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April 18, 2002
Good afternoon Mr. Chairman, Congressman Waxman, and members of the Committee.
I am Dr. Coleen Boyle, Associate Director for Science and Public Health in the National Center on Birth Defects and Developmental Disabilities at the Centers for Disease Control and Prevention (CDC). I am accompanied by Dr. Melinda Wharton, Director of Epidemiology and Surveillance Division, National Immunization Program, CDC. Thank you for the opportunity to update you today on CDC activities related to autism occurring during the year since your last hearing.
CDC's mission is to promote health and quality of life by preventing and controlling disease, injury, and disability. The Committee requested that CDC testify about prevalence of autism and what we know about the apparent increase in rates. We were also asked to discuss the timeline for implementation of the research recommendations from the Institute of Medicine's evaluation of autism-vaccine related issues and CDC's funding for autism research from FY 1999 to FY 2004. We are prepared to discuss these issues.
The Committee also requested that we address research efforts conducted by CDC into treatments for autism spectrum disorder. CDC has not conducted research into treatment of autism spectrum disorders since National Institutes of Health (NIH) is the agency with responsibility for clinical research.
CDC's Efforts to Track and Evaluate Increased Rates of Autism
Autism spectrum disorders are a group of life-long developmental disabilities caused by an abnormality of the brain. Autism spectrum disorders are characterized by problems with social interaction and communication skills, and by the need for sameness or repetition in behavior. ASD includes autistic disorder, pervasive developmental disorder - not otherwise specified (including atypical autism), and Asperger's disorder.
Since last year's congressional hearing on autism CDC has increased our activities that will contribute to our understanding on the actual prevalence of autism and autism spectrum disorders. Last year I told you about a report of a prevalence study of autism in Brick Township, New Jersey, where there was concern by the local citizens that the number of children with autism in the community seemed unusually high. The investigation found rates of 6.7 and 4.0 per 1,000 children for autism spectrum disorders and autism, respectively. The previously accepted background rate of autism had been about 1-2 per 1,000 children.
This year we can report on the prevalence for autism spectrum disorder in Metropolitan Atlanta from CDC's Metropolitan Atlanta Developmental Disability Surveillance Program (MADDSP). This report shows a prevalence of autism spectrum disorder of 3.4 per 1,000 children. However, we believe that this is a minimum prevalence rate for autism spectrum disorder and that most of the cases are probably autism disorder. The monitoring system in Atlanta is dependent upon the review of school records and the milder cases are not likely to be found in these records. In general, the rate is similar to what was found in Brick Township. We cannot determine whether rates are increasing or not because we do not have comparable data from earlier years.
Our system in Atlanta found that there was no difference in the prevalence of autism spectrum disorder by race. It also showed that 68% of children with autism also have mental retardation.
We cannot yet generalize a prevalence for the US population. The population monitored in Brick was very small, less than 9,000 children. The population monitored in Metropolitan Atlanta is much larger, about 290,000 children, but we cannot assume that it is representative of the U.S. population. Determining if there are regional differences in autism prevalence requires data from other regions of the country.
To address the need for state autism monitoring data, in FY 2000 CDC funded four programs in Arizona, South Carolina, Maryland/Delaware, and New Jersey to establish monitoring and tracking programs for autism. Marshall University in West Virginia has a special autism project funded by CDC which also includes collecting prevalence data. At the end of FY 2001, CDC funded 4 Centers of Excellence in Autism and Pervasive Developmental Disabilities Epidemiology for the purpose of collecting and analyzing information on the prevalence and conducting a collaborative epidemiologic case-control study to identify the causes and preventable risk factors for autism. These centers are located in California, Colorado, Pennsylvania, and Maryland/Delaware. The centers will also collect prevalence data because the database provided by the monitoring program will be used to conduct studies of causes and risk factors for autism.
We have established the Alliance for Research in Child Health and Epidemiology, referred to as ARCHE, which includes both state and center partners who are collecting data on autism. ARCHE members are working together to establish a common case definition and methods to identify children with autism so that data from these programs will be uniform and can be combined for accurate national or regional estimates.
With these programs plus the one CDC conducts in Atlanta, we now have 9 states involved in the effort to monitor the prevalence of autism. We have 4 sites already collecting data for a large epidemiologic study to address possible causes of autism, including the role of genetic and environmental factors in the development of autism. With the new funding we received this year, we expect to add at least 3 programs, bringing the total to 12 states who are tracking autism prevalence.
Surveillance for developmental disabilities provides a number challenges including identifying proper sources of information. Unlike birth defects, developmental disabilities may present themselves later in child development. Thus, the sources required for collecting data on these conditions present greater challenges.
Timeline for implementation of IOM recommended research
CDC continues to take a proactive role in addressing vaccine safety concerns. In 2000, CDC and NIH contracted with the Institute of Medicine (IOM) to establish an independent expert committee to review hypotheses about existing and emerging immunization safety concerns. Some researchers have suggested that the receipt of either the MMR vaccine or thimerosal-containing vaccines has been associated with various neurodevelopmental disabilities including autism, attention deficit disorder, language delay, or speech delay. The IOM was asked to review the available scientific information on these issues. CDC has initiated a broad range of studies to better assess these findings as well as to address recommendations made by the Institute of Medicine (IOM) Immunization Safety Review Committee.
MMR and Autism Studies
In the March 2001 IOM report regarding the association between the MMR vaccine and autism spectrum disorder (ASD), the IOM concluded "the evidence favors rejection of a causal relationship at the population level between MMR vaccine and ASD."
The IOM made several recommendations regarding future research including the following epidemiological studies:
CDC is currently funding three research studies that address the above four recommendations from the IOM. The first study, the Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP) MMR/Autism Study, is a large case-control study. The autism cases for the study were identified through MADDSP. The control subjects were selected from the same or similar schools in the Atlanta area and matched to cases based on age and gender. The study is assessing the relationship between the timing of receipt of the first MMR vaccine and risk for developing autism. In addition, several subgroup analyses are being carried out, including analyses using isolated and non-isolated autism cases as well as analyses examining cases with and without pre-existing conditions. The analyses for this study and a manuscript should be completed by early fall 2002.
The second study is the MMR/Regression Autism Study funded by CDC and the National Institutes of Child Health and Human Development (NICHD). This is also a large case-control study that is using a sample of autism cases identified as part of the NICHD 10 Collaborative Programs of Excellence in Autism (CPEA). This study is specifically designed to examine the association between regression autism and the timing of first receipt of the MMR vaccine. The study is being carried out over a three-year period and is designed to test whether or not regressive autism is triggered by receipt of the MMR vaccine. Results from this study are expected in the spring of 2004.
The third study, the Denmark MMR/Autism Study, is a recent study that was carried out in Denmark in collaboration with CDC. The study was designed to follow-up on approximately 537,000 children born in Denmark during the period from January 1, 1991 to December 31, 1998. Of these, 82% received MMR vaccine. The cohort was generated based on data obtained from the Danish Civil Registration System (CRS) and subsequently linked with other national registries. The manuscript is expected to be submitted for publication in 2002.
Finally, CDC is in the early stages of planning a study to investigate whether or not measles vaccine-strain virus is present in the intestines of some children with ASD.
Reports dealing with the findings of measles virus sequences in intestinal biopsies from children with autistic disorder have raised some concern. To resolve differences in previous studies that may have occurred due to study design, sampling biases, and differences in laboratory assays used and in assay sensitivity, an independent, multicenter study is being designed. This study plan is to determine the prevalence of measles virus vaccine strain gene sequences in bowel biopsy tissue from children with gastrointestinal tract complaints with and without autistic disorder. The study would be designed to ensure use of standardized clinical and laboratory protocols, appropriate enrollment of controls, blinding of specimens, use of standardized laboratory reagents and assays, and appropriate statistical evaluation.
Thimerosal and Neurodevelopmental Delay Studies
In October 2001, the IOM Immunization Safety Review Committee published a report on the possible association between thimerosal-containing vaccines and neurodevelopmental disorders. In this report, the IOM concluded "that the evidence is inadequate to accept or reject a causal relationship between exposure to thimerosal from vaccines and the neurodevelopmental disorders of autism, ADHD, and speech or language delay." Of course, ADHD is attention deficit hyperactively disorder. The IOM made several recommendations regarding future research studies including the following epidemiological studies:
CDC has undertaken several studies that address these recommendations. The first study, the Thimerosal Screening Analysis, is an ongoing study that was started in the fall of 1999. CDC used the large automated databases that link vaccination and International Classification of Disease codes (ICD-9) stored in the medical records in the Vaccine Safety Datalink (VSD) project, to screen for possible associations between exposure to thimerosal-containing vaccines and a variety of neurologic and developmental problems. In the first phase of this study, the CDC used data from 2 of the managed care organizations within the VSD, and CDC and VSD researchers found statistically significant associations between thimerosal and several neurodevelopmental disorders, including language delays, speech delays, ADHD, unspecified developmental delays, stuttering, sleep disorders, emotional disorders, and tics. However, the associations were not consistent between the two HMOs. In the second phase of the investigation, CDC investigators examined data from a third managed care organization. Analyses of these data using the same methods as the first study did not confirm results for speech or language delay and attention deficit disorder. The data were not available to study tics or other unspecified developmental delays. A statistically significant relationship between autism and thimerosal was not found in either the preliminary study or the later, larger analysis. This study will be submitted for publication in 2002.
The second study is the Thimerosal Follow-Up Study, which is being designed to assess whether preliminary results from automated data used in the Thimerosal Screening Analysis can be confirmed using objective neuropsychological testing. The study will focus on the conditions found in the first screening analyses, including language and speech delays and ADHD. The design of the new study will address the main drawback of the Thimerosal Screening Analysis, which was that children were not objectively assessed on the neurodevelopmental disorders of interest. The various VSD HMOs categorize neurodevelopmental disabilities in different ways, provide different services for these disorders, and often refer children out of the health care network when they are identified with these particular disorders. Therefore, the Thimerosal Follow-Up Study is planned to examine approximately 1200 children between the ages of 7 and 9 years of age randomly selected from four VSD HMOs based on thimerosal exposure during the first 3 months of life. All 1200 children will be brought into their respective HMOs and will be assessed using a standardized set of neuropsychological test batteries. The preliminary proposal for this study was presented to a panel of external consultants including a consumer representative in March of 2001. In September of 2001, CDC awarded a contract to Abt Associates Inc. to carry out the planning phase of the study. The panel of external consultants continues to provide individual input into the study design and the planning phase should be completed by June 2002. Data collection is expected to begin in the latter half of 2002. Abt Associates Inc. is expected to present the results of the study by the end of 2003.
Several additional studies are being planned to address additional concerns raised by the IOM.
The Thimerosal/Autism Study is planned to be a case-control study to be conducted simultaneously with the Thimerosal Follow-up Study. Autism cases identified through review of automated medical records will be assessed objectively by using a standardized autism assessment tool. Controls will be selected from the Thimerosal Follow-up Study and matched to cases by age and sex.
Two other studies being planned will examine changes over time in the diagnosis of neurodevelopmental delays including autism. These studies will use inpatient and outpatient discharge diagnoses to compare rates of these conditions over time with changes in levels of thimerosal in recommended childhood vaccines. Because recommendations for the removal of thimerosal from vaccines did not occur until 1999, several years of data following the removal of thimerosal will be necessary before these comparisons can be made. Thus, results will not be available until 2005 or later.
CDC funding for autism research from FY 1999 through FY 2004
The CDC spent the following amounts on autism research: $943,000 in FY 1999, $2.6 million in FY 2000, $8.3 million in FY 2001, and plans to spend $11.3 million in FY 2002 and $10.2 million in FY 2003. Plans for FY 2004 have not yet been developed.
CDC remains committed to collecting accurate data on prevalence of autism and conducting studies to find causes of autism. Research is already underway, and more is planned, to look at the relationship between the MMR vaccine and autism. We want each child to be born healthy and to grow and develop normally, so that they are able to lead productive lives. We are dedicated to finding the answer to what causes autism and how it can be prevented. We will continue our work until the answer is known.
Thank you for the opportunity to tell you about CDC's efforts on autism. At this time, I would be happy to answer your questions.
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Last revised: April 29, 2002