Friday, December 18, 2009

NEWS: December 18 CDC Report finds increased autism prevalence from 2002 to 2006


**Update 7:30PM PST to add popular press articles on the story**
CDC Finds About 1 Percent Of Kids Have Autism
By Jon Hamilton, National Public Radio (NPR)
December 18, 2009 4:04 p.m. EST

Study: 1 in 110 U.S. children had autism in 2006
By Miriam Falco, CNN Medical News
December 18, 2009 4:39 p.m. EST
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A significant report from the December 18, 2009 Mortality and Morbidity Weekly Report volume 58, No. SS-10, prepared by the U.S. Centers for Disease Control and Prevention (CDC), reports that data from the Autism and Developmental Disabilities Monitoring (ADDM) Network shows an increased prevalence of ASD diagnosis in the 8-year olds sampled in 2006 compared to the previous survey of 2002 which was reported in the MMWR of February 9, 2007.

Article:
Prevalence of Autism Spectrum Disorders-Autism and Developmental Disabilities Monitoring Network, United States, 2006. Morbidity and Mortality Weekly Report; December 18, 2009; 58 (SS-10). CDC. [pdf version]

Abstract
Problem/Condition:
Autism spectrum disorders (ASDs) are a group of developmental disabilities characterized by atypical development in socialization, communication, and behavior. ASDs typically are apparent before age 3 years, with associated impairments affecting multiple areas of a person’s life. Because no biologic marker exists for ASDs, identification is made by professionals who evaluate a child’s developmental progress to identify the presence of developmental disorders.Reporting Period: 2006.

Methods:
Earlier surveillance efforts indicated that age 8 years is a reasonable index age at which to monitor peak prevalence. The identified prevalence of ASDs in U.S. children aged 8 years was estimated through a systematic retrospective review of evaluation records in multiple sites participating in the Autism and Developmental Disabilities Monitoring (ADDM) Network.

Data were collected from existing records in 11 ADDM Network sites (areas of Alabama, Arizona, Colorado, Florida, Georgia, Maryland, Missouri, North Carolina, Pennsylvania, South Carolina, and Wisconsin) for 2006. To analyze changes in identified ASD prevalence, CDC compared the 2006 data with data collected from 10 sites (all sites noted above except Florida) in 2002. Children aged 8 years with a notation of an ASD or descriptions consistent with an ASD were identified through screening and abstraction of existing health and education records containing professional assessments of the child’s developmental progress at health-care or education facilities. Children aged 8 years whose parent(s) or legal guardian(s) resided in the respective areas in 2006 met the case definition for an ASD if their records documented behaviors consistent with the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, text revision (DSM-IV-TR) criteria for autistic disorder, pervasive developmental disorder–not otherwise specified (PDD NOS), or Asperger disorder. Presence of an identified ASD was determined through a review of data abstracted from developmental evaluation records by trained clinician reviewers.

Results:
For the 2006 surveillance year, 2,757 (0.9%) of 307,790 children aged 8 years residing in the 11 ADDM sites were identified as having an ASD, indicating an overall average prevalence of 9.0 per 1,000 population (95% confidence interval [CI] = 8.6–9.3). ASD prevalence per 1,000 children aged 8 years ranged from 4.2 in Florida to 12.1 in Arizona and Missouri, with prevalence for the majority of sites ranging between 7.6 and 10.4. For 2006, ASD prevalence was significantly lower in Florida (p<0.001) and Alabama (p<0.05) and higher in Arizona and Missouri (p<0.05) than in all other sites. The ratio of males to females ranged from 3.2:1 in Alabama to 7.6:1 in Florida. ASD prevalence varied by type of ascertainment source, with higher average prevalence in sites with access to health and education records (10.0) compared with sites with health records only (7.5). Although parental or professional concerns regarding development before age 36 months were noted in the evaluation records of the majority of children who were identified as having an ASD, the median age of earliest documented ASD diagnosis was much later (range: 41 months [Florida]–60 months [Colorado]). Of 10 sites that collected data for both the 2002 and 2006 surveillance years, nine observed an increase in ASD prevalence (range: 27%–95% increase; p<0.01), with increases among males in all sites and among females in four of 11 sites, and variation among other subgroups.

Interpretation:
In 2006, on average, approximately 1% or one child in every 110 in the 11 ADDM sites was classified as having an ASD (approximate range: 1:80–1:240 children [males: 1:70; females: 1:315]). The average prevalence of ASDs identified among children aged 8 years increased 57% in 10 sites from the 2002 to the 2006 ADDM surveillance year. Although improved ascertainment accounts for some of the prevalence increases documented in the ADDM sites, a true increase in the risk for children to develop ASD symptoms cannot be ruled out. On average, although delays in identification persisted, ASDs were being diagnosed by community professionals at earlier ages in 2006 than in 2002.

Public Health Actions:
These results indicate an increased prevalence of identified ASDs among U.S. children aged 8 years and underscore the need to regard ASDs as an urgent public health concern. Continued monitoring is needed to document and understand changes over time, including the multiple ascertainment and potential risk factors likely to be contributing. Research is needed to ascertain the factors that put certain persons at risk, and concerted efforts are essential to provide support for persons with ASDs, their families, and communities to improve long-term outcome.

Some interesting excerpts from the December 18, 2009 MMRW article,

page 7: 
"...In general, estimated ASD prevalence was lower in ADDM sites that relied solely on health sources to identify cases (mean: 7.5 per 1,000 population; CI = 7.0–7.9) compared with sites that also had access to education sources (mean: 10.2 per 1,000 population; CI = 9.7–10.7) (p<0.001). For sites that relied solely on health sources, identified ASD prevalence was significantly higher in Missouri (12.1) and significantly lower in Florida (4.2) (p<0.001). Among sites with access to education sources, identified ASD prevalence was significantly higher in Arizona (12.1) than in each of the other sites (p<0.05) whereas prevalence in Colorado (7.5) was significantly lower (p<0.05) than in Arizona (12.1), Georgia (10.2), and North Carolina (10.4). In sites with access to both health and education sources, the proportion of ASD cases identified exclusively from education sources ranged from 20% in North Carolina to 78% in Arizona..."
From Discussion, page 14: 
"...Children identified with an ASD in 2006 reflect a group with less co-occurring cognitive impairment than the population identified ≥20 years ago, when autism was conceptualized in a more severe and singular form compared with the spectrum of disorders identified today (2,34). In 2006, of all children with an ASD for whom testing documentation was available, 41% had cognitive impairment. When modern criteria are applied, children identified are less likely to test as having general cognitive impairments, and unusual learning profiles indicating scatter in cognitive skills rather than across-the-board cognitive delays might be more salient indicators of an ASD than intellectual impairment (35)..."
Under Limitations, page 17:
"...In addition, CDC is conducting a validation study comparing records-based to direct evaluation methods. Although the ADDM sites were not selected to be a nationally representative sample, the population included represents a substantial number of children, >300,000 (7.9%) of all children in the United States aged 8 years in 2006..."

Under Public Health Implications, page 18: 
"Whether identified ASD prevalence estimates will plateau or continue to increase is unknown. The ADDM cohorts in this report comprise children born in 1994 (for 2002 data) and 1998 (for 2006 data). Children born starting in the mid-to-late 1990s were particularly susceptible to the changing influence of the new DSM-IV criteria in 1994 and to increased autism awareness among the public and health professionals (2,3). The impact on estimated ASD prevalence of the broadening of diagnostic criteria and the increased awareness of ASDs might reach a high point and then diminish after a period of time. Therefore, evaluating the prevalence of ASDs among children born in this millennium using the same standard for evaluating the change in ASD symptoms over time is critical to understanding the current and changing population of children with ASDs. Of note, recent research indicates that the core social traits of autism are distributed in the population along a continuum (51); where the line is drawn between trait measures regarded as normal variance in behavior versus those labeled as impairment or disability might affect ASD prevalence estimates. The landscape of ASD diagnoses is likely to change with the introduction of the next version of the DSM expected in 2012. Efforts are needed to examine prevalence changes in other childhood conditions such as attention-deficit/hyperactivity disorder, asthma, and allergies to assess whether changes in ASD prevalence are occurring in isolation (52–54)...."
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For further information, references:

CDC Press Briefing on Autism Surveillance Summary
Rough unedited transcript and mp3
Friday December 18, 2009.

The current report:

The prior reports from 2007

The Autism and Developmental Disabilities Monitoring (ADDM) Network
Autism and Developmental Disabilities Monitoring (ADDM) Network Publications

Morbidity and Mortality Weekly Report (MMWR)

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