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Academic Study Template | Autism Spectrum | Autism

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Prevalence of Autism Spectrum Disorders — Autism and Developmental Disabilities Monitoring Network, 14 Sites, United States, 2008 Surveillance Summaries March 30, 2012 / 61(SS03);1-19 Autism and Developmental Disabilities Monitoring Network Surveillance Year 2008 Principal Investigators Corresponding author: Jon Baio, EdS, National Center on Birth Defects and Developmental Disabilities, CDC, 1600 Clifton Road, MS E-86, Atlanta, GA 30333. Telephone: 404-498-3873; Fax: 404-498-3550; E-mail: jbaio@
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  Prevalence of Autism Spectrum Disorders — Autism and Developmental DisabilitiesMonitoring Network, 14 Sites, United States,2008  Surveillance Summaries March 30, 2012 / 61(SS03);1-19 Autism and Developmental Disabilities Monitoring Network Surveillance Year 2008 PrincipalInvestigators Corresponding author: Jon Baio, EdS, National Center on Birth Defects and DevelopmentalDisabilities, CDC, 1600 Clifton Road, MS E-86, Atlanta, GA 30333. Telephone: 404-498-3873; Fax:404-498-3550; E-mail: jbaio@cdc.gov. Abstract Problem/Condition: Autism spectrum disorders (ASDs) are a group of developmental disabilitiescharacterized by impairments in social interaction and communication and by restricted, repetitive, andstereotyped patterns of behavior. Symptoms typically are apparent before age 3 years. The complexnature of these disorders, coupled with a lack of biologic markers for diagnosis and changes in clinicaldefinitions over time, creates challenges in monitoring the prevalence of ASDs. Accurate reporting of data is essential to understand the prevalence of ASDs in the population and can help direct research. Period Covered: 2008. Description of System: The Autism and Developmental Disabilities Monitoring (ADDM) Network is anactive surveillance system that estimates the prevalence of ASDs and describes other characteristicsamong children aged 8 years whose parents or guardians reside within 14 ADDM sites in the UnitedStates. ADDM does not rely on professional or family reporting of an existing ASD diagnosis or classification to ascertain case status. Instead, information is obtained from children's evaluation recordsto determine the presence of ASD symptoms at any time from birth through the end of the year when thechild reaches age 8 years. ADDM focuses on children aged 8 years because a baseline study conducted by CDC demonstrated that this is the age of identified peak prevalence. A child is included as meeting thesurveillance case definition for an ASD if he or she displays behaviors (as described on a comprehensiveevaluation completed by a qualified professional) consistent with the American Psychiatric Association'sDiagnostic and Statistical Manual-IV, Text Revision (DSM-IV-TR) diagnostic criteria for any of thefollowing conditions: Autistic Disorder; Pervasive Developmental Disorder–Not Otherwise Specified(PDD-NOS, including Atypical Autism); or Asperger Disorder. The first phase of the ADDMmethodology involves screening and abstraction of comprehensive evaluations completed by professional   providers at multiple data sources in the community. Multiple data sources are included, ranging fromgeneral pediatric health clinics to specialized programs for children with developmental disabilities. Inaddition, many ADDM sites also review and abstract records of children receiving special educationservices in public schools. In the second phase of the study, all abstracted evaluations are reviewed bytrained clinicians to determine ASD case status. Because the case definition and surveillance methodshave remained consistent across all ADDM surveillance years to date, comparisons to results for earlier surveillance years can be made. This report provides updated ASD prevalence estimates from the 2008surveillance year, representing 14 ADDM areas in the United States. In addition to prevalence estimates,characteristics of the population of children with ASDs are described, as well as detailed comparisons of the 2008 surveillance year findings with those for the 2002 and 2006 surveillance years. Results: For 2008, the overall estimated prevalence of ASDs among the 14 ADDM sites was 11.3 per 1,000 (one in 88) children aged 8 years who were living in these communities during 2008. Overall ASD prevalence estimates varied widely across all sites (range: 4.8–21.2 per 1,000 children aged 8 years).ASD prevalence estimates also varied widely by sex and by racial/ethnic group. Approximately one in 54 boys and one in 252 girls living in the ADDM Network communities were identified as having ASDs.Comparison of 2008 findings with those for earlier surveillance years indicated an increase in estimatedASD prevalence of 23% when the 2008 data were compared with the data for 2006 (from 9.0 per 1,000children aged 8 years in 2006 to 11.0 in 2008 for the 11 sites that provided data for both surveillanceyears) and an estimated increase of 78% when the 2008 data were compared with the data for 2002 (from6.4 per 1,000 children aged 8 years in 2002 to 11.4 in 2008 for the 13 sites that provided data for bothsurveillance years). Because the ADDM Network sites do not make up a nationally representativesample, these combined prevalence estimates should not be generalized to the United States as a whole. Interpretation: These data confirm that the estimated prevalence of ASDs identified in the ADDMnetwork surveillance populations continues to increase. The extent to which these increases reflect better case ascertainment as a result of increases in awareness and access to services or true increases in prevalence of ASD symptoms is not known. ASDs continue to be an important public health concern inthe United States, underscoring the need for continued resources to identify potential risk factors and to provide essential supports for persons with ASDs and their families. Public Health Action: Given substantial increases in ASD prevalence estimates over a relatively short period, overall and within various subgroups of the population, continued monitoring is needed toquantify and understand these patterns. With 5 biennial surveillance years completed in the past decade,the ADDM Network continues to monitor prevalence and characteristics of ASDs and other developmental disabilities for the 2010 surveillance year. Further work is needed to evaluate multiplefactors contributing to increases in estimated ASD prevalence over time. ADDM Network investigatorscontinue to explore these factors, with a focus on understanding disparities in the identification of ASDsamong certain subgroups and on how these disparities have contributed to changes in the estimated prevalence of ASDs. CDC is partnering with other federal and private partners in a coordinated responseto identify risk factors for ASDs and to meet the needs of persons with ASDs and their families. Introduction Autism spectrum disorders (ASDs) are a group of developmental disabilities characterized byimpairments in social interaction and communication and by restricted, repetitive, and stereotyped patterns of behavior ( 1 ). Symptoms typically are apparent before age 3 years. Since the early 1990s,elevated public concern about continued reported increases in the number of children receiving servicesfor ASDs and reports of higher-than-expected ASD prevalence estimates have underscored the need for systematic public health monitoring of ASDs ( 2 ). Tracking the prevalence of ASDs over time poses  unique challenges because of the complex nature of these disorders, a lack of biologic markers for diagnosis, and changes in clinical definitions over time.In 2000, CDC established the Autism and Developmental Disabilities Monitoring (ADDM) Network tocollect data that would provide estimates of the prevalence of ASDs and other developmental disabilitiesin the United States ( 2 ). Initial reports from the ADDM Network provided ASD prevalence estimatesfrom six sites for the 2000 surveillance year ( 3 ) and from 14 sites for the 2002 surveillance year ( 4 ).Estimates of ASD prevalence among children aged 8 years were similar for both surveillance years. Datacombined from all sites in each respective surveillance year yielded overall ASD prevalence estimates of 6.7 per 1,000 children aged 8 years in 2000 (range: 4.5–9.9) and 6.6 per 1,000 in 2002 (range: 3.3–10.6),or one in every 150 children aged 8 years.The subsequent ADDM Network report provided data on estimated ASD prevalence among children aged8 years for 2004 (eight sites) and 2006 (11 sites) ( 5 ). When data from all sites were combined, overallestimated ASD prevalence was 8.0 per 1,000 children aged 8 years in 2004 (range: 4.6–9.8), or one inevery 125 children, and 9.0 per 1,000 in 2006 (range: 4.2–12.1), or one in every 110 children aged 8years. ASD prevalence estimates for the 2002 and 2006 surveillance years were compared ( 5 ). All 10ADDM sites that provided data for both surveillance years reported an increase in estimated ASD prevalence (range: 27%–95%). By 2006, the combined estimated prevalence of ASDs in ADDM Network sites approached 1% of children aged 8 years, a 4-year increase of 57% among sites that provided datafor both the 2002 and 2006 surveillance years ( 5 ). Some of the increase in estimated ASD prevalencemight be attributed to improved identification, particularly among certain subgroups (e.g., childrenwithout intellectual disability and Hispanic children). These data indicated the importance of continuingto monitor trends in ASD prevalence and of accelerating the pace of research into risk factors andeffective interventions.Certain studies from the United States, Europe, and Asia have reported ASD prevalence estimates basedon national survey data, statewide administrative data, or community screening approaches ( 6–10 ).Results from these studies are generally consistent with those reported by the ADDM Network, althoughsome international prevalence estimates are higher. In the United States, parent-reported data from the2007 National Survey of Children's Health indicated an overall estimated prevalence of 11.0 per 1,000children aged 3–17 years ( 6  ), and data from the National Health Interview Survey demonstrated a nearlyfourfold increase in estimated ASD prevalence between the 1997–1999 and the 2006–2008 surveillance periods ( 7  ). A British study that employed both a questionnaire and direct screening methods estimated anASD prevalence of close to 1% of children aged 5–9 years during the 2003 and 2004 school years ( 8,9 ).A recent study based on population screening and direct assessment in South Korea estimated overallASD prevalence of 26.4 per 1,000 children aged 7–12 years in 2006 ( 10 ).This report provides updated ASD prevalence estimates from the ADDM Network for the 2008surveillance year, representing 14 sites in the United States. In addition to prevalence estimates,characteristics of the population of children with ASDs are described. This report is intended tocommunicate the latest available ASD prevalence estimates from the ADDM Network and to provide basic comparisons with estimates for earlier ADDM surveillance years. More focused efforts areunderway to analyze available data on multiple factors influencing the identification of children withASDs and potential changes in risk factors over time. Methods Study Sites The Children's Health Act of 2000 ( 11 ) authorized CDC to create the ADDM Network, the only  collaborative network to estimate the prevalence of ASDs in the United States. ADDM has multiplegoals: 1) to obtain as complete a count as possible of the number of children with ASDs in each projectarea, 2) to report comparable population-based ASD prevalence estimates from different sites anddetermine if these rates are changing over time, 3) to study whether autism is more common among somegroups of children than among others, and 4) to provide descriptive data on the population of childrenwith ASDs. Since the ADDM Network's inception in 2000, CDC has funded grantees in 14 states(Alabama, Arizona, Arkansas, Colorado, Florida, Maryland, Missouri, New Jersey, North Carolina,Pennsylvania, South Carolina, Utah, West Virginia, and Wisconsin). The ADDM Network implements amultisite, multiple-source, records-based surveillance methodology based on a model srcinallyimplemented by CDC's Metropolitan Atlanta Developmental Disabilities Surveillance Program(MADDSP) ( 12 ). The case definition and surveillance methods, which have been described in detail previously ( 2– 5 ,12,13 ), have remained consistent over time, enabling comparisons across multiplesurveillance years. ADDM focuses on children aged 8 years because a baseline ASD prevalence studyconducted by MADDSP demonstrated that this is the age of identified peak prevalence ( 12 ). MADDSPrepresents one ADDM site in Georgia, and the remaining ADDM projects are administered through statehealth departments or through universities working on behalf of their state health departments to collector receive information used for protecting public health. Sites were selected through a competitiveobjective review process on the basis of their ability to conduct active, records-based surveillance of ASDs; they were not selected to be a nationally representative sample. Each ADDM site participating inthe 2008 surveillance year functioned as a public health authority under the HIPAA Privacy Rule and metapplicable local Institutional Review Board and privacy/confidentiality requirements under 45 CFR 46( 14 ). Case Ascertainment ADDM is an active surveillance system that does not rely on professional or family reporting of anexisting diagnosis or classification to ascertain ASD case status. Case determination is completed in two phases. The first phase involves screening and abstraction of records at multiple data sources in thecommunity. All abstracted evaluations then are compiled and reviewed by trained clinicians to determineASD case status in the second phase of the study. In the first phase, a broad net is cast to screenthousands of records and identify a subset of children with general symptoms of ASDs, whereas a muchmore strict case definition is applied during the second phase of the study. Because children's records arescreened at multiple data sources, developmental assessments completed by a wide range of health andeducation providers are included. Data sources are categorized as either 1) education source type,including evaluations to determine eligibility for special education services or 2) health source type,including diagnostic and developmental assessments from psychologists, neurologists, developmental pediatricians, physical therapists, occupational therapists, speech/language pathologists, and other  providers. Agreements to access records are made at the institutional level in the form of contracts,memoranda, or other formal agreements. All ADDM Network sites have agreements in place to accessrecords at health sources; however, four ADDM sites (Alabama, Florida, Missouri, and Wisconsin) havenot been granted access to records at education sources, and in one site (Colorado), parents are notifieddirectly about the study and may request that their children's education records be excluded.In the first phase of the study, ADDM Network sites identify source records to review based on a child'syear of birth and either 1) eligibility classifications in special education or 2) International Classificationof Diseases, Ninth Revision (ICD-9) billing codes (Box) for select childhood disabilities or psychologicalconditions. Children's records are screened to confirm year of birth and residency in the surveillance areaat some time during the surveillance year. For children meeting age and residency requirements, thesource files are screened for certain behavioral or diagnostic descriptions defined by ADDM as triggers for abstraction (e.g., child does not initiate interactions with others, prefers to play alone or engage in
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