Geographic distribution of autism in California: a retrospective birth cohort analysis:
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 nonpoint 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 the 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 the 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 college-graduate vs. nonhigh-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.
More from ScienceDaily:
However, the researchers said that in this investigation the clusters probably are not correlated with specific environmental pollutants or other “exposures.” Rather, they correlate to areas where residents are more educated.
“What we found with these clusters was that they correlated with neighborhoods of high education or neighborhoods that were near a major treatment center for autism,” said senior author Irva Hertz-Picciotto, a professor of public health sciences and a researcher with the UC Davis MIND Institute.“In the U.S., the children of older, white and highly educated parents are more likely to receive a diagnosis of autism or autism spectrum disorder. For this reason, the clusters we found are probably not a result of a common environmental exposure. Instead, the differences in education, age and ethnicity of parents comparing births in the cluster versus those outside the cluster were striking enough to explain the clusters of autism cases,” Hertz-Picciotto said.
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Van Meter said that the increased risk of autism in these areas is roughly a doubling of the incidence of autism over the incidence in the surrounding zone. For example, for the cluster area located in the service zone of the San Diego Regional Center, the autism incidence was 61.2 per 10,000 births and, in the rest of the Regional Center service zone, 27.1 per 10,000 births. For the Harbor Regional Center the incidence was 103.4 and 57.8, respectively. Van Meter added that it is important to remember that most of the children with autism were not born in the cluster areas.
In Southern California, the areas of increased incidence were located within these Regional Center service zones:
1. The Westside Regional Center, headquartered in Culver City, Calif., which serves the communities of western Los Angeles County, including the cities of Culver City, Inglewood and Santa Monica;
2. The Harbor Regional Center, headquartered in Torrance, Calif., which serves southern Los Angeles County, including the cities of Bellflower, Harbor, Long Beach and Torrance;
3. The North Los Angeles County Regional Center, headquartered in Van Nuys, Calif., which serves the San Fernando and Antelope valleys — two clusters were located in this regional center’s service zone.
4. The South Central Los Angeles Regional Center, headquartered in Los Angeles, which serves the communities of Compton and Gardena;
5. The Regional Center of Orange County, headquartered in Santa Ana, Calif., which serves the residents of Orange County; and
6. The Regional Center of San Diego County, headquartered in San Diego, which serves people living in Imperial and San Diego counties.
In Northern California, the areas of increased incidence were located within these regional centers’ service zones:
7. The Golden Gate Regional Center, headquartered in San Francisco, which serves Marin and San Mateo counties and the City and County of San Francisco. Two clusters were located within the Golden Gate Regional Center’s service zone; and
8. The San Andreas Regional Center, headquartered in Campbell, Calif., which serves Santa Clara, Santa Cruz, Monterey and San Benito counties.
Two areas of increased incidence were located in Central California regional centers’ service zones:
9. The Central Valley Regional Center, headquartered in Fresno, Calif., which serves Fresno, Kings, Madera, Mariposa, Merced and Tulare counties; and
10. The Valley Mountain Regional Center, headquartered in Stockton, Calif., which serves Amador, Calaveras, San Joaquin, Stanislaus and Tuolumne counties.
Might want to revisit an old Wired piece, The Greek Syndrome, from the early aughts.
