Age at diagnosis of autism spectrum disorders in four regions of Canada.
In many cases, autism can be diagnosed reliably between two and three years of age,(6-9) although often children are not identified until they are older. (10-14) Several studies have reported decreases in the age at which children are diagnosed with autism when comparing birth cohorts (15,16) or year of diagnosis, (17) while other studies have found an increase in age at diagnosis across birth cohorts (although not statistically significant), (12) or no clear trend over time. (18) Geographic differences have also been reported. For example, the median age at first autism diagnosis ranged from 49 months in Utah to 66 months in Alabama, based on surveillance data for children who were 8 years old in 2002. (4)
There is little information on the age at which Canadian children are first diagnosed with autism, apart from one study that used administrative data to estimate the prevalence of autism among children in Manitoba and Prince Edward Island (PEI) in 2002. In those provinces, the median age at diagnosis was 3.7 and 3.6 years, respectively. (19) The objectives of the current analysis were to determine: 1) the age at which children in various regions of Canada are first diagnosed with autism; 2) whether geographic variations in age at diagnosis exist; and 3) whether there is a trend towards earlier diagnosis in more recent years. We also examined whether there are differences in age at diagnosis between boys and girls and across diagnostic subtypes.
Data source and sample
The National Epidemiologic Database for the Study of Autism in Canada (NEDSAC) was established in 2001. It functions as a surveillance program for diagnosed cases of autism among children in various regions of Canada. Because the delivery of health, social services and education differs across provinces, different protocols were adopted in the surveillance regions with the goal of achieving maximum case ascertainment in the most cost-effective manner possible (see Table 1). Ethics approval was obtained from the PEI Research Ethics Board, and from research ethics boards at the University of Manitoba, Queen's University, and Memorial University for ongoing surveillance in PEI, Manitoba, Southeastern Ontario, and Newfoundland and Labrador, respectively. NEDSAC contains the date of birth and sex of all children identified by participating agencies in the surveillance regions. Depending on the amount of information that is available in files (Manitoba), or whether the family consents to provide more detailed information to the research team (Southeastern Ontario, PEI, Newfoundland and Labrador), the database also contains information on whether the child is adopted, number of siblings and number of siblings with autism, first three digits of the postal code of the child's current residence, birthplace, maternal and paternal age, ethno-cultural identity, diagnostic subtype, date of diagnosis, who made the diagnosis, and the tests that were used.
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For the current analysis, we included children identified for NEDSAC from the time data collection began (2002 in Manitoba and PEI; 2003 in Southeastern Ontario and Newfoundland and Labrador) up until May 2007, who: 1) were first diagnosed with autistic disorder, PDD-NOS, Asperger's disorder, or a non-specific diagnosis of autism spectrum disorder between 1997 and 2005, inclusive, and whose month of diagnosis was known; and 2) were born in one of the surveillance regions and still living there in the year when diagnosed, or, if they were born elsewhere, diagnosed either in the same year they moved to the surveillance region or in a subsequent year.
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Age at diagnosis is reported using medians and interquartile ranges due to the variable's skewed distribution (see Figures 1-5). We used SPSS 16.0.1 (SPSS Inc., Chicago, IL) and the Mann-Whitney or Kruskal-Wallis test to compare inter- and intra-regional findings for age at diagnosis by sex and diagnostic subtype (i.e., autistic disorder, PDD-NOS, Asperger's disorder, or general diagnosis on the autism spectrum ("ASD")), and inter-regional differences by three-year period in which the initial diagnosis was made (1997-1999, 2000-2002, 2003-2005). The Spearman's rank correlation was used to examine intra-regional trends by three-year period of initial diagnosis. For Manitoba--the only region with a sufficient sample size to conduct a stratified analysis--we also examined, for each diagnostic subtype, whether the age at diagnosis increased or decreased significantly by three-year period of initial diagnosis, using Spearman's rank correlation. All references to significance are based on two-tailed tests using an alpha of 0.05. We did not consider any adjustment of this alpha level for multiple testing because of the exploratory nature of the study.
Figures 1-5 illustrate the distribution of age at diagnosis for the combined sample and for each region. Table 2 reveals significant inter-regional differences in the median age at diagnosis overall (p<0.001) and for boys (p<0.001). Girls were diagnosed later than boys in all regions, although none of the differences was significant. The age at diagnosis differed significantly across regions for two time periods: 2000-2002, and 2003-2005. In Southeastern Ontario, it increased significantly over time (p = 0.004).
Significant inter-regional differences were observed for the median age at diagnosis of PDD-NOS and ASD. The age at which children were diagnosed with PDD-NOS was highest in Manitoba (77.0 months) and lowest in Newfoundland and Labrador (48.0 months). For the ASD category, Southeastern Ontario had the highest median age of diagnosis at 47.0 months, compared to 36.0 months for Newfoundland and Labrador. Significant differences in age at diagnosis for the diagnostic subtypes were found within all regions. Children with autistic disorder or ASD were diagnosed the earliest, followed by those with PDD-NOS. Children with Asperger's disorder were more likely to be diagnosed when they were older. For almost all the subgroup analyses, Newfoundland and Labrador had the lowest age at diagnosis. The only exception was for autistic disorder, which was diagnosed earliest in Southeastern Ontario (34.0 months).
Table 3 shows that there was a significant increase over time in the median age at diagnosis of PDD-NOS in Manitoba (p = 0.021). An increase over time was also observed for Asperger's disorder in that province, but it was not significant.
The Senate Standing Committee on Social Affairs, Science and Technology, in its final report on the enquiry into funding autism treatment in Canada, noted there are waiting times for assessment and diagnosis, and parents frequently are "unable to access timely assessment and diagnosis of their children". (20) Although many cases of autism can be diagnosed reliably between two and three years of age, (6-9) in three of the surveillance regions (Manitoba, Southeastern Ontario, PEI) about half the children were not diagnosed until four years of age or more.
Overall, Newfoundland and Labrador had the lowest median age at diagnosis. In that province, there is a "zero" waitlist policy for early intervention for preschool children diagnosed with autism. There may be more incentive for earlier diagnosis in regions with reduced waiting times for services. In contrast, Southeastern Ontario had the highest median age at diagnosis. One possible explanation for this is the large proportion of children identified with Asperger's disorder in that region (24.8%) compared to elsewhere (less than 12%). In all regions, consistent with findings from other studies, (10,14,15,21) children with Asperger's disorder were diagnosed later than children with PDD-NOS or autistic disorder.
Southeastern Ontario had the highest median age at diagnosis overall, yet children with autistic disorder were diagnosed earlier there than in any other region. Any child with autism who meets the age criteria is eligible for provincially funded intensive behavioural intervention programs in Manitoba, PEI, and Newfoundland and Labrador. In contrast, only children with autistic disorder or those on the severe end of the autism spectrum are eligible for the program in Ontario. (22) One hypothesis for the anomalous finding for age at diagnosis of autistic disorder in Southeastern Ontario then is that assessment resources tend to be focused on the more severe cases, who may be eligible for provincially funded early intervention services.
Southeastern Ontario was also the one region where the age at diagnosis increased over time. In Manitoba, where the sample size was sufficient to conduct an analysis of age at diagnosis stratified by diagnostic subtype and year of initial diagnosis, temporal increases in age at diagnosis were observed for Asperger's disorder and for PDD-NOS. One possible explanation for these findings is that older, higher-functioning children who were not diagnosed in the past may be more likely to receive an autism diagnosis as awareness of the autism spectrum increases.
Several cautions and limitations of the methods need to be taken into account when interpreting the findings. Some investigators have compared birth cohorts when examining whether the age at which children are diagnosed with autism is decreasing. (12,15,16) We chose to use calendar years instead, as children who were born in more recent years (e.g., late 1990s and early 2000s) may not yet have been diagnosed with autism, which would bias the results towards a younger age at diagnosis in later birth cohorts. Accordingly, it is not possible to directly compare our findings with those from studies that have examined age at diagnosis for birth cohorts. It is also important to note that the analysis presented in this paper did not include all children who were diagnosed with autism between 1997 and 2005 in the surveillance regions. NEDSAC does not contain information on children who moved from the surveillance regions before data collection began in 2002/2003. It is unlikely, however, that migration is related to age at diagnosis, and therefore the non-inclusion of these children would probably not affect the findings greatly. We also excluded from the analysis cases for whom the month or year of diagnosis were unknown, as well as cases whose residence in the surveillance regions during or prior to the year in which they were diagnosed could not be confirmed. To assess what effect the exclusion of these two groups of children might have on the findings, we examined the age and sex of children who were included and excluded from the analysis. No significant sex differences were detected between the groups. However, in all regions the group that was excluded from the analysis was significantly older than the group that was included. Since current age of the child was significantly and inversely correlated with year of diagnosis in all regions, the children who were excluded from the analysis were more likely to have been diagnosed before 1997 and hence would not have met the inclusion criteria, or to have been diagnosed during the first three-year interval of the study period. Accordingly, the findings for 1997-1999 are where the greatest potential for bias exists.
While a discussion of diagnostic procedures over the study period is beyond the scope of this paper, it is probable that there were differences among regions as well as within each region over time in terms of the diagnostic criteria, types of professionals, and methods used to make the diagnosis. Regardless of how the diagnosis was made, however, early diagnosis is important for all the reasons mentioned in the introduction, and our findings suggest that children with autism are not being diagnosed at as young an age as the literature suggests they could be. Further study is warranted to understand the factors contributing to delays in diagnosis. Such research would inform best practices for early identification of autism and timely access to treatment and supports.
Acknowledgements: This work was supported by an Interdisciplinary Health Research Team Grant from the Canadian Institutes of Health Research (#43820) to the Autism Spectrum Disorders Canadian-American Research Consortium (ASD-CARC) (J.J.A. Holden, Principal Investigator) and an Operating Grant from the Canadian Institutes of Health Research (#79556) to H. Ouellette-Kuntz.
Received: May 9, 2008
Accepted: January 9, 2009
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Helene M.J. Ouellette-Kuntz, MSc,  Helen Coo, MSc,  Miu Lam, PhD,  C.T. Yu, PhD,  Marlene M. Breitenbach, MSEd,  Paula E. Hennessey, BA,  Jeanette J.A. Holden, PhD,  Hilary K. Brown, BA,  Andrea L. Noonan, MA,  Robert B. Gauthier, MEd, MSc,  Lori R. Crews, MSEd 
[1.] Associate Professor, Department of Community Health and Epidemiology, Queen's University, Kingston, ON
[2.] Research Associate, Department of Community Health and Epidemiology, Queen's University, Kingston, ON
[3.] Associate Professor, Department of Psychology, University of Manitoba, Winnipeg, MB
[4.] Special Education Autism Coordinator, Department of Education and Early Childhood Development, Charlottetown, PE
[5.] Provincial Consultant, Intervention Services & Autism, Department of Health & Community Services, St. John's, NL
[6.] Professor, Department of Psychiatry, Queen's University, Kingston, ON
[7.] Research Assistant, Department of Community Health and Epidemiology, Queen's University, Kingston, ON
[8.] Early Intervention Coordinator, Department of Social Services and Seniors, Charlottetown, PE
[9.] Professional Development Consultant, Department of Education, St. John's, NL
Correspondence and reprint requests: Prof. Helene Ouellette-Kuntz, Department of Community Health and Epidemiology, Queen's University, 191 Portsmouth Avenue, Kingston, ON K7M 8A6, Tel: 613-548-4417, Fax: 613-548-8135, E-mail: email@example.com
Table 1. Agencies in Manitoba, Southeastern Ontario, Prince Edward Island and Newfoundland and Labrador that Identify Children with an Autism Spectrum Disorder for the National Epidemiologic Database for the Study of Autism in Canada Region Agency Population Served Manitoba Children's Special All children under Services, Manitoba the age of 18, Department of with the exception Family Services & of children living Housing on reserves Southeastern Limestone District School-age children Ontario School Board Upper Canada District School-age children School Board Hastings & Prince School-age children Edward District School Board Algonquin & School-age children Lakeshore Catholic District School Board Catholic District School-age children School Board of Eastern Ontario Conseil des ecoles School-age children publiques de l'Est de l'Ontario Conseil des ecoles School-age children catholiques de langue francaise du Centre-Est Child Development All children under Centre, Hotel 18 years of age Dieu Hospital * living in Southeastern Ontario Pathways for Children 2-5 years Children & Youth, of age who have Autism Intervention been diagnosed Program or are considered end of the autism spectrum Prince Edward Department of Pre-school and Island Education and Early school-age children Childhood Development Newfoundland & Department of Education School-age children Labrador Department of Health and Children 18-84 months Community Services, of age with an autism Early Intensive spectrum disorder Intervention Services Region Method of Data Year Data Collection Collection Started Manitoba Agency staff review 2002 files and complete anonymized data collection forms for children under 18 years of age with an autism spectrum disorder Southeastern Agencies provide the 2003 Ontario research team with the date of birth and sex of all children under 15 years of age with an autism spectrum disorder, and send information letters and consent forms to their parents or legal guardians. If a consent form is sent back to the study team, more detailed demographic and diagnostic information is collected by telephone interview with the parent or legal guardian. Prince Edward Same as for 2002 Island Southeastern Ontario, except includes all children under 18 years of age with an autism spectrum disorder. Newfoundland & Same as for 2003 Labrador Southeastern Ontario * Referral and assessment centre for children with suspected developmental problems. Table 2. Median Age at First Diagnosis of an Autism Spectrum Disorder in Four Regions of Canada by Sex, Year of Initial Diagnosis and Diagnostic Subtype Manitoba n (%) Median Age, Months (IQ Range) Overall 505 (100.0) 48.0 (30.0) Sex Boys 421 (83.4) 47.0 (29.5) Girls 84 (16.6) 50.0 (37.5) p-value for intra-regional differences in median age at diagnosis by sex 0.217 Year of initial diagnosis 1997-1999 87 (17.2) 49.0 (24.0) 2000-2002 177 (35.0) 46.0 (30.0) 2003-2005 241 (47.7) 48.0 (35.5) p-value for intra-regional differences in median age at diagnosis by year of initial diagnosis 0.562 Diagnostic subtype Autistic disorder 183 (36.2) 42.0 (19.0) PDD-NOS 69 (13.7) 77.0 (55.5) Asperger's disorder 59 (11.7) 101.0 (65.0) ASD 194 (38.4) 42.0 (20.3) p-value for intra-regional differences in median age at diagnosis by diagnostic subtype <0.001 Southeastern Ontario n (%) Median Age, Months (IQ Range) Overall 117(100.0) 55.0 (51.5) Sex Boys 99 (84.6) 53.0 (48.0) Girls 18 (15.4) 64.0 (75.0) p-value for intra-regional differences in median age at diagnosis by sex 0.255 Year of initial diagnosis 1997-1999 26 (22.2) 43.0 (24.5) 2000-2002 45 (38.5) 58.0 (55.5) 2003-2005 46 (39.3) 61.5 (53.5) p-value for intra-regional differences in median age at diagnosis by year of initial diagnosis 0.004 Diagnostic subtype Autistic disorder 24 (20.5) 34.0 (27.3) PDD-NOS 25 (21.4) 59.0 (48.0) Asperger's disorder 29 (24.8) 89.0 (43.0) ASD 39 (33.3) 47.0 (20.0) p-value for intra-regional differences in median age at diagnosis by diagnostic subtype <0.001 Prince Edward Island n (%) Median Age, Months (IQ Range) Overall 56 (100.0) 47.5 (41.0) Sex Boys 46 (82.1) 45.0 (42.0) Girls 10 (17.9) 50.5 (72.3) p-value for intra-regional differences in median age at diagnosis by sex 0.171 Year of initial diagnosis 1997-1999 18 (32.1) 46.5 (35.8) 2000-2002 17 (30.4) 49.0 (46.5) 2003-2005 21 (37.5) 46.0 (64.5) p-value for intra-regional differences in median age at diagnosis by year of initial diagnosis 0.205 Diagnostic subtype Autistic disorder 11 (19.6) 44.0 (23.0) PDD-NOS 12 (21.4) 50.0 (41.8) Asperger's disorder 5 (8.9) 103.0 (40.5) ASD 28 (50.0) 44.5 (24.5) p-value for intra-regional differences in median age at diagnosis by diagnostic subtype 0.02 Newfoundland & Labrador n (%) Median Age, Months (IQ Range) Overall 91 (100.0) 39.0 (17.0) Sex Boys 78 (85.7) 39.0 (17.3) Girls 13 (14.3) 41.0 (18.0) p-value for intra-regional differences in median age at diagnosis by sex 0.905 Year of initial diagnosis 1997-1999 22 (24.2) 42.0 (17.3) 2000-2002 47 (51.6) 37.0 (24.0) 2003-2005 22 (24.2) 42.0 (14.5) p-value for intra-regional differences in median age at diagnosis by year of initial diagnosis 0.745 Diagnostic subtype Autistic disorder 27 (29.7) 40.0 (18.0) PDD-NOS 19 (20.9) * 48.0 (33.0) ([dagger]) Asperger's disorder - - ASD 45 (49.5) 36.0 (13.5) p-value for intra-regional differences in median age at diagnosis by diagnostic subtype 0.036 p-value for Inter-regional Differences in Median Age at Diagnosis Overall <0.001 Sex Boys <0.001 Girls 0.067 p-value for intra-regional differences in median age at diagnosis by sex Year of initial diagnosis 1997-1999 0.12 2000-2002 0.007 2003-2005 0.002 p-value for intra-regional differences in median age at diagnosis by year of initial diagnosis Diagnostic subtype Autistic disorder 0.206 PDD-NOS 0.001 Asperger's disorder 0.603 ASD 0.005 p-value for intra-regional differences in median age at diagnosis by diagnostic subtype Notes: The n denotes sample size used in the analysis, and does not reflect the total number of children diagnosed with an autism spectrum disorder for any of the categories listed. Percents are based on intra-regional totals. IQ = Interquartile, PDD-NOS = Pervasive developmental disorder, not otherwise specified, ASD = Autism spectrum disorder (non-specific diagnosis). * Due to small numbers, the Asperger's disorder and PDD-NOS categories were grouped together. ([dagger]) Values are for PDD-NOS only. Table 3. Median Age at First Diagnosis of an Autism Spectrum Disorder in Manitoba by Year of Diagnosis and Diagnostic Subtype Diagnostic Year of Initial Diagnosis of Subtype an Autism Spectrum Disorder 1997-1999 n Median Age, Months (IQ Range) Autistic disorder 28 44.0 (19.5) PDD-NOS 20 56.5 (47.8) Asperger's disorder 5 70.0 (54.0) ASD 34 43.5 (24.8) Diagnostic Year of Initial Diagnosis of Subtype an Autism Spectrum Disorder 2000-2002 n Median Age, Months (IQ Range) Autistic disorder 58 39.5 (15.5) PDD-NOS 20 75.0 (61.5) Asperger's disorder 23 74.0 (58.0) ASD 76 43.0 (18.3) Diagnostic Year of Initial Diagnosis of Subtype an Autism Spectrum Disorder 2003-2005 n Median Age, Months (IQ Range) Autistic disorder 97 42.0 (20.0) PDD-NOS 29 92.0 (51.5) Asperger's disorder 31 108.0 (59.0) ASD 84 41.0 (19.3) Diagnostic p-value Subtype Autistic disorder 0.651 PDD-NOS 0.021 Asperger's disorder 0.080 ASD 0.391 Notes: The n denotes sample size used in the analysis, and does not reflect the total number of children diagnosed with an autism spectrum disorder for any of the categories listed. IQ = Interquartile, PDD-NOS = Pervasive developmental disorder, not otherwise specified, ASD = Autism spectrum disorder (non-specific diagnosis).