Diagnoses of Autism Wikipedia"The study took place in California, where autism cases handled by the state's department of developmental services increased 636 percent from 1987 to 2003, according to Science Daily. The Columbia University team studied data from more than 300,000 children born in California between 1997 and 2003, and found that children who live within 250 meters of a child with autism have a 42 percent higher chance of being diagnosed with an autism spectrum disorder with the next 12 months. Children who live 250 to 500 meters away have a 22 percent higher chance of being diagnosed, and the greater the distance the less the likelihood of a diagnosis. The 'social effect' was more prevalent in cases of mild (or 'high functioning') autism diagnoses."
Autism Awareness: Is proximity a factor in diagnosing autism? - Child Caring - Boston.com