Diagnostic and assessment issues in autism surveillance and prevalence

The purpose of this paper is to provide a review of the results of published epidemiological surveys of the prevalence of pervasive developmental disorders (PDD) between 1966 and 2010(61 studies). Recent survey estimates suggest that the rate for autistic disorder is about 22/10,000 and that for all forms of PDD is around 70/10,000. Prevalence rates have increased over time in most countries. A discussion of the possible interpretations of time trends in prevalence estimates is also provided. The recent, upward trend in the rates of PDD is likely explained, at least in part, by changes in case definition and identification, public awareness, social services and policies, and study design variables. True changes in the underlying incidence of PDDs cannot nevertheless be ruled out. Surveillance of epidemiological trends in PDD incidence is required in future years.