One
in 165 children now estimated to have pervasive developmental disorder,
three times greater than previously thought
Eric Fombonne, MD, FRCPsych
Prevalence
of PDD in Canadian childen aged 0-19 |
||
| This table shows the estimated number of Canadian children with PDD, by province, based on 2001 Census data and a prevalence rate of 60/10,000. Current numbers would be higher, about 48,000 Canadian children. | ||
| PROVINCE |
POPULATION
|
CHILDREN WITH PPD |
| Newfoundland and Labrador | 128,220 |
769 |
| Prince Edward Island | 36,875 |
221 |
| Nova Scotia | 226,775 |
1,361 |
| New Brunswick | 180,770 |
1,085 |
| Quebec | 1,753,650 |
10,522 |
| Ontario | 3,002,165 |
18,013 |
| Manitoba | 314,140 |
1,885 |
| Saskatchewan | 285,540 |
1,713 |
| Alberta | 840,550 |
5,043 |
| British Columbia | 976,350 |
5,858 |
| Yukon | 8,325 |
50 |
| Northwest Territories | 13,060 |
78 |
| Nunavut | 12,445 |
75 |
| Total for Canada | 7,778,865 |
46,673 |
Recent studies in Canada and the United Kingdom show pervasive developmental disorder (PDD) to be much more common than previously thought with about 60 children in every 10,000, or one in 165, afflicted.
PDD is a term often used interchangeably with autism spectrum disorder to describe several closely related disorders. These disorders, which include autistic disorder, Asperger syndrome, atypical autism and disintegrative disorder, share the same essential features (i.e. impairments in communication and social interaction combined with restricted interests and patterns of behavior) but differ on specific symptoms, age of onset, or natural history.
A few years ago, my colleagues and I conducted a thorough survey of PDD in preschoolers in the Midlands (UK).1 The study was set to identify PDDs (not only autism), used very proactive techniques to identify cases in the community and relied on modern diagnostic tools to confirm caseness. We reported a rate of 62/10,000. Only two other studies had reported comparable rates at that time, and caution was therefore needed to interpret these figures.
Three years later, the results of six new studies have become available. Two of these studies report rates around 30/10,000 but these estimates likely represent underestimates due to the particular design features of these investigations (i.e. no direct examination of children, less sensitive case finding methods). The other four yield, once again, rates around the 60/10,000 figure.
In the same area of the Midlands, we surveyed with rigorously identical methods children from more recent birth cohorts and replicated our previous findings.2 We are also conducting the first ever survey of PDDs in Quebec, and our preliminary results indicate a high prevalence estimate (67/10,000) among 28,000 school age children in Montreal.3
In light of this new data coming from independent surveys, it can now be said with much more confidence that the rate of PDD is about 60/10,000. This represents one child out of every 165.
In Canada, there are about 8 million young people in the age group 0-19. Applying a rate of 60/10,000 (or 0.6%), we can estimate that there are currently 48,000 young people from that age group suffering from a PDD today in Canada. This count does not reflect the adult population.Does this mean there is an epidemic of PDD? Not at all. We believe the high rates we are seeing are the result of a combination of factors. With improved recognition of the symptoms, diagnosis of PDD is now being made more frequently and at an earlier age, thus increasing the number of children being diagnosed. More rigorous methods used in recent surveys have also improved our ability to find cases of PDD. The lower rates found in two of the most recent studies, for instance, most certainly reflect less sensitive case finding approaches.
While it is true that there are a couple of studies with high rates but not particularly sensitive methods, there is otherwise no direct evidence to support an increased incidence, or epidemic, of PDD. Our repeat survey in the Midlands showed the same rate as the earlier survey, indicating that there is no true rise in the incidence.
The bottom line is that PDD is more common now because our tools for finding and diagnosing children are better.
1 Chakrabarti S, Fombonne E. Pervasive developmental disorders in preschool children. Journal of the American Medical Association (JAMA) 2001;285(24):3093-3099.
2 Chakrabarti S, Fombonne E. Pervasive developmental disorders in preschool children: high prevalence confirmed 2004 (submitted)
3 R. Zakarian, A. Bennett, D. McLean-Heywood, E. Fombonne. Prevalence of PDD amongst english speaking school-aged children in Quebec. Presented at the 7th Congress Autism Europe Lisbon, Portugal, November 14-16, 2003.
Eric Fombonne holds a Canada Research Chair in Child Psychiatry at McGill University and heads the McGill University Division of Child Psychiatry at the Montreal Children’s Hospital. He is a Fellow of the UK Royal College of Psychiatry (FRCPsych) and serves on the scientific committees of several international organizations and research institutes