Autism epidemiology and demographics
|
Autism Microchapters |
|
Diagnosis |
|---|
|
Treatment |
|
Case Studies |
|
Autism epidemiology and demographics On the Web |
|
American Roentgen Ray Society Images of Autism epidemiology and demographics |
|
Risk calculators and risk factors for Autism epidemiology and demographics |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Most recent reviews estimate a prevalence of 100- 200 cases per 100,000 people for autism, and about 600 per 100,000 for ASD, with ASD averaging a 4.3:1 male-to-female ratio. The number of people known to have autism has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved.
Epidemiology and Demographics
Prevalence
Most recent reviews tend to estimate a prevalence of 100– 200 per 100,000 for autism and close to 600 per 100,000 for ASD;[1] because of inadequate data, these numbers may underestimate ASD's true prevalence.[2] PDD-NOS is the vast majority of ASD, Asperger's is about 30 per 100,000 and the remaining ASD forms are much rarer.[3] A 2006 study of nearly 57,000 British nine- and ten-year-olds reported a prevalence of 389 per 100,000 for autism and 1,161 per 100,000 for ASD; these higher figures could be associated with broadening diagnostic criteria.[4] Studies based on more-detailed information, such as direct observation rather than examination of medical records, identify higher prevalence; this suggests that published figures may underestimate ASD's true prevalence.[2]
Changes with Time
Attention has been focused on whether the prevalence of autism is increasing with time. Earlier prevalence estimates were lower, centering at about 50 per 100,000 for autism during the 1960s and 1970s and about 100 per 100,000 in the 1980s, as opposed to today's 100- 200 per 100,000.[1]
The number of reported cases of autism increased dramatically in the 1990s and early 2000s, prompting investigations into several potential reasons:[5]
- More children may have autism; that is, the true frequency of autism may have increased.
- There may be more complete pickup of autism (case finding), as a result of increased awareness and funding. For example, attempts to sue vaccine companies may have increased case-reporting.
- The diagnosis may be applied more broadly than before, as a result of the changing definition of the disorder, particularly changes in DSM-III-R and DSM-IV.
- Successively earlier diagnosis in each succeeding cohort of children, including recognition in nursery (preschool), may have affected apparent prevalence but not incidence.
The reported increase is largely attributable to changes in diagnostic practices, referral patterns, availability of services, age at diagnosis, and public awareness.[1][6][7] A widely cited 2002 pilot study concluded that the observed increase in autism in California cannot be explained by changes in diagnostic criteria,[8] but a 2006 analysis found that special education data poorly measured prevalence because so many cases were undiagnosed, and that the 1994–2003 U.S. increase was associated with declines in other diagnostic categories, indicating that diagnostic substitution had occurred.[9] A 2007 study that modeled autism incidence found that broadened diagnostic criteria, diagnosis at a younger age, and improved efficiency of case ascertainment, can produce an increase in the frequency of autism ranging up to 29-fold depending on the frequency measure, suggesting that methodological factors may explain the observed increases in autism over time.[10] A small 2008 study found that a significant number of people diagnosed with language impairments as children in previous decades would now be given a diagnosis as autism.[11]
Several contributing environmental risk factors have been proposed to support the hypothesis that the actual frequency of autism has increased. These include certain foods, infectious disease, pesticides, MMR vaccine, and vaccines containing the preservative thiomersal, formerly used in several childhood vaccines in the U.S.[1] Although there is overwhelming scientific evidence against the MMR hypothesis and no convincing evidence for the thiomersal hypothesis, other as-yet-unidentified contributing environmental risk factors cannot be ruled out.[6] Although it is unknown whether autism's frequency has increased, any such increase would suggest directing more attention and funding toward changing environmental factors instead of continuing to focus on genetics.[12]
References
- ↑ 1.0 1.1 1.2 1.3 Newschaffer CJ, Croen LA, Daniels J; et al. (2007). "The epidemiology of autism spectrum disorders". Annu Rev Public Health. 28: 235–58. doi:10.1146/annurev.publhealth.28.021406.144007. PMID 17367287.
- ↑ 2.0 2.1 Caronna EB, Milunsky JM, Tager-Flusberg H (2008). "Autism spectrum disorders: clinical and research frontiers". Arch Dis Child. 93 (6): 518–23. doi:10.1136/adc.2006.115337. PMID 18305076.
- ↑ Fombonne E (2005). "Epidemiology of autistic disorder and other pervasive developmental disorders". J Clin Psychiatry. 66 (Suppl 10): 3–8. PMID 16401144.
- ↑ Baird G, Simonoff E, Pickles A; et al. (2006). "Prevalence of disorders of the autism spectrum in a population cohort of children in South Thames: the Special Needs and Autism Project (SNAP)". Lancet. 368 (9531): 210–5. doi:10.1016/S0140-6736(06)69041-7. PMID 16844490.
- ↑ Wing L, Potter D (1999). "Notes on the prevalence of autism spectrum disorders". National Autistic Society. Retrieved 2007-12-10.
- ↑ 6.0 6.1 Rutter M (2005). "Incidence of autism spectrum disorders: changes over time and their meaning". Acta Paediatr. 94 (1): 2–15. PMID 15858952.
- ↑ Prevalence and changes in diagnostic practice:
- Fombonne E (2003). "The prevalence of autism". JAMA. 289 (1): 87–9. doi:10.1001/jama.289.1.87. PMID 12503982.
- Wing L, Potter D (2002). "The epidemiology of autistic spectrum disorders: is the prevalence rising?". Ment Retard Dev Disabil Res Rev. 8 (3): 151–61. doi:10.1002/mrdd.10029. PMID 12216059.
- ↑ Template:Cite paper
- ↑ Shattuck PT (2006). "The contribution of diagnostic substitution to the growing administrative prevalence of autism in US special education". Pediatrics. 117 (4): 1028–37. doi:10.1542/peds.2005-1516. PMID 16585296. Lay summary (2006-04-03).
- ↑ Wazana A, Bresnahan M, Kline J (2007). "The autism epidemic: fact or artifact?". J Am Acad Child Adolesc Psychiatry. 46 (6): 721–30. doi:10.1097/chi.0b013e31804a7f3b. PMID 17513984.
- ↑ Bishop DVM, Whitehouse AJO, Watt HJ, Line EA (2008). "Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder". Dev Med Child Neurol. 50 (5): 341–5. doi:10.1111/j.1469-8749.2008.02057.x. PMID 18384386.
- ↑ Szpir M (2006). "Tracing the origins of autism: a spectrum of new studies". Environ Health Perspect. 114 (7): A412–8. PMID 16835042.