , ont établi un lien entre une meilleure SSE, mesurée par des substituts comme le revenu de la mère, sa profession et ses études, et le TSA.…”

“…ex., sous-diagnostic du TSA dans les familles dont la SSE est moins bonne) 102,244 . De plus, une analyse spatiale de l'incidence de l'autisme dans des régions de la Californie a révélé une incidence plus élevée, corrélée de manière indépendante aux études plus poussées faites par les parents 245 . .…”