Autism epidemiology and demographics: Difference between revisions
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===Prevalence=== | ===Prevalence=== | ||
[[Image:US-autism-6-11-1996-2005.png|thumb|left|Reports of autism cases grew dramatically in the U.S. in 1996–2005. It is unknown how much, if any, growth came from changes in autism's [[prevalence]].]] | [[Image:US-autism-6-11-1996-2005.png|thumb|left|Reports of autism cases grew dramatically in the U.S. in 1996–2005. It is unknown how much, if any, growth came from changes in autism's [[prevalence]].]] | ||
Most recent [[review]]s tend to estimate a prevalence of 100– 200 per 100,000 for autism and close to 600 per 100,000 for ASD;<ref name=Newschaffer>{{cite journal |author= Newschaffer CJ, Croen LA, Daniels J ''et al.'' |title= The epidemiology of autism spectrum disorders |journal= Annu Rev Public Health |year=2007 |volume=28 |pages=235–58 |pmid=17367287 |doi=10.1146/annurev.publhealth.28.021406.144007}}</ref> because of inadequate data, these numbers may underestimate ASD's true prevalence.<ref name=Caronna>{{cite journal |journal= Arch Dis Child |date=2008 |volume=93 |issue=6 |pages=518–23 |title= Autism spectrum disorders: clinical and research frontiers |author= Caronna EB, Milunsky JM, Tager-Flusberg H |doi=10.1136/adc.2006.115337 |pmid=18305076}}</ref> [[PDD-NOS]] is the vast majority of ASD, [[Asperger's]] is about 30 per 100,000 and the remaining ASD forms are much rarer.<ref>{{cite journal |journal= J Clin Psychiatry |date=2005 |volume=66 |issue=Suppl 10 |pages=3–8 |title= Epidemiology of autistic disorder and other pervasive developmental disorders |author= [[Eric Fombonne|Fombonne E]] |pmid=16401144}}</ref> The number of reported cases of autism increased dramatically in the 1990s and early 2000s. | Most recent [[review]]s tend to estimate a prevalence of 100– 200 per 100,000 for autism and close to 600 per 100,000 for ASD;<ref name=Newschaffer>{{cite journal |author= Newschaffer CJ, Croen LA, Daniels J ''et al.'' |title= The epidemiology of autism spectrum disorders |journal= Annu Rev Public Health |year=2007 |volume=28 |pages=235–58 |pmid=17367287 |doi=10.1146/annurev.publhealth.28.021406.144007}}</ref> because of inadequate data, these numbers may underestimate ASD's true prevalence.<ref name=Caronna>{{cite journal |journal= Arch Dis Child |date=2008 |volume=93 |issue=6 |pages=518–23 |title= Autism spectrum disorders: clinical and research frontiers |author= Caronna EB, Milunsky JM, Tager-Flusberg H |doi=10.1136/adc.2006.115337 |pmid=18305076}}</ref> [[PDD-NOS]] is the vast majority of ASD, [[Asperger's]] is about 30 per 100,000 and the remaining ASD forms are much rarer.<ref>{{cite journal |journal= J Clin Psychiatry |date=2005 |volume=66 |issue=Suppl 10 |pages=3–8 |title= Epidemiology of autistic disorder and other pervasive developmental disorders |author= [[Eric Fombonne|Fombonne E]] |pmid=16401144}}</ref> 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.<ref>{{cite journal |title= Prevalence of disorders of the autism spectrum in a population cohort of children in South Thames: the Special Needs and Autism Project (SNAP)|author=Baird G, Simonoff E, Pickles A ''et al.'' |journal=Lancet |volume=368 |issue=9531 |pages=210–5 |date=2006 |pmid=16844490 |doi=10.1016/S0140-6736(06)69041-7}}</ref> 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.<ref name=Caronna>{{cite journal |journal= Arch Dis Child |date=2008 |volume=93 |issue=6 |pages=518–23 |title= Autism spectrum disorders: clinical and research frontiers |author= Caronna EB, Milunsky JM, Tager-Flusberg H |doi=10.1136/adc.2006.115337 |pmid=18305076}}</ref> | ||
*{{cite journal|author=Fombonne E|title=The prevalence of autism|journal=JAMA|date=2003|volume=289|issue=1|pages=87–9|pmid=12503982}} | ====Changes with Time==== | ||
*{{cite journal|author=Wing L, Potter D|title=The epidemiology of autistic spectrum disorders: is the prevalence rising?|journal=Ment Retard Dev Disabil Res Rev|volume=8|issue=3|year=2002|pages=151–61|pmid=12216059|doi=10.1002/mrdd.10029}}</ref> | 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.<ref name=Newschaffer/> | ||
[[Image:US-autism-6-11-1996-2005.png|thumb|left|Reports of autism cases grew dramatically in the U.S. in 1996–2005. It is unknown how much, if any, growth came from changes in autism's [[prevalence]].<ref name=Prevalence/>]] | |||
The number of reported cases of autism increased dramatically in the 1990s and early 2000s, prompting investigations into several potential reasons:<ref>{{cite web |url=http://www.nas.org.uk/nas/jsp/polopoly.jsp?d=364&a=2618 |title= Notes on the prevalence of autism spectrum disorders |author= [[Lorna Wing|Wing L]], Potter D |publisher= National Autistic Society |date=1999 |accessdate=2007-12-10}}</ref> | |||
* 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.<ref name=Newschaffer/><ref name=Rutter/><ref name=Prevalence>Prevalence and changes in diagnostic practice: | |||
*{{cite journal |author=Fombonne E |title= The prevalence of autism |journal=JAMA |date=2003 |volume=289 |issue=1 |pages=87–9 |pmid=12503982 |doi= 10.1001/jama.289.1.87}} | |||
*{{cite journal |author=Wing L, Potter D |title= The epidemiology of autistic spectrum disorders: is the prevalence rising? |journal= Ment Retard Dev Disabil Res Rev |volume=8 |issue=3 |year=2002 |pages=151–61 |pmid=12216059 |doi=10.1002/mrdd.10029}}</ref> A widely cited 2002 pilot study concluded that the observed increase in autism in California cannot be explained by changes in diagnostic criteria,<ref>{{cite paper |author= Byrd RS, Sage AC, Keyzer J ''et al.'' |publisher=[[M.I.N.D. Institute]] |title= Report to the legislature on the principal findings of the epidemiology of autism in California: a comprehensive pilot study |date=2002 |url=http://www.ucdmc.ucdavis.edu/mindinstitute/newsroom/study_final.pdf |accessdate=2006-09-18 |format=PDF}}</ref> 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.<ref name=Shattuck>{{cite journal |journal=Pediatrics |date=2006 |volume=117 |issue=4 |pages=1028–37 |title= The contribution of diagnostic substitution to the growing administrative prevalence of autism in US special education |author= Shattuck PT |doi=10.1542/peds.2005-1516 |pmid=16585296 |url=http://pediatrics.aappublications.org/cgi/content/full/117/4/1028 |laysummary=http://www.news.wisc.edu/12368 |laydate=2006-04-03}}</ref> 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.<ref>{{cite journal |journal= J Am Acad Child Adolesc Psychiatry |date=2007 |volume=46 |issue=6 |pages=721–30 |title= The autism epidemic: fact or artifact? |author= Wazana A, Bresnahan M, Kline J |pmid=17513984 |doi= 10.1097/chi.0b013e31804a7f3b}}</ref> 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.<ref>{{cite journal |journal= Dev Med Child Neurol |date=2008 |volume=50 |issue=5 |pages=341–5 |title= Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder |author= Bishop DVM, Whitehouse AJO, Watt HJ, Line EA |doi=10.1111/j.1469-8749.2008.02057.x |pmid=18384386}}</ref> | |||
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 controversy|MMR vaccine]], and vaccines containing the preservative [[Thiomersal controversy|thiomersal]], formerly used in several childhood vaccines in the U.S.<ref name=Newschaffer/> 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.<ref name=Rutter>{{cite journal |author= [[Professor Sir Michael Rutter|Rutter M]] |title= Incidence of autism spectrum disorders: changes over time and their meaning |journal= Acta Paediatr |volume=94 |issue=1 |date=2005 |pages=2–15 |pmid=15858952}}</ref> 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.<ref>{{cite journal |journal= Environ Health Perspect |date=2006 |volume=114 |issue=7 |pages=A412–8 |title= Tracing the origins of autism: a spectrum of new studies |author= Szpir M |url=http://www.ehponline.org/members/2006/114-7/focus.html |pmid=16835042}}</ref> | |||
==References== | ==References== | ||
Revision as of 22:46, 10 February 2013
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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:[6]
- 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][7][5] 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.[7] 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.
- ↑ 5.0 5.1 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.
- ↑ Wing L, Potter D (1999). "Notes on the prevalence of autism spectrum disorders". National Autistic Society. Retrieved 2007-12-10.
- ↑ 7.0 7.1 Rutter M (2005). "Incidence of autism spectrum disorders: changes over time and their meaning". Acta Paediatr. 94 (1): 2–15. PMID 15858952.
- ↑ 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.