Why is Autism Incidence Still Increasing?
The incidence of autism may be much higher than previously thought in the United States and elsewhere in the world, according to a recent rigorous, comprehensive study of the autism condition, conducted in South Korea. In the first ever attempt to take a broad-based look at an entire population for the prevalence of autism spectrum disorders - and all types of autism ranging from severe symptoms to the milder Asperger's syndrome - researchers found a rate of 2.64% among South Korean children. That's an incidence rate of 1 in 38 children, a rate far higher than the estimate of 1 in 110 children for the U.S., published by the Centers for Disease Control and Prevention (CDC).
A five-year study,("Prevalence of Autism Spectrum Disorders in a Total Population Sample", published in the American Journal of Psychiatry by Y.S. Kim et al., May 9, 2011 [doi:10.1176/appi.ajp.2011.10101532]) funded partly by Autism Speaks, and led by Dr. Young Shin Kim of the Yale Child Study Center, differed significantly in methodology from earlier autism-prevalence studies. Because of the different methodology used, different findings on ASD were obtained, and this likely accounts for the dramatically different findings, compared to other epidemiological studies, Dr. Kim said.
In recent years, studies of autism spectrum disorder (ASD) in the U.S. have reported a steady increase in incidence, from 1 in 5,000 in 1975 to 1 in 110 in 2009. Since autism was first identified, ideas about its cause have swung to and fro between genetics and environment as the prime causative factor. Quite recently, several major federally funded trials have been started, together with other research studies, now under way in the United States to attempt to finally determine what the determining factor is in making a child autistic.
In the meantime, epidemiological studies of ASD have been conducted, in an attempt to determine if the observed incidence of ASD is steady year after year, or is climbing due to some unknown environmental or cultural factor. No definitive answer on the ultimate origin of ASD has yet emerged. Although this may be an intractable question, it is important to attempt to find an answer as to why ASD incidence rates keep rising. Several environmental risk factors have been proposed to support the hypothesis that the actual frequency of autism has increased. These include: certain foods, infectious disease, pesticides, MMR vaccine, and vaccines containing the preservative thiomersal, formerly used in several childhood vaccines in the U.S. Although there is overwhelming scientific evidence against the MMR hypothesis, and no convincing evidence for the thiomersal hypothesis, other as-yet-unidentified environmental risk factors cannot be ruled out. Thus there is a need for accurate epidemiological studies to pin down what is the genesis of childhood ASD.
Previous studies assessing population-wide autism rates typically focused on high-risk populations - such as classrooms of special education students. In contrast, the South Korean study assessed more than 55,000 children, ages 7 to 12, not only from mental health service organizations and special education classrooms, but also regular schools. In the study's conclusion, it was stated: "Two-thirds of ASD cases in the overall sample were in the mainstream school population, undiagnosed and untreated. These findings suggest that rigorous screening and comprehensive population coverage are necessary to produce more accurate ASD prevalence estimates and underscore the need for better detection, assessment, and services."
Using several diagnostic techniques and measures to evaluate the incidence in children, the ASD study found that the observed rates of autism spectrum disorder among the children in special education and mental health services programs were very similar to estimates elsewhere in the world - from 0.6% to 1.8% of the population. Dr. Kim said children in regular American classrooms ought to be included in future ASD studies, so as to get a better measure of the incidence of autism spectrum disorders. If that were done, she added, the prevalence of the condition in the U.S. and other countries also would be in the range of 2% to 3%, in line with the ASD incidence found in South Korea, 2.6%.
"This study clearly confirms that autism is a significant, global, public health concern that transcends cultural, ethnic and geographic boundaries," Dr. Kim said. "We do need to do this type of study in the U.S. ... Until we do, we won't know what the population prevalence is."
More children than ever before are being diagnosed with an Autism Spectrum Disorder. It is unclear how much of this increase is due to a broader definition of ASDs and better efforts in diagnosis. However, a true increase in the number of people with an ASD, likewise cannot be ruled out. Probably the observed increase in ASD diagnosis is due to a combination of these factors.
A five-year study,("Prevalence of Autism Spectrum Disorders in a Total Population Sample", published in the American Journal of Psychiatry by Y.S. Kim et al., May 9, 2011 [doi:10.1176/appi.ajp.2011.10101532]) funded partly by Autism Speaks, and led by Dr. Young Shin Kim of the Yale Child Study Center, differed significantly in methodology from earlier autism-prevalence studies. Because of the different methodology used, different findings on ASD were obtained, and this likely accounts for the dramatically different findings, compared to other epidemiological studies, Dr. Kim said.
In recent years, studies of autism spectrum disorder (ASD) in the U.S. have reported a steady increase in incidence, from 1 in 5,000 in 1975 to 1 in 110 in 2009. Since autism was first identified, ideas about its cause have swung to and fro between genetics and environment as the prime causative factor. Quite recently, several major federally funded trials have been started, together with other research studies, now under way in the United States to attempt to finally determine what the determining factor is in making a child autistic.
In the meantime, epidemiological studies of ASD have been conducted, in an attempt to determine if the observed incidence of ASD is steady year after year, or is climbing due to some unknown environmental or cultural factor. No definitive answer on the ultimate origin of ASD has yet emerged. Although this may be an intractable question, it is important to attempt to find an answer as to why ASD incidence rates keep rising. Several environmental risk factors have been proposed to support the hypothesis that the actual frequency of autism has increased. These include: certain foods, infectious disease, pesticides, MMR vaccine, and vaccines containing the preservative thiomersal, formerly used in several childhood vaccines in the U.S. Although there is overwhelming scientific evidence against the MMR hypothesis, and no convincing evidence for the thiomersal hypothesis, other as-yet-unidentified environmental risk factors cannot be ruled out. Thus there is a need for accurate epidemiological studies to pin down what is the genesis of childhood ASD.
Previous studies assessing population-wide autism rates typically focused on high-risk populations - such as classrooms of special education students. In contrast, the South Korean study assessed more than 55,000 children, ages 7 to 12, not only from mental health service organizations and special education classrooms, but also regular schools. In the study's conclusion, it was stated: "Two-thirds of ASD cases in the overall sample were in the mainstream school population, undiagnosed and untreated. These findings suggest that rigorous screening and comprehensive population coverage are necessary to produce more accurate ASD prevalence estimates and underscore the need for better detection, assessment, and services."
Using several diagnostic techniques and measures to evaluate the incidence in children, the ASD study found that the observed rates of autism spectrum disorder among the children in special education and mental health services programs were very similar to estimates elsewhere in the world - from 0.6% to 1.8% of the population. Dr. Kim said children in regular American classrooms ought to be included in future ASD studies, so as to get a better measure of the incidence of autism spectrum disorders. If that were done, she added, the prevalence of the condition in the U.S. and other countries also would be in the range of 2% to 3%, in line with the ASD incidence found in South Korea, 2.6%.
"This study clearly confirms that autism is a significant, global, public health concern that transcends cultural, ethnic and geographic boundaries," Dr. Kim said. "We do need to do this type of study in the U.S. ... Until we do, we won't know what the population prevalence is."
More children than ever before are being diagnosed with an Autism Spectrum Disorder. It is unclear how much of this increase is due to a broader definition of ASDs and better efforts in diagnosis. However, a true increase in the number of people with an ASD, likewise cannot be ruled out. Probably the observed increase in ASD diagnosis is due to a combination of these factors.
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