Autism is a developmental disability that impairs the social, emotional, communication, and behavioral development of autistic children. Autistic children may also have abnormal cognitive functioning, learning, attention, and sensory processing.

Studies published before 1985 showed prevalence rates of autism to be 4 to 5 cases per 10,000 children. Since then, non-US studies have indicated higher prevalence rates. However, not much is known about the current prevalence rate of autism in the US because very few population-based studies on this subject have been conducted.

In a study published in the Journal of the American Medical Association , a team of researchers led by scientists from the Centers for Disease Control, have found that autism is about ten times as prevalent today as it was in the 1980s and early 1990s.

About the Study

The researchers determined the prevalence of autism among children aged 3 to 10 years in metropolitan Atlanta, GA in 1996. Screening records from medical and educational centers initially identified cases of suspected or diagnosed autism. Based on these records, medical experts then confirmed whether children met the Diagnostic and Statistical Manual of Mental Disorders, 4th edition definition for autism.

The Findings

Of the 289,456 children aged 3 to 10 living in metropolitan Atlanta in 1996, 987 were determined to have autism. This represented a prevalence rate of 3.4 per 1000, or 34 per 10,000, which is almost 10 times the prevalence found in US studies conducted in the 1980s and early 1990s.

This study examined a racially diverse group of children and found that prevalence rates did not vary significantly by race. However, gender is another story. Boys were four times more likely as girls to be diagnosed with autism.

The authors acknowledge that because cases of autism were determined based on medical records, not an actual examination of the children, the prevalence rates may have been over- or underestimated.

How Does This Affect You?

This study confirms recent concerns that the prevalence of autism in the United States is increasing. However, despite this carefully conducted study, the reasons for this disturbing trend remain incompletely understood.

Part of the increase, according to the study authors, may be due to the fact that the diagnostic criteria for autism have broadened over the past several years. In addition, public awareness of autism has heightened in the 1990s. And in 1991, the US Department of Education added autism as a category of special education services, making it highly likely that more autistic children have been identified.

But an editorial accompanying the autism study states that the increase in prevalence rate cannot be entirely explained by these factors. Though scientists do not know why autism rates are rising, there has been wide speculation that certain environmental conditions may be contributing to the increase. One theory, for example, is that the measles, mumps, and rubella (MMR) vaccine, which is given to virtually all children at roughly the same time that autism is usually diagnosed, is the culprit. A recent article published in the New England Journal of Medicine, however, provided strong evidence to the contrary.

Until more is known about the genetic, and possibly environmental, factors that lead to this distressing condition, there are no known ways for current or expectant parents to prevent autism in their children.