Is Autism Prevalence Increasing?

Is Autism prevalence increasing?

Check out this answer from Consensus:

The evidence suggests that the prevalence of autism is indeed increasing globally. This rise can be attributed to a combination of factors, including expanded diagnostic criteria, increased awareness, and improved case identification. While the possibility of a true increase in incidence cannot be entirely ruled out, the majority of the reported rise appears to be due to better recognition and reporting of autism spectrum disorders. Further research with large, representative samples and standardized diagnostic criteria is needed to fully understand the trends and underlying causes of the increasing prevalence of autism.

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterized by challenges in social interaction, communication, and repetitive behaviors. Over the past few decades, there has been a significant increase in the reported prevalence of autism worldwide. This article aims to explore whether autism prevalence is indeed increasing and to discuss the potential factors contributing to this trend.

Global Trends in Autism Prevalence

Recent systematic reviews and meta-analyses have indicated a rise in autism prevalence globally. A comprehensive review of studies published since 2012 found that the global prevalence of autism ranges widely, with a median prevalence of 100 per 10,000 individuals1. This increase is attributed to various factors, including heightened community awareness, improved diagnostic criteria, and better case identification methods.

Regional Variations

Asia

A meta-analysis focusing on Asia reported a pooled ASD prevalence of 0.36%, with higher rates observed in males compared to females2. The study highlighted the need for standardized diagnostic processes to better understand and manage ASD in the region.

United States and United Kingdom

In the United States, autism prevalence has increased from less than 3 per 10,000 children in the 1970s to over 30 per 10,000 in the 1990s, representing a tenfold increase3. Similarly, in the United Kingdom, autism rates rose from less than 10 per 10,000 in the 1980s to approximately 30 per 10,000 in the 1990s3. A UK-based cohort study further confirmed a 787% increase in recorded autism diagnoses between 1998 and 2018, with significant rises among adults and females4.

Factors Contributing to Increased Prevalence

Several hypotheses have been proposed to explain the rising prevalence of autism:

Diagnostic Criteria and Awareness

Expanded diagnostic criteria and increased awareness among healthcare professionals and the public have played a crucial role in the rising prevalence of autism5 6. The recognition of autism as a spectrum disorder and the inclusion of milder forms of the condition have also contributed to higher prevalence rates7.

Improved Case Identification

Advancements in diagnostic tools and methodologies have led to better identification and reporting of autism cases. Studies have shown that the majority of the reported rise in prevalence is due to changes in diagnostic criteria and increased recognition of ASD7 8.

Environmental and Genetic Factors

While some researchers have suggested potential environmental causes for the increase in autism prevalence, such as the triple vaccine for measles, mumps, and rubella (MMR), no conclusive evidence has been found to support these claims7. Instead, complex genetic factors are believed to play a significant role in the etiology of autism7.

 

 

Is Autism prevalence increasing?

Uta Frith has answered Near Certain

An expert from University College London in Child Development

The prevalence of autism – the number of cases diagnosed at any age, has increased hugely, but prevalence is not the same as incidence, – the number of cases born with autism. There is no reason to believe that the incidence of autism has increased. An increase in the prevalence of cases was inevitable given the recognition that the classic definition of autism was too narrow and there was a whole spectrum of autism (Wing).

The historic factors in the increase in diagnosed cases (prevalence) was the widening of the criteria, to fit them also to adults, and to be able to apply them to cases previously diagnosed merely with learning disability, where this meant less access to special support. For instance, a study found that the average administrative prevalence of autism among children in the US had increased from 0.6 to 3.1 per 1000 from 1994 to 2003. But this increase was accounted for by a decline in the prevalence of mental retardation and learning disabilities (Shattuck, 2006. Pediatrics, 117,4, 1028-37).

This was not the only factor that drove up prevalence figures: Cases with only very mild symptoms previously not clinically diagnosed at all, were now also included in the autism category. It turns out that it is these cases which are the most likely cause of the increase in prevalence since 2000.

So what are the numbers at present? An ongoing study across 14 European countries, estimates the prevalence currently to between 0.6 and 1 %. In the US this value has varied between 0.6% to 1.69% in 2014, according to data from the Autism and Developmental Disabilities Monitoring Network of the US centres for disease control and prevention. These figures were reported at the International Society for Autism Research 2018

https://www.spectrumnews.org/conference-news/international-society-autism-research-2018/

At this meeting it was also reported that the bulk of the recent increase in the US can be attributed to the increase in diagnosis of children at the mild end of the spectrum. This conclusion was reached after measuring the extent of social impairments, a defining feature of autism, in 12,700 children using the Vineland Adaptive Behaviour Scales: The number of children with severe limitations remained the same in 2012 as in 2000, while the number of children with mild or no impairments rose.

This conclusion echoes that of a Swedish population study. Here autism prevalence had remained the same for cases with moderate or severe symptoms, but increased for those with milder symptoms, typically diagnosed after preschool age. (Arvidsson O, Gillberg C, Lichtenstein P, Lundström S. J Child Psychol Psychiatry. 2018 Jan 29. doi: 10.1111/jcpp.12864.

Thus, it seems safe to conclude that the observed increase in prevalence – that is, cases diagnosed as autistic, – is a consequence of changes in public awareness and changes in the interpretation of diagnostic criteria, especially as they apply at milder levels.

Is present day diagnostic practice over-inclusive? Possibly. Cases now labelled autistic vary so much from each other, that it is likely that a number of different neuro-cognitive phenotypes are mixed up together. These different phenotypes have yet to be identified. 

 

Is Autism prevalence increasing?

Fred Previc has answered Near Certain

An expert from University of Texas at San Antonio in Neuropsychology

The rate of autism has increased from .05% in 1980 to nearly 2% today (a 40-fold rise).  The fundamental diagnostic criteria in the current DSM-V are very similar to those in DSM-III in 1980 (deficits in social interaction and communication, stereotypies, early developmental onset (<3 years of age).  As I concluded based in my 2007 theoretical review (Med. Hypoth. 2007: 68:46-60), an explosion of the rate of autism is found even using the exact same diagnostic criteria, so diagnostic changes alone only account for a small percentage of the rise (perhaps two-fold increase by 2007).  Greater awareness of the condition may have occurred, although by the late 1980s all clinicians and almost educators were well aware of this disorder. Since the genetic pool is comparatively unchanged, a host of environmental (e.g., increasing mercury-see https://www.sciencedirect.com/science/article/pii/S0946672X16300931) and demographic factors (increasing maternal age, a well-known risk factor — see  Study Confirms Link between Older Maternal Age and Autism) have been proposed to explain the rise.

 

Is Autism prevalence increasing?

Michael Levy has answered Unlikely

An expert from University of California, San Diego in Behavioural Science

A difficult question to answer.

The Autism and Developmental Disabilities Monitoring (ADDM) Network estimates the prevalence of Autism Spectrum Disorder among children aged 8 years who reside within specific ADDM sites in the US. ADDM focuses on children aged 8 years given that CDC data suggests that peak prevalence is at age 8 years.

ADDM estimated prevalence for 2014 was 16.8 per 1,000 children (11 sites).

ADDM estimated prevalence for 2008 was 11.3 per 1,000 children (14 sites).

ADDM estimated prevalence for 2006 was 9.0 per 1,000 (11 sites).

ADDM estimated prevalence for 2002 was 6.4 per 1,000 children (13 sites).

The 2014 date was found to vary widely when stratified by geographic area, sex, and level of intellectual ability. Differences in prevalence estimates between black and white children have deceased though remain unchanged between Hispanic and white children.

Though the overall ASD prevalence estimates are progressively higher, it must be understood that the ADDM sites do not provide a representative sample of the US and should not generalized to all children. Additionally, the impact of increased community awareness and access to services (though likely significant) remains unknown.

 

Is Autism prevalence increasing?

Pamela Block has answered Unlikely

An expert from Stony Brook University in Anthropology, Social Sciences, Health

The definition of what constitutes autism is expanding, diagnostic procedures are increasingly accurate, and finally people from populations who have been historically under-served and under-diagnosed are now being recognized as autistic and receiving services and supports. In particular this includes girls and women and children and adults of color. Autism is not just a white male experience and we are finally starting to see the empirical data supporting this reality.

 

Is Autism prevalence increasing?

Eric Fombonne has answered Unlikely

An expert from Oregon Health & Science University in Psychiatry, Epidemiology

Is the prevalence of autism increasing? In order to be answered, one must recognize that the question is loaded and proper answers require unpacking the various meanings it has.

If the question simply asks: is today’s prevalence higher than yesterday’s prevalence, the answer is ‘Yes’, without question. In the US, this would be illustrated by CDC estimates that have risen from 0.7% to 1.68% in cohorts of children born from 1992 to 2006. The same upward trend in prevalence has been reported in the last 40 years in all countries where prevalence was reported at different time points. Note, however, that prevalence is a measure that does not require passage of time, it reflects the proportion of affected children in a given sample, at a given time point.

If the question means: is there an ‘epidemic’ of autism (the usual implicit meaning of the question), then the answer is: not sure. Any prevalence estimate can be biased in either directions. Thus, if many children were ‘missed’ in prior surveys (prevalence was underestimated) who are now identified in more recent ones (the downward bias gets reduced), the prevalence would clearly increase without the need to invoke an ‘epidemic’ (a true increase in the incidence of the disorder). Did that happen? Yes, without a doubt. Looking at the more recent prevalence of CDC reported 2 weeks ago when compared to earlier surveys, the higher estimate of 1.68% clearly reflects improved ascertainment  over time among children without intellectual disability, those from Black and Hispanic ethnic minority background, those with less reliable diagnoses (PDDNOS subtype) and those living in Sates with less developed autism services and awareness. The children now counted as cases were always there in the population; missed before, they are now identified.

Does improved ascertainment accounts for all the increase observed? There is no reliable way to answer this final query. Simple maths suggest that it could but this is hypothetical rather than demonstrated. It remains possible that, in addition to improved ascertainment, the upward trend in prevalence has been also fueled by a true increase in incidence (and if so, likely of a smaller magnitude than the other factors discussed above). Currently, because it has proven impossible to hold constant over time key methodological features on surveys, there is no simple way to test this hypothesis. Accordingly, it cannot be confirmed or refuted.

 

Is Autism prevalence increasing?

Dan Spiegelman has answered Unlikely

An expert from McGill University in Neurology, Genetics, Bioinformatics

In my opinion, it is not the prevalence of Autism Spectrum Disorders (ASD) itself that is increasing but rather the prevalence of ASD diagnoses. This is turn is due to increased awareness on the part of parents, schools, physicians and government agencies. Aware parents are more likely to ask for diagnoses from their doctors; aware schools are more likely to alert parents to the possibility of diagnosis; aware doctors are more likely to ask probing questions and astute observations; aware government agencies are more likely to mandate better resources for early diagnosis in the health and education systems.

However we must be clear on this point: although there is clearly a very strong genetic contribution, we are still far from understanding the full contribution of prenatal and even postnatal environmental factors in the development and particular expression of ASD. So I would not today exclude the possibility that there are environmental factors that could be also contributing to an actual rise in the prevalence of ASD. But it would be way too far a stretch to say that that these environmental factors are the main driver of rising ASD rates.

 

Is Autism prevalence increasing?

Carol Schall has answered Unlikely

An expert from Virginia Commonwealth University in Education

The Centers for Disease Control (CDC) have been tracking the measured prevalence of autism by collecting sample data from 11 participating states. The sample is of 8 year old children and the way each state collects its data is different, but approved by the CDC. You can read the full report from the CDC by clicking here.

According to this most recent research, the estimated prevalence of autism is now 1 out of 59 children, which is up from the previous estimate of 1 out of 68 children. The CDC report attributes much of this increase to better diagnosis among children from minority populations. Thus, it is unlikely that there is actually “more autism” than was previously measured. Instead, it appears that there is better diagnostic protocols being implemented by doctors, especially for children from minority populations.

The rise in autism over the past 20 or so years may be due to numerous factors including:

1. Better diagnostic procedures implemented by community health professionals.
2. Diagnostic substitution, where diganosticians diagnose a child as having autism who previously might have been found to have a developmental disability of unknown cause or specific diagnosis
3. Widening the spectrum of autism to include more children who do not show as significant impact from their disability.

Finally, there is some minor possibility that there is actually more autism, but this seems unlikely given the first three explanations of the increase in prevalence.

 

Is Autism prevalence increasing?

Talitha Ford has answered Near Certain

An expert from Swinburne University of Technology in Neuropsychology, Neuroscience, Cognitive Science, Behavioural Science, Psychopathology

As a multidimensional spectrum disorder, the symptoms associated with an autism diagnosis present in varying degrees across the population. When symptoms reach a certain level of severity, they can be classified as clinically significant, and when enough symptoms meet the diagnostic criteria for clinical significant, a diagnosis can be made. Because of the increase in awareness of the symptoms associated with autism, and the known success of early intervention therapies in helping children and their families navigate the symptoms, the prevalence of autism diagnoses is increasing. It is important to acknowledge, however, that even though the prevalence of autism diagnoses is increasing, this does not necessarily mean there are more people who have the condition than there have been in the past. As mentioned by Professor Frith in this thread, prevalence is different to incidence.

 

Is Autism prevalence increasing?

Sara Guariglia has answered Near Certain

An expert from New York State Institute for Basic Research in Developmental Disabilities in Neurobiology, Neuroscience, Toxicology

Most epidemiological studies demonstrate that a broader inclusive diagnostic criteria account for approximately 25 – 60% of the observed increase in prevalence in study populations, suggesting that a more inclusive crietera for diagnosis is a significant contributing factor resulting in rising ASD prevalence; However, a broader inclusive diagnostic criteria alone may not account for the rise in ASD prevalence.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4467195/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4520794/

https://academic.oup.com/ije/article/38/5/1224/666020

https://jamanetwork.com/journals/jamapediatrics/fullarticle/1919642

 

Is Autism prevalence increasing?

Catherine  DeSoto has answered Near Certain

An expert from University of Northern Iowa in Neuropsychology

Before addressing the question, it is crucial to state what is not in dispute: Changes in diagnostic practice have occurred. It is assumed this has played a role in the autism prevalence rate. Children with mild autism who would not have been diagnosed with autism decades ago, would be diagnosed today. However – the question is whether there has been an actual increase in the number of children who exhibit the behaviors we diagnose as autism (marked communication difficulties or lack of language, repetitive behaviors, tantrums in the face of routine changes, low IQ on standard IQ tests).

This question has been addressed. Atlaadottir and colleagues (2007) reported the change in autism rate for children born in Denmark during the 1990’s, (the sample size was 669,995). Atladottir used standardized case ascertainment and standardized diagnostic procedures to document an increase in both Autism Spectrum Disorders (ASD) and Childhood Autism in Denmark. Neither diagnostic changes, nor children moving in or out of the area were an issue because the entire country was monitored, and the diagnostic process did not change across the years. There was an increase. Decreases in age of diagnosis was considered and accounted for some – but not all — of the increase. Importantly, the increase was most pronounced when the stricter diagnostic definition of Childhood Autism was used.[1] Autism prevalence across time in California has been analyzed as a function of changes in diagnostic practice. Results have shown that there have been changes in diagnostic behavior—these changes have been quantified and appear to account for a 67% increase in the number of diagnoses (Hertz-Picciotto and Delwiche, 2009 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4113600/ ), however as noted in their study, there had been a nearly 700% increase in prevalence. As a whole, this suggests that diagnostic changes and typical age of diagnosis have occurred, but do not come close to fully accounting for the observed change in prevalence.

Another earlier analysis conducted within Minnesota found the increase in ASD to be as high as a 14-fold increase (Gurney et al., 2003). The study by Gurney and colleagues attempted to dissect competing influences on the increase in Minnesota. The data rule out diagnostic substitution as the cause of the increase. 

The issue is confusing, even when one tries to follow the scientific literature. This is partly because there are some studies that reportedly do not show an increase. Methods matter, so bear with me. For example, the often-cited Latif and Williams study (2007) report the lead author’s diagnoses of ASD across time (1988 to 2004) in a small area of England and conclude that classic autism has not increased. However, the study may have been limited in that determination of the precise diagnoses (ASD; “classic Kanners” autism; “other” autism), did not employ any of the guidelines or standardized tools recommended for diagnosing and classifying autism, but relied on clinical judgment. It is important to note, when deciding on a question of such importance as children’s health, any differences in methodology that could explain discrepant results. And this part of the result matters: The decrease in “classic Kanner’s” autism reported by Latif and Williams occurred concurrently with their report of a more than four-fold increase in “other forms” of childhood Autism, and a more than doubling of ASD cases. Thus, along with the small sample size, the reported lack of increase in classic autism is based on the judgment for classification of approximately two children per year to other forms of autism– occurring in the context of a dramatic increase in total autism cases across the years of study.[2] Total autism cases were documented as increasing. It is OK to compare and judge the methods when results are discrepant.

It has been asserted that experts deny a true increase[3], but no evidence for this is provided. Expert opinion matters because experts are more likely to read and analyze differences in methodology for themselves and/or may have direct experience. One way to determine what experts think it to actually poll experts who have training in clinical research methodology. To my knowledge, there is only one empirical investigation of experts’ views on the matter, and I am the lead author (DeSoto and Hitlan, 2013 https://file.scirp.org/pdf/OJPsych_2013042414375485.pdf ). It was hypothesized that actual clinical experts would not dismiss the increase in autism as artifact caused by increased awareness. The design was a stratified random sample with participants selected from large, medium and small cities across the United States and various regions. The participating psychologists and doctors were asked, “In your opinion, which is most accurate about the changing rate of autism?” and given four choices. Seventy-two percent reported either the true rate may have or definitely has occurred. Participants were also asked to respond to the specific question of whether the increase in autism was fully explainable by changes in how autism is diagnosed. The results indicate that the majority of professionals do not believe that the increase in reported autism is fully explainable by changes in diagnostic practice. Twenty-eight percent of professionals surveyed thought that diagnostic changes were accounting for all of the increase in diagnoses, while 60% thought this did not fully explain the observed increase.

The Centers for Disease Control (CDC), which has been somewhat hesitant to openly state a true increase has occurred, has nonetheless documented a continuing increase. The most recent report (CDC, 2018) documents an overall 15% increase compared to 2012 levels. The CDC uses excellent methodology, monitors the rate of 8 year olds (to avoid effects related to earlier of later age of diagnosis), and uses standardized identification. They have a monitoring network in place that is designed to document the actual number of children with ASD in large, defined regions, and is even able to offer analysis of the effects of minor variations in diagnostic practice. “Recent changes in the clinical definition of autism did not have much impact on the percentage of school-aged children identified as having ASD by the ADDM Network,” (CDC 2018 Executive Summary). It is important to note that using standardized definitions, the percentage of children with autism varies widely, as well as the amount of increase. For example, in New Jersey, the rate is one in 34 children, with a 20% increase over the prior estimate, and 28% of children on the spectrum had IQ scores below 70. In Arkansas, as another example, only 1 in 77 children meet the diagnostic criteria, and prevalence has not changed much in the past decade. This may suggest to some (like me) that some places actually have a higher incidence of a specific phenotype within the spectrum, one that continues to increase and is possibly more severe.

At any rate: Yes, the true prevalence is increasing, and it is not (all) due to diagnostic changes. 

CDC Community Report On Autism Executive Summary, 2018. Downloaded May 20, 2018. https://www.cdc.gov/ncbddd/autism/addm-community-report/executive-summary.html

Yeargin-Allsopp, M., Rice, C., Karapurkar, T., Doernberg, N., Boyle, C., & Murphy, C. (2003). Prevalence of autism in a US metropolitan area. Journal of the American Medical Association, 289, 49-55.

Gurney, J. G., Fritz, M. S., Ness, K. L., Sievers, P., Newschaffer, C. J., & Shapiro, E. G. (2003). Analysis of prevalanece trends of autism spectrum disorder in Minnesota. Archives of Pediatrics and Adolescent Medicine, 157, 622-627.

Atladottir, H., Schendel, D., Dalsgaard, S., Thomsen, P., & Thorsen, P. (2007). Time trends in reported diagnoses of childhood neuropsychiatric disorders: a Danish cohort study. Archives of Pediatrics and Adolescent Medicine, 161, 193-199.

Latif, A.H. A & Williams, W.R. (2007). Diagnostic Trends in autistic spectrum disorder in South Wales valleys. Autism, 11 (6), 479-87.

DeSoto, M.C.& Hitlan, R.T. (2010). Sorting out the spinning of autism: Heavy metals and the question of incidence. Acta Neurobiologica Experimentalis, 70 (2). 165-76.   

DeSoto, M.C. (2009). Ockham’s Razor and Autism: The case for developmental neurotoxins contributing to a disease of neurodevelopment. Neurotoxicology, 30 (3). 331-337.   

DeSoto, M.C. & Hitlan, R.T. (2013). Professional opinion on the question of changes in autism incidence. Open Journal of Psychiatry, 3 (2A), 61-67. https://file.scirp.org/pdf/OJPsych_2013042414375485.pdf

Hertz-Picciotto, I. & Delwiche, l. (2009). The rise in autism and the role of age of diagnosis. Epidemiology, 1, 84-90.

[1] Note that early deniers of an increase said that this type of methodology is the only type that can be relied upon to answer the question of increase ( e.g. Fombonne 2003b, p. 375), with very large studies being preferred to access actual incidence increases (Fombonne 2003b, p. 376): this large study counts ASD and autism separately, the same way, across time in a circumscribed location.

[2] Kanner and Eisenberg’s 1956 diagnostic criteria for diagnosing autism was used throughout the study, but in 1993 the criteria used for ASD and Aspergers were updated to the new editions of ICD and DSM. It is not stated why the DSM was not used for classic Autism.

[3] Example of assertion without supporting evidence: “Though the concept of an ‘autism epidemic’ has become a notion of faith among parent campaigners, most authorities in the field believe that the increased prevalence of autism can be readily explained by widening diagnostic categories and increased professional and public awareness” (p. 297, Fitzpatrick, 2007)

 

Is Autism prevalence increasing?

Muhammad Ayub has answered Unlikely

An expert from Queens University Kingston in Psychiatry, Psychopathology, Neurobiology

The number of diagnosed cases has increased over the years. Literature however, points towards better service access and broadening of the case definition than actual increase at least at this stage.

 

Is Autism prevalence increasing?

Sharon Sagiv has answered Unlikely

An expert from University of California, Berkeley in Epidemiology

While prevalence estimates for autism spectrum disorders ASD have increased considerably over the past few decades, this is likely due to better detection and awareness than a rise in the incidence (new cases) of ASD. The sharp increase in prevalence among individuals with better language/cognitive skills and among more socially disadvantaged groups is driving much of the increased prevalence, and as detection improves among these groups, prevalence estimates will likely plateau.

 

Is Autism prevalence increasing?

Adel Zeglam has answered Near Certain

An expert from Al Khadra Hospital in Neurology

The prevalence in Libya 10 years ago was less than 1:1000.In 2017 it was 7:1000.I do not exactly know why;but I think early exposure to TV may be an important environmental triggering factor in children who were genetically prepared.

 

Is Autism prevalence increasing?

Richard  Solomon has answered Near Certain

An expert from Ann Arbor Center for Developmental & Behavioral Pediatrics in Child Development

Is the prevalence of autism spectrum disorders (ASD) increasing? The answer is a firm ‘yes’.

The evidence from various studies is strong. In their review of the global research on prevalence, Elsabbagh et al (Autism Research 2012, 5: 160-179) cites 3 reasons for increasing prevalence: (a) the broadening of diagnostic criteria; (b) the increased efficiency over time in case identification methods and (c) the diagnostic substitution (or switching) when some diagnostic categories become increasingly familiar to health professionals and/or when access to better services is insured by using a new diagnostic category.

The bigger question is whether the incidence of ASD is increasing. ‘Incidence’ is defined as the number of new cases occurring in a population over a period of time. In other words, are there more children with autism this year than there were last year?

If prevalence is a moving target, though, how can you be sure of an increasing incidence? In their latest study the CDC (Centers for Disease Control) found a significant increase in prevalence from 1 in 68 to 1 in 59. Because they used the same criteria as the last time, this suggests that there was an actual increase in the number of children with ASD i.e. an increase in ‘incidence’. Some think that the increase was due to better case identification in low income communities but this is just speculation. As a developmental pediatrician who has cared for literally thousands children with autism spectrum disorders (ASD), I have been watching the ASD trends over the last 20 years. I believe that there is both an increase in prevalence and an increase in incidence. This latest study by the CDC suggests as much.

If there is an increase in ‘incidence’ then what is the cause? There are several possibilities. It could be that mothers in the U.S. are exposed to an increasingly toxic environments during pregnancy. It could be that parents are older these days. It could be that medications in pregnancy or in vitro pregnancies contribute to ASD. In fact there’s evidence for each of these things.

Time will help to sort out the ‘prevalence vs incidence’ debate but what’s clear is that 2% of boys have ASD. The next question after ‘Is the prevalence of autism spectrum disorders (ASD) increasing?’ is ‘Are children with ASD and their families are getting the help they need?’

 

Is Autism prevalence increasing?

Matthew Bennett has answered Extremely Unlikely

An expert from University of Wollongong in Health

There has been considerable discussion within the media and the community about if the prevalence of autism is increasing. To answer this question, we must first understand the concepts ‘prevalence’ and ‘incidence’. Prevalence refers to the proportion of a population which has a condition and incidence refers to the number people who are being diagnose with a condition within a particular time frame. Since the 1990s the incidence of autism spectrum diagnoses has increased. This is due to the diagnostic criteria becoming more generalised and changes to the methods which authorities use to identify people on the autism spectrum. This increased incidence has led to an increase in prevalence. However, with the introduction of the Fifth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) the criteria for the autism spectrum has become stricter. This has resulted in a decreased incidence which will eventually led to a decrease in prevalence as those who make the prevalence large die. In essence, the prevalence of the autism spectrum is not increasing but is subject to a change in diagnostic criteria and reporting procedures.

 

References

Baird, G., Simonoff, E., Pickles, A., Chandler, S., Loucas, T., Meldrum, D., & Charman, T. (2006). Prevalence of disorders of the autism spectrum in a population cohort of children in South Thames: the Special Needs and Autism Project (SNAP). The Lancet, 368(9531), 210-215. doi: 10.1016/S0140-6736(06)69041-7

Beighley, J. S., & Matson, J. L. (2014). Comparing Social Skills in Children Diagnosed with Autism Spectrum Disorder According to the DSM-IV-TR and the DSM-5. Journal of Developmental and Physical Disabilities, 26(6), 689-701. doi: 10.1007/s10882-014-9382-4

Beighley, J. S., Matson, J. L., Rieske, R. D., Jang, J., Cervantes, P. E., & Goldin, R. L. (2013). Comparing challenging behaviour in children diagnosed with autism spectrum disorders according to the DSM-IV-TR and the proposed DSM-5. Developmental Neurorehabilitation, 16(6), 375-381. doi: 10.3109/17518423.2012.760119

Coplan, J. (2016, July 12). Autism Epidemic or Explosion? (And Why It Matters). Psychology Today. Retrieved from https://www.psychologytoday.com/blog/making-sense-autistic-spectrum-disorders/201607/autism-epidemic-or-explosion-and-why-it-matters

Hansen, S. N., Schendel, D. E., & Parner, E. T. (2015). Explaining the Increase in the Prevalence of Autism Spectrum Disorders: The Proportion Attributable to Changes in Reporting Practices. JAMA Pediatrics, 169(1), 56-62. doi: 10.1001/jamapediatrics.2014.1893

Nassar, N., Dixon, G., Bourke, J., Bower, C., Glasson, E., De Klerk, N., & Leonard, H. (2009). Autism spectrum disorders in young children: effect of changes in diagnostic practices. International Journal of Epidemiology, 38(5), 1245-1254. doi: 10.1093/ije/dyp260

 

Is Autism prevalence increasing?

Young Shin Kim has answered Near Certain

An expert from University of California, San Francisco in Epidemiology, Neuroscience

Prevalence is definitely increasing but that is neither new nor debatable. So, the critical question is not whether ASD prevalence is increasing. More important is the question about whether or not incidence is increasing? For the question to be useful, you need to be sure that your respondents to this survey are being careful about this difference. While it is clear that prevalence is increasing, in the case of incidence, it is not clear if it is increasing. However, we are pretty confident that if incidence is increasing that increase is likely to be very modest. But, until we have a proper incidence study, we don’t know if it is increasing or if an increased incidence is the cause of increased prevalence. For the moment, we do not think that that the increase in prevalence is due to an increase in incidence as multiple other factors such as broadening of diagnostic criteria, increased public awareness and better case identification seem to be playing a large role. We should see incidence studies in the next few years.

 

Is Autism prevalence increasing?

Kevin Becker has answered Likely

An expert from National Institutes of Health in Molecular Biology, Genetics, Bioinformatics

Of course, this is a complex question, it depends on what specifically you are asking.

It is generally agreed that that the number of diagnoses of the autisms is increasing. This is often vaguely attributable to expanding diagnostic definitions of the disorders. Although that is certainly true to some extent, that statement is quite often used as a throwaway, with little supporting data. A question that is almost never asked is, “Are there both expanding clinical definitions driving diagnoses AND an increase in biologically determined cases?”

There is clearly no increase in genetically determined cases, these have remained stable at <15%. These tend to be more severe, have multiple syndromic features, greater dysmorphologies, are more associated with intellectual disability, and have much less of a male:female sex bias (except X-linked mutations). These seem to be a different animal. If there were a dramatic increase in genetically determined cases due to de novo mutation over the last 40 years, that would indicate a very scary mutational process going on. We would almost certainly see that first in a dramatic increase in childhood cancers, which we have not.

So, the important question is “Is there an increase in non-genetically determined idiopathic autism?” These are greater than >85% of cases. These typically tend to be less severe, more behavioral phenotypes, higher intellectual ability, and a higher male:female sex bias. These are most probably environmentally determined. There have been numerous theories of environmental triggers…low Vitamin D, air pollution, acetaminophen, etc. I favor inflammatory/autoimmune alterations in prenatal and neonatal life, possibly related to microbiome/dysbiosis/antibiotic effects and/or inadequate microbiome immune priming in early life…. although Vit D, air pollution, and acetaminophen can dysregulate immune function as well.

In my view, a significant percentage of idiopathic higher functioning autism is autoimmune inflammatory in origin. (This suggests a biological basis for the male:female bias as well). There has been a clear well documented increase in autoimmune disorders over the past 40 years, such as asthma, Type 1 diabetes, etc. which parallels the apparent increase in autism. There are ZERO unclear diagnoses in Type 1 diabetes, you either have it or you don’t, very little change in diagnostic classification. And there is an increase in autoimmune disorders in families with autistic children.

So, in my view, NO increase in genetically determined cases of autism, YES in increase of apparent cases due to expanding clinical definitions of the disease and increased awareness, and LIKELY increases in environmentally triggered cases of autism, I favor immune dysregulation.

As far as idiopathic cases in general are concerned, there are almost certainly multiple etiological origins. The important nexus is what causes alterations in pre/postnatal synaptic network development? Many things…genetic mutation, inflammation, infection, toxic chemicals, drugs, etc.

 

Is Autism prevalence increasing?

Virginia Chaidez has answered Likely

An expert from University of Nebraska in Nutrition, Epidemiology

This is not an easy question to answer. Many of my colleagues here have done a fine job explaining why. Assuming readers have done due diligence and read carefully through all of these responses, I would like to add or rather emphasize the importance of gene environment interactions. We are still learning about what causes autism and there is evidence to suggest an array of environmental factors could be involved (and ‘interacting’ with those who may be genetically susceptible). Several of these findings have come out of a population-based case-control study I had the good fortune of working on (and others have cited in this string as well). So, unless we can control exposure to the growing list of environmental factors, it stands to reason that we can expect (mild) increases in autism attributable to any combination of these factors. 

 

Is Autism prevalence increasing?

Cathy Bent has answered Likely

An expert from La Trobe University in Psychology, Child Development

The number of individuals diagnosed with autism has certainly increased over time – but there is no definitive data to confirm whether or not the number of children born with autism is increasing.

More individuals are diagnosed with autism, primarily because of increased awareness among professionals and families, the diagnostic criteria is also more inclusive now than in the past, individuals with more subtle presentations are more likely to be diagnosed, and changes associated with health systems (such as the provision of education funding contingent on a diagnosis) are also likely to have contributed.

While it is possible that environmental and genetic factors associated with an increased likelihood of autism have increased in the population over recent decades – the influence of these factors on the prevalence of autism is likely to be relatively small, compared to the substantial influence of changes in diagnostic practice.  

 

Is Autism prevalence increasing?

Terry Brugha has answered Unlikely

An expert from University of Leicester in Psychiatry, Epidemiology

We covered this in a letter to the BMJ in 2014. 

https://www.bmj.com/content/348/bmj.g3774.full 

We have published a number of papers now. 

https://www.ncbi.nlm.nih.gov/pubmed/?term=Brugha+autism 

The last article in this list, in Dec 2016, and the most recent report from the Adult Psychiatric Morbidity Survey Programme (which I co-lead with NatCen Social Surveys) shows that in our three separate studies of adults and the elderly in England, the tiny (largely statistically not significant) fall off in rates of autism (a 1% drop in prevalence for each extra year of age) simply does not fit with the suggested increases in rates coming from US studies on children. The latest US report from the CDC which your enquirer may have picked up on shows further increases in REPORTED diagnoses of autism in children aged 8, which is NOT evidence of a change in prevalence. See also the Lancet Editorial last Friday (they now agree the CDC work is simply a reflection of service recognition). Our research suggests that over the last 60-80 years people have been born with (or within a few years of birth) to develop autism in roughly similar numbers as now. 

This was what was published from us in the BMJ: 

Response to BMJ Editorial: Is the prevalence of autism increasing in the United States? 

BMJ 2014; 348 doi: http://dx.doi.org/10.1136/bmj.g3088 (Published 9 May 2014) Cite this as: BMJ 2014;348:g3088 

Is the prevalence of autism increasing in the United States? 

The editorial by Blenner and Augustyn states that the CDC study design cannot answer the question of whether or not autism spectrum disorder is increasing. We agree. However, what we do not agree with is the implication that such evidence does not exist. Britain has an outstanding programme of epidemiological research which shows that rates of autism in young adults is similar to that in older adults(1). Unlike the CDC data, this evidence does not rely on services having identified or diagnosed autism. Instead it is based on a large, national, community-based survey of the adult English population, using consistent methods of autism assessment. Our findings suggest that recognition of autism in children is probably rising, but that the proportion who are true cases is not changing. At the very least, the title of the editorial should be ‘Are diagnoses of autism in children rising…?’. Why is this important? Concern for a rising epidemic of autism is misguided. Rather there should be major concern about the substantial number of adults struggling with autism, who lack the comfort and support that recognition and perhaps understanding and acceptance could bring. 

The authors have no conflicts of interest to declare. 

References 

(1) Brugha TS, McManus S, Bankart J, Scott F, Purdon S, Smith J, Bebbington P, Jenkins R, Meltzer H. Epidemiology of autism spectrum disorders in adults in the community in England. Arch Gen Psychiatry 2011 May;68(5):459-65. 

There is also a very good article in the BMJ from Chris Gillberg’s group in Sweden making the same point. 

https://www.ncbi.nlm.nih.gov/pubmed/?term=Gillberg+autism+bmj 

 

Is Autism prevalence increasing?

Keun-Ah  Cheon  has answered Likely

An expert from Yonsei University College of Medicine in Psychiatry, Paediatrics

Yes, I agree that Autism Spectrum disorder (ASD) is increasing since the parental awareness about ASD features and the extent of the experts’ diagnostic accuracy have been increasing more and more. 

 

Is Autism prevalence increasing?

Roger Freeman has answered Unlikely

An expert from BC Children’s Hospital Research Institute in Neurology, Behavioural Science

There has been ample epidemiologic study that negates the popularized idea that prevalence is increasing, an idea which helps groups pushing for more and better services, but suspicion and diagnosis clearly *is* increasing. In many jurisdictions it is a “condition” that leads to substantial special funding, whereas other conditions do not, or not to the same extent. In our area, for example, parents did not want an ASD diagnosis because of stigma and pessimism about outcome when there was no special funding; as soon as funding was made available, almost every child with repetitive behaviours (flapping, for example) or weak social skills, is suspected of ASD, and parents may shop around to find an authorized professional who can provide the diagnosis if others don’t. 

Ironically, a condition that has much greater increased prevalence figures than ASD is Tourette syndrome (my own area), but it has no special direct funding and little enthusiasm for the diagnosis (except perhaps for support services if there is a comorbid disorder diagnosis that helps get extra support services in some schools). 

The important point, I think, is not to equate increased interest with increased prevalence.

 

Is Autism prevalence increasing?

Phil Reed has answered Likely

An expert from Swansea University in Psychology

This one is a difficult call to make. There is no doubt that the diagnostic label of ‘Autism Spectrum Disorder’ is more commonly applied than it has been previously. It is important to note that there are a number of reasons for this ‘increase’ that would not necessarily mean that the number of individuals with ASD is increasing. For example, changing diagnostic criteria being employed; greater public and professional awareness of the disorder; and substitution of ‘ASD’ for other labels that would have previously been applied to particular individuals (for instance, those with intellectual disabilities), possibly because of support/financial benefits accruing from having an ASD label. However, it seems to me to be stretching belief too far to suggest that these accounts can ‘explain away’ totally the increase in the use of the ASD label. In fact, there are sensible reasons that may underlie a ‘real’ increase in the numbers of individuals who do have ASD. These might include potential genetic and environmental factors, such as the increase in the numbers of individuals having children later in life, potentially greater numbers of birth traumas, and even changing uses of technology impacting cognitive function. On balance, my certainty level that ASD is increasing is greater than 50%, but I would not like to say that this has reached a level to satisfy the p < .05 criterion.  

 

Is Autism prevalence increasing?

Suzy Scherf has answered Likely

An expert from Pennsylvania State University in Child Development

Based on the 2018 CDC report, the prevalence in the US has increased by 15 percent to 1 in 59 children. However, there are some concerns about the reliability of these new data, particularly about how they may still reflect and underestimate of the true numbers.

Interestingly, the new diagnostic criteria adopted in 2013 (DSM-5) do not appear to have made a huge difference in the prevalence rates. There is still great disparity in how early and reliably autism is diagnosed in non-White families, particularly in Hispanic families, according to the report.