COMMENTARY

Currently, there are few data about the prevalence of autism and related disorders (hereafter autism) in the United States. This study was conducted within the context of ongoing surveillance of autism, recently initiated through the Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP) of the US Centers for Disease Control and Prevention. The authors should be commended for their careful attempt to identify cases within the context of existing records and to document demographic and other characteristics associated with autism. This is the largest cohort reported to date. The authors address several important issues, including whether the prevalence of autism differs by race, and the sources through which cases were most likely to be identified.

As the authors note, the identification of cases is limited by the methods employed. Cases were identified through expert review of abstracted educational and medical or other diagnostic records, pre-selected for either a diagnosis or suspicion of autism, or for special educational services or placement. There was no independent evaluation of possible cases, nor any validation of cases included or excluded (ie children whose records implicated other, non-autistic disorders or problems). The majority of identified cases had been previously diagnosed with autism (62%), or autism had been suspected (19%). It is therefore unsurprising that the prevalence estimate is lower than that reported in recent studies using independent and standardised methods of diagnosis. For instance, Chakrabarti and Fombonne reported prevalence of 6 to 7 per 1000.¹

The data reported by Yeargin-Allsopp et al might be more accurately viewed as representing current diagnostic and educational service rates for autism. As would be expected based on this view, the data suggest that rates are lower in younger children, some of whom have yet to be diagnosed, and in older children, who may have been diagnosed using a more restrictive definition of autism.

Evidence of cognitive impairment in the majority (68%) of identified cases suggests that diagnostic and service rates are not currently capturing the relatively large, more cognitively capable subgroup with autism. Another potentially important finding is the less frequent use of medical and diagnostic services by black families and less educated mothers. This raises concern about the possibility of differential access to appropriate services. It might also be important to assess whether the mean age at diagnosis (3.9 years) changes over time, particularly given evidence of the effectiveness of early autism-specific intervention.² MADDSP provides a rich population-based database on autism that appears particularly well suited to addressing these and related diagnostic and service issues.