Evaluating Changes in the Prevalence of the Autism Spectrum Disorders (ASDs)

Autism spectrum disorders (ASDs) are estimated to occur among about one percent of children in the United States. This estimate is in line with estimates from other industrialized countries. However, the identified prevalence of ASDs has increased significantly in a short time period based on data from multiple studies including the U.S. Centers for Disease Control and Prevention's (CDC) Autism and Developmental Disabilities Monitoring (ADDM) Network. Whether increases in ASD prevalence are partly attributable to a true increase in the risk of developing ASD or solely to changes in community awareness and identification patterns is not known. It is clear that more children are identified with an ASD now than in the past and the impact on individuals, families, and communities is significant. However, disentangling the many potential reasons for ASD prevalence increases has been challenging. Understanding the relative contribution of multiple factors such as variation in study methods, changes in diagnostic and community identification, and potential changes in risk factors is an important priority for the ADDM Network and for CDC. This article summarizes the discussion from a workshop that was co-sponsored by CDC and Autism Speaks as a forum for sharing knowledge and opinions of a diverse range of stakeholders about changes in ASD prevalence. Panelists discussed recommendations for building on existing infrastructure and developing new initiatives to better understand ASD trends. The information, research, and opinions shared during this workshop add to the knowledge base about ASD prevalence in an effort to stimulate further work to understand the multiple reasons behind increasing ASD prevalence.

Short report: Improving record-review surveillance of young children with an autism spectrum disorder

INTRODUCTION

Records-based autism spectrum disorder surveillance developed at the Centers for Disease Control and Prevention has been extended to younger cohorts, although the utility of additional record sources has not been examined. We therefore conducted a pilot project to describe whether Centers for Disease Control and Prevention surveillance could identify younger children with an autism spectrum disorder evaluated as part of an ongoing screening study at Georgia State University.

METHODS

In all, 31 families of children who screened positive for autism spectrum disorder and received a clinical evaluation at Georgia State University agreed to participate in the project. Of these, 10 children lived inside the surveillance area and had records abstracted and reviewed for this project. Centers for Disease Control and Prevention surveillance results (i.e. autism spectrum disorder or non-autism spectrum disorder) were compared with Georgia State University evaluation results (i.e. autism spectrum disorder or non-autism spectrum disorder).

RESULTS

In all, 4 of the 10 children were diagnosed with an autism spectrum disorder after the Georgia State University evaluation. None of the 4 children with an autism spectrum disorder were identified by current Centers for Disease Control and Prevention surveillance methods but all 4 children were identified by Centers for Disease Control and Prevention surveillance methods when additional record sources were included (i.e. records from the statewide early intervention program and Georgia State University evaluation).

CONCLUSION

These findings suggest that partnering with early intervention programs and encouraging early autism spectrum disorder screening might improve autism spectrum disorder surveillance among young children.

Parent-reported prevalence of autism spectrum disorders in US-born children: an assessment of changes within birth cohorts from the 2003 to the 2007 National Survey of Children's Health

The prevalence of autism spectrum disorders (ASD) from the 2007 National Survey of Children's Health (NSCH) was twice the 2003 NSCH estimate for autism. From each NSCH, we selected children born in the US from 1990 to 2000. We estimated autism prevalence within each 1-year birth cohort to hold genetic and non-genetic prenatal factors constant. Prevalence differences across surveys thus reflect survey measurement changes and/or external identification effects. In 2003, parents were asked whether their child was ever diagnosed with autism. In 2007, parents were asked whether their child was ever diagnosed with an ASD and whether s/he currently had an ASD. For the 1997-2000 birth cohorts (children aged 3-6 years in 2003 and 7-10 years in 2007), relative increases between 2003 autism estimates and 2007 ASD estimates were 200-600 %. For the 1990-1996 birth cohorts (children aged 7-13 years in 2003) increases were lower; nonetheless, differences between 2003 estimates and 2007 "ever ASD" estimates were >100 % for 6 cohorts and differences between 2003 estimates and 2007 "current ASD" estimates were >80 % for 3 cohorts. The magnitude of most birth cohort-specific differences suggests continuing diagnosis of children in the community played a sizable role in the 2003-2007 ASD prevalence increase. While some increase was expected for 1997-2000 cohorts, because some children have later diagnoses coinciding with school entry, increases were also observed for children ages ≥ 7 years in 2003. Given past ASD subtype studies, the 2003 "autism" question might have missed a modest amount (≤ 33 %) of ASDs other than autistic disorder.

Medical expenditures attributable to cerebral palsy and intellectual disability among Medicaid-enrolled children

This study estimated medical expenditures attributable to cerebral palsy (CP) among children enrolled in Medicaid, stratified by the presence of co-occurring intellectual disability (ID), relative to children without CP or ID. The MarketScan(®) Medicaid Multi-State database was used to identify children with CP for 2003-2005 by using the International Classification of Diseases, Ninth Revision; Clinical Modification (ICD-9-CM) code 343.xx. Children with ID were identified for 2005 by using ICD-9-CM code 317.xx-319.xx. Children without CP or ID during the same period served as control subjects. Medical expenditures were estimated for case and control children for 2005. The difference between the average expenditures for children with and without CP was used as a proxy for attributable expenditures for the condition. The attributable expenditures of co-occurring ID were calculated similarly as the difference in average expenditures among children with CP with and without ID. A total of 9927 children with CP were identified. Among them, 2022 (20.3%) children had co-occurring ID recorded in medical claims. Children with CP but without ID incurred medical expenditures that were $15,047 higher than those of control children without CP or ID. By contrast, children with CP and co-occurring ID incurred costs that were $41,664 higher, compared with control children, and $26,617 more than children with CP but without ID. Administrative data from a large, multistate database demonstrated high medical expenditures for publicly insured children with CP. Expenditures approximately tripled for children with CP and co-occurring ID.

Association between parental nativity and autism spectrum disorder among US-born non-Hispanic white and Hispanic children, 2007 National Survey of Children's Health

BACKGROUND

Limited studies suggest the prevalence of autism spectrum disorders (ASD) varies by whether maternal and child birth country are discordant.

OBJECTIVE/HYPOTHESIS

We explored associations between ASD and maternal and paternal nativity in a sample of US-born non-Hispanic white (NHW, n = 37,265) and US-born Hispanic (n = 4,690) children in the 2007 National Survey of Children's Health (NSCH).

METHODS

We assessed ASD prevalence within race-ethnicity and parental nativity subgroups. Prevalence ratios (aPR), comparing each group to NHW children with 2 US-born parents, were adjusted for child age, sex, and receipt of care in a medical home. Estimates were weighted to reflect US noninstitutionalized children. Standard errors were adjusted to account for the complex sample design.

RESULTS

In NHW children with 2 US-born parents, ASD prevalence was 1.19%; estimates were similar for NHW children with a foreign-born mother or father. There was a striking heterogeneity between Hispanic children with 2 US-born versus 2 foreign-born parents (ASD prevalence 2.39% versus 0.31%, p = .05). Even after adjustment, PRs comparing ASD prevalence in Hispanic versus NHW children were vastly different for Hispanic subgroups, suggesting a substantially lower prevalence for Hispanic children with both parents foreign-born (aPR 0.2, 95% confidence interval 0.1-0.5) and a higher prevalence for Hispanic children with both parents US-born (aPR 2.0 [0.8-4.6]).

CONCLUSIONS

Previous studies comparing ASD prevalence between NHW and Hispanic children based on a composite Hispanic grouping without consideration of parental nativity likely missed important differences between these racial-ethnic groups. Continuing efforts toward improving early identification in Hispanic children are needed.

Effect of incorporating adaptive functioning scores on the prevalence of intellectual disability

Surveillance and epidemiologic research on intellectual disability often do not incorporate adaptive functioning (AF) data. Exclusion of AF data leads to overestimation of the prevalence of intellectual disability, the extent of which is not known. In this study, the authors evaluated the effect of incorporating AF data on overall intellectual disability prevalence according to sociodemographic, economic, and severity characteristics. Between 2002 and 2006, the Metropolitan Atlanta Developmental Disabilities Surveillance Program identified 1,595 8-year-old children who met the study's intellectual disability surveillance-case definition of IQ ≤ 70. AF scores were not available for 9.2% of the case children, specifically those with mild intellectual disability and low socioeconomic backgrounds. Prevalence estimates showed few substantive changes when incorporating AF data. The authors conclude that use of IQ data alone appears to be appropriate for measuring population intellectual disability prevalence.

Trends in the prevalence of developmental disabilities in US children, 1997-2008

OBJECTIVE

To fill gaps in crucial data needed for health and educational planning, we determined the prevalence of developmental disabilities in US children and in selected populations for a recent 12-year period.

PARTICIPANTS AND METHODS

We used data on children aged 3 to 17 years from the 1997-2008 National Health Interview Surveys, which are ongoing nationally representative samples of US households. Parent-reported diagnoses of the following were included: attention deficit hyperactivity disorder; intellectual disability; cerebral palsy; autism; seizures; stuttering or stammering; moderate to profound hearing loss; blindness; learning disorders; and/or other developmental delays.

RESULTS

Boys had a higher prevalence overall and for a number of select disabilities compared with girls. Hispanic children had the lowest prevalence for a number of disabilities compared with non-Hispanic white and black children. Low income and public health insurance were associated with a higher prevalence of many disabilities. Prevalence of any developmental disability increased from 12.84% to 15.04% over 12 years. Autism, attention deficit hyperactivity disorder, and other developmental delays increased, whereas hearing loss showed a significant decline. These trends were found in all of the sociodemographic subgroups, except for autism in non-Hispanic black children.

CONCLUSIONS

Developmental disabilities are common and were reported in ~1 in 6 children in the United States in 2006-2008. The number of children with select developmental disabilities (autism, attention deficit hyperactivity disorder, and other developmental delays) has increased, requiring more health and education services. Additional study of the influence of risk-factor shifts, changes in acceptance, and benefits of early services is needed.

Prevalence and functioning of children with cerebral palsy in four areas of the United States in 2006: a report from the Autism and Developmental Disabilities Monitoring Network

AIM

To estimate the prevalence of cerebral palsy (CP) and the frequency of co-occurring developmental disabilities (DDs), gross motor function (GMF), and walking ability using the largest surveillance DD database in the US.

METHODS

We conducted population-based surveillance of 8-year-old children in 2006 (N=142,338), in areas of Alabama, Georgia, Wisconsin, and Missouri. This multi-site collaboration involved retrospective record review at multiple sources. We reported CP subtype, co-occurring DDs, Gross Motor Function Classification System (GMFCS) level, and walking ability as well as CP period prevalence by race/ethnicity and sex.

RESULTS

CP prevalence was 3.3 (95% confidence interval [CI]: 3.1-3.7) per 1000 and varied by site, ranging from 2.9 (Wisconsin) to 3.8 (Georgia) per 1000, 8-year olds (p<0.02). Approximately 81% had spastic CP. Among children with CP, 8% had an autism spectrum disorder and 35% had epilepsy. Using the GMFCS, 38.1% functioned at the highest level (I), with 17.1% at the lowest level (V). Fifty-six percent were able to walk independently and 33% had limited or no walking ability.

INTERPRETATION

Surveillance data are enhanced when factors such as functioning and co-occurring conditions known to affect clinical service needs, quality of life, and health care are also considered.

Feasibility and reliability of classifying gross motor function among children with cerebral palsy using population-based record surveillance

For conditions with wide-ranging consequences, such as cerebral palsy (CP), population-based surveillance provides an estimate of the prevalence of case status but only the broadest understanding of the impact of the condition on children, families or society. Beyond case status, information regarding health, functional skills and participation is necessary to fully appreciate the consequences of the condition. The purpose of this study was to assess the feasibility and reliability of enhancing population-based surveillance by classifying gross motor function (GMF) from information available in medical records of children with CP. We assessed inter-rater reliability of two GMF classification methods, one the Gross Motor Function Classification System (GMFCS) and the other a 3-category classification of walking ability: (1) independently, (2) with handheld mobility device, or (3) limited or none. Two qualified clinicians independently reviewed abstracted evaluations from medical records of 8-year-old children residing in southeast Wisconsin, USA who were identified as having CP (n = 154) through the Centers for Disease Control and Prevention's Autism and Developmental Disabilities Monitoring Network. Ninety per cent (n = 138) of the children with CP had information in the record after age 4 years and 108 (70%) had adequate descriptions of gross motor skills to classify using the GMFCS. Agreement was achieved on 75.0% of the GMFCS ratings (simple kappa = 0.67, 95% confidence interval [95% CI 0.57, 0.78], weighted kappa = 0.83, [95% CI 0.77, 0.89]). Among case children for whom walking ability could be classified (n = 117), approximately half walked independently without devices and one-third had limited or no walking ability. Across walking ability categories, agreement was reached for 94% (simple kappa = 0.90, [95% CI 0.82, 0.96], weighted kappa = 0.94, [95% CI 0.89, 0.98]). Classifying GMF in the context of active records-based surveillance is feasible and reliable. Future surveillance efforts that include functional level among children with cerebral palsy may provide important information for monitoring the impact of the condition for programmatic and policy purposes.

Increased risk of death among children with Lennox-Gastaut syndrome and infantile spasms

The magnitude and causes of death among a cohort of children with epilepsy were determined. A follow-up study with a population-based cohort of 10-year-old children in the metropolitan Atlanta area with epilepsy was conducted. The National Death Index and linkage to State of Georgia death certificates were used to identify deaths. The authors estimated the expected numbers of deaths by applying mortality rates adjusted by age, race, and sex for the entire state of Georgia to the population for the follow-up period. Among the 688 children who were in the final epilepsy cohort, 64 deaths occurred; 20.6 deaths were expected (mortality ratio adjusted for age, race, and sex = 3.11). The mortality ratios for children with Lennox-Gastaut syndrome and infantile spasms were 13.92 and 11.91, respectively. Children and adolescents with epilepsy, especially those with Lennox-Gastaut syndrome or infantile spasms, have an increased risk of death.

Prevalence of developmental disabilities and receipt of special education services among children with an inborn error of metabolism

OBJECTIVE

To examine the presence of developmental disabilities and receipt of special education services in children with an inborn error of metabolism.

STUDY DESIGN

The study population was children born from 1988 through 2001 in whom a metabolic disorder was diagnosed after identification by newborn screening (n = 97) or after clinical identification (n = 34). These children were linked to the Metropolitan Atlanta Development Disability Surveillance Program (MADDSP) and Special Education Database of Metropolitan Atlanta (SEDMA) to determine developmental outcomes at 8 years of age and 3 through 10 years of age, respectively. Medical and educational records were examined to consider factors contributing to developmental outcomes.

RESULTS

Of 97 children with a metabolic disorder identified with newborn screening, 12 (12.4%) were identified by SEDMA as receiving special education services and 2 (2.7%) were identified by MADDSP as having a developmental disability. Of the 34 children with a clinically identified metabolic disorder, 8 (23.5%) were identified with SEDMA, and 5 (17.2%) were identified with a MADDSP developmental disability.

CONCLUSION

Early identification and treatment have been successful in limiting the impact of severe developmental disabilities. Continued surveillance and research are needed to monitor less severe developmental outcomes.

Changes in autism spectrum disorder prevalence in 4 areas of the United States

BACKGROUND

We sought to describe autism spectrum disorder (ASD) population characteristics and changes in identified prevalence across 3 time periods.

METHODS

Children with a potential ASD were identified through records abstraction at multiple sources with clinician review based on Diagnostic and Statistical Manual (DSM-IV-TR) criteria. Multisite, population-based data from the Autism and Developmental Disabilities Monitoring (ADDM) Network were analyzed from areas of Arizona (AZ), Georgia (GA), Maryland (MD), and South Carolina (SC). Participants were 8-year-old children (born in 1992, 1994, or 1996) in 2000, 2002, or 2004 (and children born in 1988 residing in metropolitan Atlanta in 1996) who had been evaluated for a variety of developmental concerns at education and/or health sources.

RESULTS

From 2000 to 2004, the identified prevalence of the ASDs per 1,000 8-year-old children showed significant increases of 38% in GA and 72% in MD and a nonsignificant increase of 26% in AZ. ASD prevalence was relatively stable in SC with a nonsignificant decrease of 17%. Males had a higher identified prevalence of ASD in all years. Increases among racial, ethnic, and cognitive functioning subgroups varied by site and surveillance year. More children were classified with an ASD by community professionals over time, except in AZ.

CONCLUSIONS

There was a trend toward increase in identified ASD prevalence among 8-year-old children who met the surveillance case definition in 3 of the 4 study sites from 2000 to 2004. Some of the observed increases are due to improved ascertainment; however, a true increase in ASD symptoms cannot be ruled out. These data confirm that the prevalence of ASDs is undergoing significant change in some areas of the United States and that ASDs continue to be of urgent public health concern.

A multi-dimensional approach to the transition of children with developmental disabilities into young adulthood: The acquisition of adult social roles

PURPOSE

To test the hypothesis that the difficulties young adults with developmental disabilities have in obtaining adult social roles are not inevitable consequences of their childhood impairment. We used the conceptual framework of the International Classification of Functioning, Disability, and Health to test this hypothesis.

METHOD

We used a structured questionnaire to obtain information on the consequences of childhood impairment in young adulthood and to examine the relationship between impairment and acquisition of adult social roles. The sample (n = 635) came from the Metropolitan Atlanta Developmental Disabilities Follow-up Study of Young Adults, a population-based cohort of young adults aged 21 - 25 years identified at age 10 with childhood impairment.

RESULTS

The results suggest that: (i) attaining adult social roles varies by impairment type and severity, (ii) experiencing activity limitations partially mediate the relationship between impairment and adult social roles, and (iii) attending postsecondary education increases the likelihood of attaining markers of adulthood.

CONCLUSIONS

Intervention to reduce activity limitations and to develop strategies to increase attendance in postsecondary education may increase the likelihood for the acquisition of adult social roles among young adults with childhood impairment.

Activity limitations among young adults with developmental disabilities: a population-based follow-up study

Developmental disabilities are a heterogeneous group of chronic conditions that may result in substantial activity limitations. The type and number of limitations may vary by impairment characteristics. Economic and social constraints may impact activity limitations beyond those attributable to their impairment. Using the International Classification of Functioning (ICF), Disability, and Health conceptual framework, this study tests the hypothesis that activity limitations in young adulthood are not inevitable consequences of childhood impairment. The Metropolitan Atlanta Developmental Disabilities Follow-up Study of Young Adults, a cohort of young adults ages 21-25, is used to examine the relationship between childhood impairment and activity limitations in young adulthood. For young adults with isolated impairment, activity limitations are not probable outcomes. This situation is not the case for those with severe intellectual disability and/or multiple impairments. The type and extent of activity limitations vary by impairment characteristics. With the goal of improving and preventing activity limitations in young adults with various types and severities of childhood impairment, additional research is needed to further identify areas for secondary and tertiary prevention of the consequences of childhood impairment. The conceptual framework of the ICF provides a useful tool for testing hypotheses to pinpoint areas of intervention.

Racial/ethnic disparities in the identification of children with autism spectrum disorders

OBJECTIVES

We sought to examine racial and ethnic disparities in the recognition of autism spectrum disorders (ASDs).

METHODS

Within a multisite network, 2568 children aged 8 years were identified as meeting surveillance criteria for ASD through abstraction of evaluation records from multiple sources. Through logistic regression with random effects for site, we estimated the association between race/ethnicity and documented ASD, adjusting for gender, IQ, birthweight, and maternal education.

RESULTS

Fifty-eight percent of children had a documented autism spectrum disorder. In adjusted analyses, children who were Black (odds ratio [OR] = 0.79; 95% confidence interval [CI] = 0.64, 0.96), Hispanic (OR = 0.76; CI = 0.56, 0.99), or of other race/ethnicity (OR = 0.65; CI = 0.43, 0.97) were less likely than were White children to have a documented ASD. This disparity persisted for Black children, regardless of IQ, and was concentrated for children of other ethnicities when IQ was lower than 70.

CONCLUSIONS

Significant racial/ethnic disparities exist in the recognition of ASD. For some children in some racial/ethnic groups, the presence of intellectual disability may affect professionals' further assessment of developmental delay. Our findings suggest the need for continued professional education related to the heterogeneity of the presentation of ASD.

Prevalence of cerebral palsy in 8-year-old children in three areas of the United States in 2002: a multisite collaboration

OBJECTIVE

The goal was to estimate the prevalence of cerebral palsy and cerebral palsy subtypes among children in 3 areas of the United States by using a population-based surveillance system.

METHODS

Using methods developed by the Centers for Disease Control and Prevention Metropolitan Atlanta Developmental Disabilities Surveillance Program, investigators from the Autism and Developmental Disabilities Monitoring Network conducted surveillance of cerebral palsy among 8-year-old children living in northern Alabama, metropolitan Atlanta, and southeastern Wisconsin in 2002 (N = 114,897). Cross-sectional data were collected through retrospective record review from multiple sources. Cases were linked to birth certificate and census files to obtain additional information. Period prevalence estimates were calculated per 1000 children 8 years of age.

RESULTS

The average prevalence of cerebral palsy across the 3 sites was 3.6 cases per 1000, with notably similar site-specific prevalence estimates (3.3 cases per 1000 in Wisconsin, 3.7 cases per 1000 in Alabama, and 3.8 cases per 1000 in Georgia). At all sites, prevalence was higher in boys than girls (overall boy/girl ratio: 1.4:1). Also, at all sites, the prevalence of cerebral palsy was highest in black non-Hispanic children and lowest in Hispanic children. At all sites, the prevalence among children living in low- and middle-income neighborhoods was higher than that among children living in high-income neighborhoods. Spastic cerebral palsy was the most common subtype (77% of all cases), with bilateral spastic cerebral palsy dominating the spastic group (70%).

CONCLUSION

These findings contribute new knowledge to the epidemiology of cerebral palsy in the United States. The similarities in prevalence rates and patterns of cerebral palsy reported for 8-year-old children at 3 geographically distinct sites provide evidence of the reliability of the surveillance methods used by the Autism and Developmental Disabilities Monitoring Network.

Factors associated with leisure activity among young adults with developmental disabilities

The framework of the International Classification of Functioning, Disability, and Health (ICF) was applied to examine the factors associated with childhood impairment and leisure activity. Information on leisure activity was obtained using a structured questionnaire from a population-based cohort of young adults with childhood impairment. The results underscore the differences in leisure lifestyles by impairment type and severity. Activity limitations, educational attainment, and the acquisition of adult social roles were significant predictors of leisure activity. This study emphasizes the importance of improving daily activities, increasing attendance of postsecondary school and opportunities for competitive employment and participation in impairment-related programs to help increase the number and scope of types of leisure activities for young adults with developmental disabilities.

Healthy behaviors and lifestyles in young adults with a history of developmental disabilities

OBJECTIVE

Measure select Healthy People 2010 Leading Health Indicators in young adults with and without a history of developmental disabilities (DD) using a population-based cohort.

METHODS

Young adults were interviewed to assess the prevalence of seven Leading Health Indicators: physical activity, overweight and obesity, tobacco use, substance abuse, responsible sexual behavior, injury and violence, and access to healthcare.

RESULTS

Young adults with a history of DD were less likely to be involved in tobacco use, substance abuse and sexual activity. Areas of concern included below normal Body Mass Index, lack of HIV/AIDS and sex education, preventive healthcare services for women, and victimization.

CONCLUSIONS

Despite some healthy lifestyle indicators, health gaps may place young adults with a history of DD at risk for poor health and quality of life.