The results of a new study confirm the findings of a controversial 2006 paper entitled “Does Television Cause Autism?” The study suggests that counties with higher precipitation levels also have higher autism rates. The 2006 paper added another element on the list of conditions: the number of homes with cable TV. According to the article, countries with higher precipitation levels and higher percentages of homes with cable TV had higher autism rates.

U.S. researchers at Cornell University analyzed autism rates from state and county agencies for children born in California, Oregon and Washington between 1987 and 1999 and plotted them against daily precipitation reports in an attempt to find an environmental link with autism, a disability that affects the child’s ability to communicate and interact with others. They also looked at the average annual precipitation in the counties when the children were younger than 3, the period during which autism is generally diagnosed.

“Autism prevalence rates for school-aged children in California, Oregon and Washington in 2005 were positively related to the amount of precipitation these counties received from 1987 through 2001,” the researchers wrote in the Archives of Pediatrics & Adolescent Medicine. They added that counties in Oregon and Washington west of the Cascades, where the amount of precipitation is four times higher than counties east of the Cascades, register an autism rate that is twice as high. Those children diagnosed with autism would have been under 3 during the periods of high precipitation, the period during which autism is generally diagnosed.

But the precipitation itself it’s not the only one to blame for autism. The precipitation is one of the factors associated to indoor activity, such as TV viewing, chemical exposure to indoor substances, and vitamin D deficiency from too little sunlight. All these activities that children do at home on rainy days may lead to autism because they affect their cognitive development.

“Finally, there is also the possibility that precipitation itself is more directly involved,” the researchers wrote. For instance, chemicals in the upper atmosphere may be transported to the surface by the rain.

The U.S. Centers for Disease Control and Prevention estimates that about one in every 150 children has autism, a disability which typically appears during the first years of life, or a related disorder such as Asperger's Syndrome. Studies have shown that males are four times more likely to have autism than females. The rising rate of autism has also been attributed to improvements in the way doctors are able to recognise the disorder.

There is no single cause of autism, whose symptoms range from severe social avoidance to repetitive behaviors and sometimes profound mental retardation, and most doctors believe is no cure. Doctors agree there is a genetic component to autism, but many of them are skeptical when it comes to the hypothesis that environmental factors may trigger autism.

However, researchers call for more research to see if the link is a real one and establish whether such an environmental trigger exists.