An extremely low prevalence of autism in Quito, Ecuador

The title of this post is taken from the paper by Laura Dekkers and colleagues [1] (open-access) who sought to "get an estimate of ASD [autism spectrum disorder] diagnoses in children and adolescents aged between of five and fifteen at regular schools in Quito."

So, the starting point: "Ecuador has more than 14 million inhabitants... of which over 1.6 million are estimated to live in the capital city of Quito." As part of the "law requiring inclusive education", the authors decided to survey for "cases of ASD in regular schools" in Quito. Said schools were identified via the databanks of the Ministry of Education, of which 161 schools were eventually selected for analysis including just over 51,000 pupils aged 5-15 years. Cases of ASD within that population were "identified by the school administration" and included both autism spectrum diagnoses via DSM-III and DSM-IV criteria.

Results: 33 schools (~20%) reported having at least one pupil officially diagnosed on the autism spectrum. Interestingly the authors report that there was a possible relationship between school reporting one or more pupils on the autism spectrum and the size of the school - "the probability of reporting at least one pupil with an ASD diagnosis decreasing with the size of the school."

"Of the total number of pupils within all schools (N = 51,453) only 57 pupils had an official diagnosis of ASD. This brings the prevalence of ASD in Quito, as reported by schools for regular education, to 11.07 out of 10,000, which is 0.11 %." Most of those diagnosed were so with the label 'PDD-NOS' (Pervasive Developmental Disorder - Not Otherwise Specified). Bearing in mind the small numbers detected, the male: female ratio came in with a familiar statistic - "4.7 times more boys than girls" and mean age at diagnosis was a very poor 7-8 years of age.

Then another statistic: "Out of the 161 schools, 59 schools (36.6 %) mentioned that they thought that at their school there was at least one pupil who did not have an ASD diagnosis, but should have been diagnosed with ASD." In total there were 108 pupils falling into this 'maybe' category. And finally: "Out of all schools (N = 161), 14 schools (8.7 %) reported that they had at least once refused a boy or girl with ASD to their school, because of his or her behavior."

There are a few points to make about the Dekkers findings, some of which the authors already make themselves. First is the quite low prevalence rate estimated from their research. To quote (again): "We propose that the found percentage of 0.11 % reflects the current probability of receiving a diagnosis of ASD in Quito, Ecuador, rather than the proportion of the population that has ASD." Indeed, the authors provide a list of various factors that might have been contributory to the low prevalence rate estimated for autism in Ecuador including issues with accessibility to diagnostic services, the general lack of awareness of autism in the country and the stigma that still surrounds the label ("Autism is often not recognized as such and considered a punishment of God, leaving the family in shame hiding their child with problem behavior"). One might also entertain the notion that autism may not be as prevalent in Ecuador as other countries for genetic / biological or environmental reasons too; perhaps even learning some lessons from other labels (see here).

Second, we can expect more data from this group on this topic. "The ASD prevalence in special education was the second part of phase 1 of the PAE [Prevalence of Autism in Ecuador] project, including 11 special schools and centers, and a total of 1195 pupils; publication of the results is in preparation. We can expect a higher prevalence at these schools, because there is a trend for higher and increasing prevalence of autism in special education in areas with low prevalence of autism." I believe we have a few clues there as to what they found.

Finally, what is missing from the Dekkers data is information about the children themselves outside of just diagnosis and age. Things like whether comorbidity such as ADHD [attention-deficit hyperactivity disorder] is part of the clinical picture in light of what is known about a possible relationship (see here). Indeed, whether part of the low autism prevalence estimate suggested might also part of a wider trend in child psychiatry in Ecuador, and whether we can expect to see increasing rates as per other data from other countries [2]?

Music to close: Sash! - Ecuador.

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[1] Dekkers LMS. et al. Prevalence of Autism Spectrum Disorders in Ecuador: A Pilot Study in Quito. Journal of Autism and Developmental Disorders. 2015. Aug 30.

[2] van Bakel MME. et al. Low but Increasing Prevalence of Autism Spectrum Disorders in a French Area from Register-Based Data. JADD. 2015; 45: 3255-3261.

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Dekkers, L., Groot, N., Díaz Mosquera, E., Andrade Zúñiga, I., & Delfos, M. (2015). Prevalence of Autism Spectrum Disorders in Ecuador: A Pilot Study in Quito Journal of Autism and Developmental Disorders DOI: 10.1007/s10803-015-2559-6

Autism prevalence across the DSMs

IMFAR (International Meeting For Autism Research) is probably the biggest meeting of minds conferences for autism. I have, unfortunately, never attended the conference, not even when it came to the shores of Blighty back in May 2008. I do however take a great interest in the various talks and presentations given at the conference appearing in the searchable conference abstracts book on-line. Whilst reading through this years list (2011), I happened upon this interesting study* on the prevalence of autism. It is interesting because it is the kind of study that I have often thought needed to be done on prevalence, given the multitude of possible reasons why the prevalence of autism might be increasing.

The study (for which I only have the abstract) applied 3 versions of the the Diagnostic & Statistical Manual (DSM) - DSM-III (1980), DSM-IIIR (1987) and DSM-IV TR (2000) - on behavioural and developmental information taken from records of just over 5,000 8-year old children suspected to have an autism spectrum disorder (ASD) from a total population of 280,423. The authors reported the numbers of cases fulfilling criteria for autism and the wider pervasive developmental disorder (PDD) according to the version of DSM used:

• DSM-III (1980) autism = 1921, PDD = 2232
• DSM-IIIR (1987) autism = 1892, PDD = 2223
• DSM-IV TR (2000) autism = 2054, PDD = 2641

They then calculated the autism and PDD prevalences (per 1000) based on the total population figure (280,423):

• DSM-III (1980) autism = 6.9, PDD = 8.0
• DSM-IIIR (1987) autism = 6.7, PDD = 7.9
• DSM-IV TR (2000) autism = 7.3, PDD = 9.4

As you may see from the figures, the prevalence of core autism seems to remain fairly constant across the various DSM versions although perhaps shows a slight upward spike using the 2000 version. The prevalence for the wider PDD category is a little more variable; indeed more so when the DSM-IV TR criteria is used. Bear in mind that this is data based on the same group of 8-year old children. I think that this quite good support for saying that at least some of the increase in prevalence is due to the changes in diagnostic criteria. Based on these figures it suggests that about 18% of the increase in the wider PDD diagnosis might be due to changing criteria (I think!).

One might ask why DSM-IV (1994) was also not included in the dataset, but I think the changes made in DSM-IV TR from DSM-IV were more cosmetic than structural (both DSM-IV TR and DSM-IV define Asperger syndrome where DSM-III did not specifically do so). Combined with the issue of diagnostic substitution covered in a previous post, you can perhaps see that at least some of the increase in prevalence is due to factors other than a 'real' increase in cases. 

That is however not to say that all of the increase is due to such diagnostic factors. In the words of Prof. Sir Michael Rutter back in 2005 "a true risk due to some, as yet to be identified, environmental risk factor cannot be ruled out" (I will be coming back to Prof. Rutter in future posts). That added to an increasing prevalence and incidence of autism in certain geographical areas, leaves the door slightly ajar for maybe not just one environmental factor but quite a few, either working alone or cumulatively, spread evenly or not evenly geographically, impacting on the numbers of cases being diagnosed.

A final note. This paper appeared recently comparing DSM-IV TR and the proposed DSM-V criteria for autism. At the moment I don't have the full-text paper so cannot extensively describe and discuss. From the abstract it appears that some kind of comparison was made between those diagnosed with DSM-IV and might happen if DSM-V draft criteria were applied to the same group(?). The authors conclude in the abstract that DSM-V might be less sensitive regarding identification for those presenting with Asperger syndrome and high-functioning autism. What this might do to prevalence figures post-2013 publication is 'interesting'. I wait to see more. 

Thanks IMFAR and keep up the good work.

*Reference: Rice CE, Wiggins LD, Carpenter LA, Schieve LA, Fitzgerald RT, Pedersen A, Lee LC. Variation in the prevalence of the Pervasive Developmental Disorders by diagnostic criteria. IMFAR 2011.