A Multi-Site Study of Prevalence, Incidence, and Age at First Diagnosis for Autism Spectrum Disorders: Findings from the Mental Health Research Network Autism Registry Study
Reported prevalence of autism spectrum disorders (ASDs) in the US has increased from 0.45/1000 children in the 1960s to approximately 11.3/1000 in 2008. Prevalence statistics vary greatly depending on study methodology and demographics of the populations.
The objective of this study was to pool data from several large health systems across the US to investigate trends in ASD prevalence, incidence, and age at first diagnosis from 1997-2010, and to assess variation in trends across demographic factors.
Children born between January 1, 1993 and December 31, 2008 and members of one of five health plans in the Mental Health Research Network Autism Registry project were included: Kaiser Permanente (KP) Northern California, KP Northwest, KP Southern California, KP Southeast, and Harvard Pilgrim Health Care. Children with an ASD diagnosis from an ASD specialist or two or more ASD diagnoses from non-specialists recorded in medical records were considered to have ASD. Annual prevalence was based on individuals with any health plan membership in that particular year. Annual cumulative incidence and median age at first diagnosis were calculated for each birth year cohort and included children with 6 or more months of membership in each year of life (with the exception of the first year after birth).
We identified a total of 24,062 children with ASD among a total pediatric population of 3,938,603 born in the study years. Among children aged 5-9 years in a given year, prevalence of all ASDs increased steadily from 1.5/1000 in 1998 to 12.0/1000 in 2010 with similar increases in Autistic Disorder or AD (1998: 1.0/1000, 2010: 8.5/1,000) and non-AD ASD (1998: 0.5/1000, 2010: 3.4/1000).
Prevalence of all ASDs in children aged 5-9 years in 2010 varied by race/ethnicity (White: 20.1/1000, Black: 15.6/1000, Asian: 17.2/1000, Hispanic: 14.0/1000). Prevalence of ASDs among males aged 5-9 years was higher than among females (2010: males = 23.8/1000, females = 5.5/1000).
Incidence of all ASDs before age 6 increased steadily (1997 Birth Cohort: 4.8/1000, 2005 Birth Cohort: 12.2/1000), as did incidence of AD (1997: 3.7/1000, 2005: 9.0/1000) and non-AD ASD (1997: 1.1/1000, 2005: 3.1/1000). Median age of first diagnosis among children aged 5 or lower fell from 4.77 for children born in 1996 to 3.07 for 2005 births. Median age at first diagnosis for 2005 births did not vary much by race/ethnicity (Blacks: 3.07, Asians: 3.01, Hispanics: 3.10, Whites: 3.02).
This study provides up-to-date prevalence and incidence information from several large, diverse, and health-insured populations. Prevalence and incidence of ASDs and ASD subtypes increased over the years while median age of diagnosis fell. Differences in results across race/ethnic groups require further exploration.