In recent years, studies have revealed an increase in prevalence rates of Autism and other Pervasive Developmental Disorders (PDD). The causes for such increases are not entirely understood, but may reflect factors such as study methodology, improved methods of detection and widening of diagnostic criteria.
To determine prevalence rates of Autism and other PDD among Anglophone, school-aged children in
23,664 children aged 4 to 17 years old were surveyed from the English Montreal School Board (EMSB). All the data was obtained from educational records and therefore, no direct examination of any children was required for this research. Children with a diagnosis of a PDD at the EMSB are assigned a special education code of 50. The special education codes are finalized by the end of March each year, and therefore, we selected a survey date of April 1, 2008. For all children with a diagnosis of PDD, information was obtained about their diagnostic subtype, age of diagnosis, current age, gender, current grade, the location of their diagnosis and the school they were attending. Prevalence rates were then calculated.
Out of a population of 23,664 children enrolled in the 71 schools of the EMSB, a total of 206 were identified by a special education code of 50 with a diagnosis of a PDD. The prevalence for all PDD was 8.71/1,000 (95% CI: 7.56 - 9.96 /1,000). For PDD specific diagnoses, the prevalence was 2.87/1,000 (95% CI: 2.23 - 3.64/1,000) for Autistic Disorder, 4.61/1,000 (95% CI: 3.78-5.55/1,000) for PDD-NOS, 1.18/1,000 (95% CI: 0.79 - 1.71/1,000) for Asperger Disorder, and 0.04/1,000 (95% CI: 0.00 - 0.24/1,000) for Childhood Disintegrative Disorder. There was a significant linear increase in birth cohort prevalence proportions from older (Grade 11) to younger (Kindergarten) birth cohorts. In the sample, there were 174 males and 32 females resulting in a 5 to 1 male to female ratio. Of the 206 children with PDD, 16 attended a special needs school and 190 attended a regular school. Of the 190 attending a regular school, 16 were placed in segregated classrooms, while 174 were placed in integrated classrooms. Of the 174 attending integrated classrooms, 165 were assigned a child-care worker and 9 did not have any child-care worker to facilitate their integration.
This study provided additional evidence that the prevalence rate of ASD is close to 1%, as per several recently published surveys. Recent birth cohorts yielded significantly higher rates than older ones. The reasons for this trend could not be examined with our methods.