The number of cases of autism spectrum disorder (ASD) has risen sharply, according to a new study published by the Centers for Disease Control and Prevention (CDC).
The finding was based on a 2008 survey of 300,000 children 8 years old from 14 communities across the country. The total number of children estimated to carry the diagnosis (ASD prevalence) has increased by 23% since 2006, and 78% since an initial 2002 survey.
The numbers seem alarming, but the CDC is quick to note some important limitations to their report that could temper the findings.
ASDs are almost five times more common among boys than girls, accounting for a ratio of 1 case of ASD in every 54 boys. The combined ratio for boys and girls has jumped from 1 in 150 children in 2002, to 1 in 125 in 2004, 1 in 110 in 2006, and 1 in 88 based on the 2008 data. The study also shows that more children are being diagnosed at an earlier age, which allows for earlier therapeutic intervention.
The Children?s Health Act of 2000 authorized the CDC to create the Autism and Developmental Disabilities Monitoring (ADDM) Network. Its purpose was to collect data that would provide estimates of the prevalence of ASDs across the country and identify higher risk groups that might better direct funding initiatives and therapeutic interventions. Fourteen states participate in the network, from Arizona to New Jersey.
The 14 network participants were selected through a competitive review process on the basis of their ability to conduct surveillance of ASDs. They weren?t selected to be a nationally representative sample. Therefore, it?s not clear that the results can be extrapolated to the country as a whole.
For the purposes of the study, a child was considered to meet the case definition for ASD if he or she displayed behaviors consistent with the American Psychiatric Association?s Diagnostic Manual criteria for the following conditions: Autistic Disorder; Pervasive Developmental Disorder ? Not Otherwise Specified, including Atypical Autism; or Asperger Disorder.
These criteria leave a lot of room for researchers to include milder cases of Asperger or diverse developmental problems along with more severe autistic disorders, potentially resulting in the overestimating the number of ASD diagnoses. The study was also based on data extracted from medical records and not from direct observation and diagnosis by a trained professional.? A previous study in England based on chart review resulted in significant over-diagnosis of the disorder. Moreover, CDC notes there was variability in chart review methods between the 14 study sites.
There are no medical or blood tests for diagnosing ASD, rendering the diagnosis quite difficult at times.? Sometimes ASDs can be detected at 18 months. An experienced professional can make a reliable diagnosis by age 2.
However, many children aren?t diagnosed until much later. Most will be diagnosed by age 8, so the CDC selected that age for the basis of its ASD prevalence reporting.
Although primary-care pediatricians are capable of making the diagnosis, cases are often referred to specialists due to the complexity of the assessments required.? Trained professionals will examine the developmental and behavioral history, and may also include hearing and vision screening, genetic testing, neurological testing, and other medical tests.
The CDC notes that the survey wasn?t designed to determine the causes for the increase in ASD prevalence. The rapid rise of reported ASD rates between 2002 and 2008 strongly suggests that study methodology and increased awareness and reporting of ASD-related conditions are the major contributing factors.
While environmental and genetic factors are possible contributors, it?s highly unlikely they are significant.
If you?re a concerned parent, the best advice is to make sure your child has regular check-ups with his/her pediatrician or family doctor in order to properly assess developmental milestones. If developmental delays or behavioral challenges are identified, then further testing will be necessary.
Remember, the most likely cause of increased prevalence of ASDs is enhanced awareness and detection along with the inclusion of broad diagnostic criteria. ?No changes to your child?s routine diet, environmental exposure, or activity are suggested.
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