The CDC's autism numbers game

Elizabeth McBreen


When the 2009 Autism and Developmental Disabilities Monitoring (ADDM) report was released just before Christmas last year, it reported a staggering 57 percent increase in prevalence of autism spectrum disorders (ASDs) between 2002 and 2006.

The rate of children with an ASD is now 1 in 110 or nearly one percent. The rate is as high as 1 in 70 among boys.

Catherine Rice, Ph.D., is a behavioral scientist at the National Center on Birth Defects and Developmental Disabilities (NCBDDD) at the Centers for Disease Control and Prevention (CDC). Rice announced the release of the report on Dec. 18 at a media briefing. She also presented key findings at an Interagency Autism Coordinating Committee (IACC) in January. Rice says that the CDC is doing its best to report autism prevalence in a timely manner. But in the face of this exploding epidemic, some in the autism community question the method and urgency of federal agencies.

The method that the CDC utilizes is an active form of case finding, according to Rice, as opposed to voluntary reports submitted by regional health departments. Medical evaluations and records from sites that educated, diagnosed, treated and provided services are the primary source of information for the report. Educational records are not available at all the sites. Rice says the CDC cannot require educational records be available at surveillance sites since they are not part of the public health record. The report’s authors admit that this is a shortcoming in process of finding true prevalence, “Some sites across the network partnered with both health care and education providers, while others work solely with health care providers. Sites that worked with both types of providers tended to have higher prevalence estimates because they had access to additional information to help identify children with ASDs.”

Lyn Redwood, RN, MSN, NP of SafeMinds and public member of IACC says that the CDC should make educational records a requirement for surveillance sites. Redwood says it is unacceptable for the CDC to acknowledge such inadequacies in ADDM’s study design, “but seem perfectly willing to accept it as the status quo without any desire to do a better job.”

According to the ADDM report, surveillance sites, which are certain counties within states, collaborate to ensure the consistency of their methods, which are based on CDC’s Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP). MADDSP tracks the developmental disabilities among 8-year-olds in Atlanta and the surrounding metro area.

Once all the records are gathered, clinicians read through them individually using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) to determine whether each child meets the diagnosis for a developmental disability. Rice admits that the method is not perfect, “We are making assumptions some of the time. It is not right 100 percent of the time.” Eight-year-olds are the focus of the report because it is assumed that by age 8, a child with developmental problems will have been evaluated. Mark Blaxill is the director of SafeMinds and editor-at-large of Age of Autism, a daily internet newspaper. He says that gathering geographical and temporal surveillance is critical for tracking prevalence and that better methods are in place for other diseases, “There is mandatory national reporting for the measles, mumps, and deaths from the flu, but not for autism. Even in the states that are in the ADDM network, they are only looking at a small part of each state. We need mandatory autism reporting from each state. That would provide the most valuable environmental tool you could imagine.”

An open call is put out by the CDC to state departments to choose the sites that will take part in the ADDM report. An independent panel reviews the applications, considers the population size of the counties and ensures that the sites will be able to provide the necessary records. Once a site is chosen, it is funded by the CDC for cycles of four to five years at a time. Within the community there is concern about consistency as far as surveillance sites. Rice says that the CDC cannot fund the sites indefinitely. Again, Redwood disagrees with the CDC’s method and says it should change. “It is so critical to maintain consistency in tracking this condition over time in a consistent population.” New Jersey, the state with the highest autism prevalence in the country, was included in the first two ADDM reports but removed from the 2006 study. Blaxill says that changing surveillance sites automatically biases the data, “They need to compare apples to apples, but they are purposely changing the sites. They just need to do something consistent.”

Currently, there is a three-year lag in the release of the ADDM data. Rice says that the CDC is working to reduce this gap. “We are trying to reconstruct cohorts over time. We need annual records to do that, so the report will never be released in the same year that the data was collected.”

When the data is collected, diagnoses are divided into subtypes and the proportions of autism as opposed to other autism spectrum disorders are considered. Rice says that 47 percent of the children in 2009 report had autism. Blaxill says this is an astonishing admission. One that is not included in the ADDM report. “They say that the numbers went up because the definition of Asperger’s syndrome was broadened in the DSM-IV. By failing to include those subgroups, they lose the opportunity to test whether that argument makes any sense at all.”

But Rice says that differentiating the disorders is not always the best indicator of severity. “Another way to look at it is cognitive development. Forty-one percent of the children evaluated in 2006 had an intellectual disability, so the majority are operating at an average or above average level. That’s encouraging.” This figure is a slight improvement from two years prior. In 2004, 43 percent of children evaluated had an intellectual disability, or an IQ below 70. Rice cautions though, that cognitive development can also be misleading, “A child can be smart and be very impaired. But it’s encouraging to see that cognitive problems went down over all.” Eventually, clinical impressions will be added to the report, “that will provide more information as far as severity,” says Rice. Differentiating between ASDs may not dictate severity, but it is one indicator, says Blaxill. “There is no reason not to disclose subgroups just because they are not the only markers of severity. They ought to include more information, not less.”

The CDC has requested site applicants in order to conduct a prevalence study on adults. So far, Rice says that appropriate sites have not been identified, but it is a study the agency is interested in conducting in the future.

The timing of the report’s release, on the Friday before Christmas, angered many in the community. Some felt the CDC was trying to bury the numbers. Rice says that the release was out of the authors’ hands once they had met all editorial and publishing deadlines. “It would have been easier to release it in January, but we felt it was important to release it in 2009, as soon as possible.”
As far as finding a cause for autism and its rapid increase in prevalence, Rice says that one of the major challenges of autism research is that there is not one cause. “There’s a genetic base, but we have to look at how genes and the environment interact, and the environment is very broad. It is basically everything that is not genetic.” Rice says that there has been a revolution in genetic studies in the past 10 years, “We need to have a revolution like that in environmental studies.”

One of the largest studies currently underway that to identify environmental risk factors for developmental disabilities is the Study to Explore Early Development (SEED) study. SEED is being conducted by the Centers for Autism and Developmental Disabilities Research and Epidemiology (CADDRE) Network established by the CDC. “The SEED study is looking at a variety of environmental factors,” says Rice, “things that could have affected the child early on, auto immune issues, medications taken during pregnancy. We need to understand the trajectory of what happens to these children. There are GI and sleep issues that we do not understand. We need a full medical background of these children.” Rice says that right now, chemicals are a big concern in terms of environmental factors.

Rice attended the January IACC meeting to review key findings in the ADDM report with the committee. Tom Insel, M.D., director of the National Institutes of Mental Health (NIMH) is the chair of IACC. He says that whether the increase of autism prevalence reflected in the ADDM report is a true increase is a difficult question to answer, since the report is lacking clinical assessments. This is a deficit that Rice is hoping to rectify in coming years.

In an effort to answer this difficult question though, Insel points to the data from the 2009 U.C. Davis Medical Investigation of Neurodevelopmental Disorders (M.I.N.D.) Institute study, saying, “At least from attempts to look at California, we can’t dismiss it (increased prevalence) as being related to ascertainment. The burden of proof is on anyone who doesn’t think there’s a real increase.” The California study found that one tenth of the increased prevalence in the state was due to the inclusion of milder cases of autism spectrum disorders and 24 percent was due to better diagnosis. Well over half of the increase could not be explained by diagnostic or social causes, such as an influx of immigrants into the state.

Insel also agrees with Rice’s statement that there is more than one cause of autism. He also feels that autism is “most certainly more than one disorder. We still do not understand all the disorders that are called autism.” Insel says that environmental research is an important area for autism research, but the challenge is developing tools that are sophisticated enough to do the work. “Now, in 2010, our environmental tools are not as strong as the genetic tools we have. This could be why there is more genetic research going on.” Redwood believes that the problem is lack of leadership. “If they place an emphasis on the environment and call for specific requests for applications to develop those tools, it will happen,” says Redwood. She also says that all genetic studies should include more environmental phenotyping and that it should be made a requirement that all funding address both genes and environmental exposures.

Courtesy of Spectrum Publications


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