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DAVIS, Calif. — What causes autism? The question has spurred about a billion dollars’ worth of genetics research that has found no clear answer.

But University of California, Davis, epidemiologist Irva Hertz-Picciotto has been pursuing another angle: Does the environment around a pregnant woman play a role in determining whether her child develops autism?

Over the last 10 years, her work with more than 1,000 autistic children has changed how science looks at autism, refocusing the debate on the crossroads of environment and genetics.

Hertz-Picciotto’s group has published hundreds of papers, including one that suggests, among other things, that a mother’s proximity to congested roads and, thus, dirty air increases her risk of giving birth to an autistic child. Her group more recently suggested that obese women may be 67 percent more likely to have autistic children.

Those findings have raised the profile of Hertz-Picciotto and UC Davis’ autism institute as parents have seen autism rates soar and look for anything they can do to prevent their children from developing the disorder. The Centers for Disease Control and Prevention said last year that 1 in 88 U.S. children has an autism disorder, a 23 percent jump since 2009 (Greenwire, March 29, 2012).

Alycia Halladay, a senior director at the advocacy group Autism Speaks, called Hertz-Picciotto a “pioneer.” Without Hertz-Picciotto’s work, she said, it would have taken years for environmental factors to emerge as a focus of research.

“Not only is she a pioneer,” Halladay said, “but she really continues to be one of the major leaders in this area. If you think about the scope of her research, she is involved in all things involving environmental epidemiology of autism.”

Hertz-Picciotto, who knew little about autism when she began her research more than a decade ago, said her objective is ostensibly simple.