Objectives: (1) To investigate prevalence of ASC in
Methods: Study 1: A population-based count of known cases, using the Special Educational Needs (SEN) Register. Study 2: A population-based count of known cases, using direct parent report, via schools. Study 3: Schools in Cambridgeshire distributed the CAST (Childhood Autism Spectrum Test) to parents from Study 2. Face-to-face diagnostic assessments were conducted, using the ADI-R and ADOS, and undiagnosed cases were counted.
Results: Study 1: 79/96 mainstream schools participated (representing a population of 8,824 children aged 5-9 years) and reported 83 known cases of ASC, representing a prevalence estimate of 94 per 10,000. Study 2: 96/175 mainstream and special schools participated. 11,700 Diagnosis Surveys were sent to parents of children aged 5-9 years old. 3,373 were returned. Parents reported 41 existing diagnoses of ASC, representing a prevalence estimate of 99 per 10,000. Study 3: 3,373/11,700 parents returned the CAST. Known cases of ASC were excluded. 52 children scored ≥15 on the CAST and were assessed. Of these, 10 were given a research diagnosis of ASC. 25 children scored 12-14 on the CAST and were assessed. 1 was given a research diagnosis of ASC. The ratio of known-to-unknown cases is approximately 5:3.
Conclusions: The prevalence estimate of known cases of ASC, using different methods of ascertainment converges around 1%. The ratio of known to unknown cases means that for every three known cases there are another two unknown cases. This has implications for planning diagnostic, social and health services.