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EspañolAUTISM (INCIDENCE)
:''See Autism for general information about autism. See Incidence (epidemiology) for information about incidence.''
The reported 'incidence of autism' varies considerably among countries and is complicated by varying criteria for diagnosing autism, different standards for reporting public health problems, and other possible variations.
Autism was first characterised in 1943 by psychiatrist Dr. Leo Kanner of the Johns Hopkins Hospital in Baltimore, and almost simultaneously, in German, by Dr Hans Asperger. Both published case series of children with strikingly similar features.
The number of children born in each year diagnosed with autism in countries reporting figures is larger now than then. The populations of those countries have also increased but it is unclear what change in the incidence fraction has occurred. Public health organizations and researchers are not yet confident they have completely determined causes for all changes in the rate of reports of Autism (''vide infra''). Potential factors listed by the UK National Autistic Society include:[1]
★ The underlying condition may have a changing incidence with time, i.e., more children (and/or more per thousand born) are affected by it;
★ More complete pickup of autism (case finding), as a result of increased awareness and funding;
;
★ Attempts in the US and UK to sue vaccine companies may have also increased case-reporting.
★ The diagnosis being applied more broadly than before, as a result of the changing definition of the disorder, particularly changes in DSM-III-R;[2] and DSM-IV [3]
★ Successively earlier diagnosis in each succeeding cohort of children including recognition in nursery (preschool) - this would affect apparent prevalence but not incidence
The 'incidence' of a condition is the rate at which new cases occur in a population during a specified interval, e.g. "10 per year" or "12 in 1982". The 'prevalence' of a condition is the proportion of a population that are cases at a point in time, e.g. "1 in 1000". [4]
Examples of the way information is collected to specifically measure incidence rather than prevalence include:
★ Annual and age specific incidence for first recorded diagnoses of autism (that is, when the diagnosis of autism was first recorded);
★ Annual, birth cohort specific risk of autism diagnosed[5]
When the rising prevalence of autism spectrum disorders sparked research in the late 1990s, medical opinion initially attributed the increase to improved diagnostic screening or changes in the definition of autism. In 1994, the fourth major revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) was published[6] with updated criteria for the diagnosis of autism and autism spectrum disorders.[7] Professional medical associations, including the American Academy of Pediatrics, say that this revision was an important factor in increasing the apparent prevalence of autism and a 2005 study by Mayo Clinic researchers found increases in autism diagnoses followed the revisions in DSM criteria and changes in funding for special education programs.[8]
An increased awareness of autistic disorders by parents and pediatricians may have also led to increased reporting of Autism due to 'case substitution', which occurs when children with other disorders are identified as autistic.[9] This misdiagnosis may occur for several reasons including an increase in government funding for care of children diagnosed as autistic, but not for children with a similar degree of disability and need . If this is occurring, it means that children who in the past would probably have been diagnosed as having a different condition, or not diagnosed at all are recorded as new cases of autistic spectrum disorder. Possible alternate diagnoses include mental retardation, learning disability and childhood schizophrenia [10]. High-functioning autistic children are sometimes misdiagnosed ADHD.
[11] Children who are not primarily autistic, e.g. those with Fragile-X Syndrome (with characteristics that fit the criteria for autism) and even Down's Syndrome may have the diagnostic group with the best funding assigned.[12]
There have been suggestions that the incidence of autism may vary amongst particular groups defined by occupation, lifestyle or genetic isolation. Changes that made travel and communication easier, and the growth of the technological industries during the past decade, have been suggested as means for increase in the proportion of couples likely to produce an autistic child. None of these have been established.[13] [14]
[15][16]
The Yokohama study in Japan (2005) examined the incidence of autism before and after the 1993 withdrawal of MMR, reporting 48 and 86 cases per 10,000 children in two sequential years before withdrawal, doubling to 97 and 161 per 10,000 afterwards in the two years afterwards.[17][18]
It studied over 30,000 children (278 cases) born in one district of Yokohama.[19]
The National Autistic Society regarded the incidence and changes in incidence with time as unclear.[20] A 2001 review,[21] by the Medical Research Council, yielded an estimate of one in 166 in children under eight.
The reported autism incidence in the UK rose starting before the first introduction of the MMR vaccine in 1989.[5]
After years of substantial annual increases, provisional data from the US Department of Education show a significant decrease in the number of new autism diagnoses recorded among children 3 to 5 years old. There were 1,451 new cases in 2001-2002; 1,981 in 2002-2003; 3,707 in 2003-2004; and 3,178 in 2004-2005, a drop of 529 new cases, or 14%.[23]
The incidence of autism increased by over 900% between 1992 and 2001, according to the United States Department of Education. In 1999, the autism incidence rate in the US was generally cited at 4.5 cases per 10,000 live births. By 2005, the US Centers for Disease Control (CDC) estimated one of every 250 babies was born with autism, or 4 cases per 1000.
"The incidence of research-identified autism increased in Olmsted County from 1976 to 1997, with the increase occurring among young children after the introduction of broader, more precise diagnostic criteria, increased availability of services, and increased awareness of autism." The authors ascribed this to "improved awareness, changes in diagnostic criteria, and availability of services, leading to identification of previously unrecognized young children with autism." [25]
In November 2002, a study reported a lower incidence of autism in Denmark than in the US and other countries. An incidence of 1 in 727 (738 out of 537,303) was reported, compared with up to 1 in 86 among primary school children in the United Kingdom and around 1 in 150 children in the USA. Danish authorities also reported a continued increase in the incidence of autism after 1992 after withdrawal of thiomersal-containing vaccines.[26] Data presented in 2003 shows a clear increase in incidence between 1990 and 1995 (before the criteria changed). Thus, the increased incidence of autism after the removal of thiomersal was not a measurement artefact,[27] nevertheless Dan Olmsted argued that this was an artefact due to a change in criteria for registration of children with autism in Denmark.[28]
1. 2618 Incidence National Autistic Society
2. [http://ajp.psychiatryonline.org/cgi/content/abstract/145/11/1404 DSM3 changes
3. DSM4 changes
4. British Medical Journal: Epidemiology for the Uninitiated 4th Ed: Quantifying diseases in populations BMJ
5. Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend analysis, Kaye JA, del Mar Melero-Montes M, Jick H, , , BMJ, 2001
6. [1]
7. [2]
8. The incidence of autism in Olmsted County, Minnesota, 1976-1997: results from a population-based study, Barbaresi WJ, Katusic SK, Colligan RC, Weaver AL, Jacobsen SJ, , , Archives of pediatrics & adolescent medicine, 2005
9. Am. Assoc. paed. Case substitution accounts for some of the increase in reported incidence
10. [3]
11. [4]
12. CNN report Dr Fred Volkmar, an autism researcher from Yale said "Autism is a kind of fashionable diagnosis".
13. Parental type
14. BBC report Simon Baron-Cohen believes that "it has become easier for systemizers to meet each other, with the advent of international conferences, greater job opportunities and more women working in these fields."
15. [5] Assortative mating has not been demonstrated in humans. The spouses of identical twins tended to find the other twin annoying rather than attractive.
16. Mearns, Int. Paed. autistic individuals have a higher proportion of engineers as close family members than the rest of the population. Speculation on job choice and phenotype.
17.
18. Bandolier: incidence around 1993 http://www.jr2.ox.ac.uk/bandolier/booth/Vaccines/noMMR.html
19. Cited in New Scientist[6] and reviewed in Bandolier with graph of main results.
20. http://www.autism.org.uk/nas/jsp/polopoly.jsp?d=459&a=5576 Position statement, official website of National Autistic Society (UK) viewed March 2007
21. http://www.mrc.ac.uk/OurResearch/ResearchFocus/Autism/ResearchStrategy/index.htm
22. Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend analysis, Kaye JA, del Mar Melero-Montes M, Jick H, , , BMJ, 2001
23. [7]
24. [8]
25. http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15630056
26. [9]
27. Anne-Marie Plesner, Peter H. Andersen and Preben B. Mortensen
Kreesten M. Madsen, Marlene B. Lauritsen, Carsten B. Pedersen, Poul Thorsen. Thimerosal and the Occurrence of Autism: Negative Ecological Evidence From Danish Population-Based Data. Pediatrics 2003;112;604-606. PMID 12949291
28. Danish measurement artifact USA Today article by Dan Olmsted
37. Tebruegge M, Nandini V, Ritchie J. Does routine child health surveillance contribute to the early detection of children with pervasive developmental disorders? An epidemiological study in Kent, U.K. BMC Pediatr. 2004 Mar 3;4:4.
★ CPA-APC.org - Diagnosis and Epidemiology of Autism Spectrum Disorders Lee Tidmarsh, MD, Fred R Volkmar, MD, ''The Canadian Journal of Psychiatry'', Vol 48 pp 517–525, 2003
★ NIH.gov - 'The changing prevalence of autism in California', L.A. Croen, J.K. Grether, J Hoogstrate, S Selvin, ''Journal of Autism Developmental Disorders'' Vol 32, No 3, pp 207-15, June, 2002
★ NIH.gov -'The epidemiology of autistic spectrum disorders: is the prevalence rising?', Lorna Wing, D. Potter, ''Ment Retard Dev Disabil Res Rev'', Vol 8, No 3, pp 151-61, 2002
★ NIH.gov - 'The incidence of autism in Olmsted County, Minnesota, 1976-1997: results from a population-based study', W.J. Barbaresi, S.K Katusic, R.C. Colligan, A.L. Weaver, S.J. Jacobsen, ''Arch Pediatr Adolesc Med'', Vol 159, No 1, pp 37-44, January, 2005
★ California DDS figures and reports: http://www.dds.ca.gov/FactsStats/quarterly.cfm , http://www.dds.ca.gov/autism/autism_main.cfm
★ NeuroDiversity.com - Although labelled 'Prevalence of Autism' this lists references to incidence as well.
★ PediatricServices.com - 'The Autism Epidemic'
★ ScienceDaily.com - 'The Age of Autism: What epidemic?', Dan Olmsted, ''Science Daily'' (August 1, 2005)
★ ScienceDaily.com - 'The Age of Autism: The Amish anomaly', Dan Olmsted, ''Science Daily'' (April 18, 2005)
★ SFGate.com - 'State autism rate confounds experts: 273% increase in 11-year span', Katherine Seligman, ''San Francisco Chronicle'' (October 18, 2002)
★ TheAge.com.au - 'Number of disabled students soars' Chee Chee Leung ''The Age'' (April 26, 2005)
★ TMCNet.com - 'Parents say autism is an issue across the globe' (January 11, 2006)
★ Wired.com - 'The Geek Syndrome: Autism - and its milder cousin Asperger's syndrome - is surging among the children of Silicon Valley. Are math-and-tech genes to blame?' Steve Silberman ''Wired'' (December, 2001)
The reported 'incidence of autism' varies considerably among countries and is complicated by varying criteria for diagnosing autism, different standards for reporting public health problems, and other possible variations.
Background
Autism was first characterised in 1943 by psychiatrist Dr. Leo Kanner of the Johns Hopkins Hospital in Baltimore, and almost simultaneously, in German, by Dr Hans Asperger. Both published case series of children with strikingly similar features.
The number of children born in each year diagnosed with autism in countries reporting figures is larger now than then. The populations of those countries have also increased but it is unclear what change in the incidence fraction has occurred. Public health organizations and researchers are not yet confident they have completely determined causes for all changes in the rate of reports of Autism (''vide infra''). Potential factors listed by the UK National Autistic Society include:[1]
★ The underlying condition may have a changing incidence with time, i.e., more children (and/or more per thousand born) are affected by it;
★ More complete pickup of autism (case finding), as a result of increased awareness and funding;
;
★ Attempts in the US and UK to sue vaccine companies may have also increased case-reporting.
★ The diagnosis being applied more broadly than before, as a result of the changing definition of the disorder, particularly changes in DSM-III-R;[2] and DSM-IV [3]
★ Successively earlier diagnosis in each succeeding cohort of children including recognition in nursery (preschool) - this would affect apparent prevalence but not incidence
Incidence
The 'incidence' of a condition is the rate at which new cases occur in a population during a specified interval, e.g. "10 per year" or "12 in 1982". The 'prevalence' of a condition is the proportion of a population that are cases at a point in time, e.g. "1 in 1000". [4]
Examples of the way information is collected to specifically measure incidence rather than prevalence include:
★ Annual and age specific incidence for first recorded diagnoses of autism (that is, when the diagnosis of autism was first recorded);
★ Annual, birth cohort specific risk of autism diagnosed[5]
New diagnostic criteria and techniques
When the rising prevalence of autism spectrum disorders sparked research in the late 1990s, medical opinion initially attributed the increase to improved diagnostic screening or changes in the definition of autism. In 1994, the fourth major revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) was published[6] with updated criteria for the diagnosis of autism and autism spectrum disorders.[7] Professional medical associations, including the American Academy of Pediatrics, say that this revision was an important factor in increasing the apparent prevalence of autism and a 2005 study by Mayo Clinic researchers found increases in autism diagnoses followed the revisions in DSM criteria and changes in funding for special education programs.[8]
An increased awareness of autistic disorders by parents and pediatricians may have also led to increased reporting of Autism due to 'case substitution', which occurs when children with other disorders are identified as autistic.[9] This misdiagnosis may occur for several reasons including an increase in government funding for care of children diagnosed as autistic, but not for children with a similar degree of disability and need . If this is occurring, it means that children who in the past would probably have been diagnosed as having a different condition, or not diagnosed at all are recorded as new cases of autistic spectrum disorder. Possible alternate diagnoses include mental retardation, learning disability and childhood schizophrenia [10]. High-functioning autistic children are sometimes misdiagnosed ADHD.
[11] Children who are not primarily autistic, e.g. those with Fragile-X Syndrome (with characteristics that fit the criteria for autism) and even Down's Syndrome may have the diagnostic group with the best funding assigned.[12]
Incidence in sub-groups
There have been suggestions that the incidence of autism may vary amongst particular groups defined by occupation, lifestyle or genetic isolation. Changes that made travel and communication easier, and the growth of the technological industries during the past decade, have been suggested as means for increase in the proportion of couples likely to produce an autistic child. None of these have been established.[13] [14]
[15][16]
Geographical incidence
Japan
The Yokohama study in Japan (2005) examined the incidence of autism before and after the 1993 withdrawal of MMR, reporting 48 and 86 cases per 10,000 children in two sequential years before withdrawal, doubling to 97 and 161 per 10,000 afterwards in the two years afterwards.[17][18]
It studied over 30,000 children (278 cases) born in one district of Yokohama.[19]
United Kingdom
The National Autistic Society regarded the incidence and changes in incidence with time as unclear.[20] A 2001 review,[21] by the Medical Research Council, yielded an estimate of one in 166 in children under eight.
The reported autism incidence in the UK rose starting before the first introduction of the MMR vaccine in 1989.[5]
United States
After years of substantial annual increases, provisional data from the US Department of Education show a significant decrease in the number of new autism diagnoses recorded among children 3 to 5 years old. There were 1,451 new cases in 2001-2002; 1,981 in 2002-2003; 3,707 in 2003-2004; and 3,178 in 2004-2005, a drop of 529 new cases, or 14%.[23]
| Year | 2001-02 | 02-03 | 03-04 | 04-05 |
|---|---|---|---|---|
| New cases | 1 451 | 1 981 | 3 707 | 3 178 |
The incidence of autism increased by over 900% between 1992 and 2001, according to the United States Department of Education. In 1999, the autism incidence rate in the US was generally cited at 4.5 cases per 10,000 live births. By 2005, the US Centers for Disease Control (CDC) estimated one of every 250 babies was born with autism, or 4 cases per 1000.
Olmsted County, Minnesota
"The incidence of research-identified autism increased in Olmsted County from 1976 to 1997, with the increase occurring among young children after the introduction of broader, more precise diagnostic criteria, increased availability of services, and increased awareness of autism." The authors ascribed this to "improved awareness, changes in diagnostic criteria, and availability of services, leading to identification of previously unrecognized young children with autism." [25]
| Period | 1980-83 | 1995 to 1997 |
|---|---|---|
| Age-adjusted incidence of research-identified autism | 5.5 (95% confidence interval, 1.4-9.5) | 44.9 (95% confidence interval, 32.9-56.9) |
Denmark
In November 2002, a study reported a lower incidence of autism in Denmark than in the US and other countries. An incidence of 1 in 727 (738 out of 537,303) was reported, compared with up to 1 in 86 among primary school children in the United Kingdom and around 1 in 150 children in the USA. Danish authorities also reported a continued increase in the incidence of autism after 1992 after withdrawal of thiomersal-containing vaccines.[26] Data presented in 2003 shows a clear increase in incidence between 1990 and 1995 (before the criteria changed). Thus, the increased incidence of autism after the removal of thiomersal was not a measurement artefact,[27] nevertheless Dan Olmsted argued that this was an artefact due to a change in criteria for registration of children with autism in Denmark.[28]
Notes
1. 2618 Incidence National Autistic Society
2. [http://ajp.psychiatryonline.org/cgi/content/abstract/145/11/1404 DSM3 changes
3. DSM4 changes
4. British Medical Journal: Epidemiology for the Uninitiated 4th Ed: Quantifying diseases in populations BMJ
5. Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend analysis, Kaye JA, del Mar Melero-Montes M, Jick H, , , BMJ, 2001
6. [1]
7. [2]
8. The incidence of autism in Olmsted County, Minnesota, 1976-1997: results from a population-based study, Barbaresi WJ, Katusic SK, Colligan RC, Weaver AL, Jacobsen SJ, , , Archives of pediatrics & adolescent medicine, 2005
9. Am. Assoc. paed. Case substitution accounts for some of the increase in reported incidence
10. [3]
11. [4]
12. CNN report Dr Fred Volkmar, an autism researcher from Yale said "Autism is a kind of fashionable diagnosis".
13. Parental type
14. BBC report Simon Baron-Cohen believes that "it has become easier for systemizers to meet each other, with the advent of international conferences, greater job opportunities and more women working in these fields."
15. [5] Assortative mating has not been demonstrated in humans. The spouses of identical twins tended to find the other twin annoying rather than attractive.
16. Mearns, Int. Paed. autistic individuals have a higher proportion of engineers as close family members than the rest of the population. Speculation on job choice and phenotype.
17.
18. Bandolier: incidence around 1993 http://www.jr2.ox.ac.uk/bandolier/booth/Vaccines/noMMR.html
19. Cited in New Scientist[6] and reviewed in Bandolier with graph of main results.
20. http://www.autism.org.uk/nas/jsp/polopoly.jsp?d=459&a=5576 Position statement, official website of National Autistic Society (UK) viewed March 2007
21. http://www.mrc.ac.uk/OurResearch/ResearchFocus/Autism/ResearchStrategy/index.htm
22. Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend analysis, Kaye JA, del Mar Melero-Montes M, Jick H, , , BMJ, 2001
23. [7]
24. [8]
25. http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15630056
26. [9]
27. Anne-Marie Plesner, Peter H. Andersen and Preben B. Mortensen
Kreesten M. Madsen, Marlene B. Lauritsen, Carsten B. Pedersen, Poul Thorsen. Thimerosal and the Occurrence of Autism: Negative Ecological Evidence From Danish Population-Based Data. Pediatrics 2003;112;604-606. PMID 12949291
28. Danish measurement artifact USA Today article by Dan Olmsted
37. Tebruegge M, Nandini V, Ritchie J. Does routine child health surveillance contribute to the early detection of children with pervasive developmental disorders? An epidemiological study in Kent, U.K. BMC Pediatr. 2004 Mar 3;4:4.
References
★ CPA-APC.org - Diagnosis and Epidemiology of Autism Spectrum Disorders Lee Tidmarsh, MD, Fred R Volkmar, MD, ''The Canadian Journal of Psychiatry'', Vol 48 pp 517–525, 2003
★ NIH.gov - 'The changing prevalence of autism in California', L.A. Croen, J.K. Grether, J Hoogstrate, S Selvin, ''Journal of Autism Developmental Disorders'' Vol 32, No 3, pp 207-15, June, 2002
★ NIH.gov -'The epidemiology of autistic spectrum disorders: is the prevalence rising?', Lorna Wing, D. Potter, ''Ment Retard Dev Disabil Res Rev'', Vol 8, No 3, pp 151-61, 2002
★ NIH.gov - 'The incidence of autism in Olmsted County, Minnesota, 1976-1997: results from a population-based study', W.J. Barbaresi, S.K Katusic, R.C. Colligan, A.L. Weaver, S.J. Jacobsen, ''Arch Pediatr Adolesc Med'', Vol 159, No 1, pp 37-44, January, 2005
★ California DDS figures and reports: http://www.dds.ca.gov/FactsStats/quarterly.cfm , http://www.dds.ca.gov/autism/autism_main.cfm
External links
★ NeuroDiversity.com - Although labelled 'Prevalence of Autism' this lists references to incidence as well.
★ PediatricServices.com - 'The Autism Epidemic'
★ ScienceDaily.com - 'The Age of Autism: What epidemic?', Dan Olmsted, ''Science Daily'' (August 1, 2005)
★ ScienceDaily.com - 'The Age of Autism: The Amish anomaly', Dan Olmsted, ''Science Daily'' (April 18, 2005)
★ SFGate.com - 'State autism rate confounds experts: 273% increase in 11-year span', Katherine Seligman, ''San Francisco Chronicle'' (October 18, 2002)
★ TheAge.com.au - 'Number of disabled students soars' Chee Chee Leung ''The Age'' (April 26, 2005)
★ TMCNet.com - 'Parents say autism is an issue across the globe' (January 11, 2006)
★ Wired.com - 'The Geek Syndrome: Autism - and its milder cousin Asperger's syndrome - is surging among the children of Silicon Valley. Are math-and-tech genes to blame?' Steve Silberman ''Wired'' (December, 2001)
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