California Autism Diagnoses Accelerated for Children Born in 2016

Cynthia Nevison and Walter Zahorodny examined California Department of Developmental Services records across the 36 most populous counties. Diagnosed autism spectrum disorder prevalence rose among every race and ethnicity group they tracked. The acceleration was clearest for children born in the mid-2010s, most often birth year 2016, and it was strongest in lower- and middle-income counties. Statewide, the estimated rate for children born in 2019 was 3.9 percent, against 1.5 percent for those born in 2013. For 2019 births the figures were 6.0 percent among Black children, 3.4 percent among Hispanic children, 3.0 percent among Asian children, and 2.7 percent among white children. In nine counties with enough data, Black children’s rates ran higher than the other groups. Los Angeles County approached 9.5 percent for Black children in one recent year; Sacramento, Fresno, and Kern were near 8 percent.

Statewide averages smooth the break. When the authors split the data by county and by race, the 2016 birth-year shift stood out. In lower-income counties, rates for white and Hispanic children had already been rising among children born between 2000 and 2014. After 2015 the slope steepened. For children born in 2020 the estimates reached 8.7 percent for white children in Butte County and 4.9 percent for Hispanic children in Fresno and Tulare. Nevison told The Defender the evidence of a changepoint across many locations was “surprisingly crisp.” She said the numbers match what teachers in California autism classrooms have described: more students with more severe behaviors, staff burnout, and open positions. “The data in my paper suggest that the perception of my teacher friends is correct,” she said. She also noted that the children who appear most severely affected are often those whose families have the least capacity to absorb extra costs for food or therapies.

The authors did not test causes. They wrote that autism appears to result from “a complex interaction of genetic factors and early environmental insults” that can produce neuroinflammation, immune dysregulation, and oxidative stress during early brain development. They concluded that “understanding the factors driving diagnosed ASD prevalence up to the high levels reported in this study is a pressing public health concern.” They did not name those factors. Comparing their DDS numbers with federal Autism and Developmental Disabilities Monitoring Network figures, they estimated that California’s system may capture only about half of cases, so the true rates are higher. The CDC’s latest ADDM snapshot still rests on children born in 2014, when the national figure for 8-year-olds was about 1 in 31. California sites in that system have run higher than other states.

Children’s Health Defense Chief Scientific Officer Brian Hooker observed that California Senate Bill 277 took effect on January 1, 2016. The law removed personal-belief and religious exemptions for school and childcare immunization requirements. The birth-year changepoint Nevison and Zahorodny identified sits in the same calendar year. The study itself does not measure vaccination status or exemption rates. Karl Jablonowski, a senior research scientist at Children’s Health Defense, said the data show no tapering yet. “If there is an end to the autism explosion, we can’t see it yet,” he said. He described the authors’ “pressing public health concern” phrasing as academic language for an increase whose drivers remain unexamined at the scale the numbers now require.

The paper’s usable claim is narrower than any single explanation. Diagnosed prevalence in California’s developmental-services system rose across groups, accelerated for children born around 2016, and rose fastest where household resources are lower. The authors say the factors behind those levels need investigation. The investigation has not been done in this dataset.