The ASDEU autism prevalence study in northern Spain.

: The prevalence of autism spectrum disorders (ASD) was studied in children in the County of Gipuzkoa (Basque Country, Spain) as part of the European Union's Autism Spectrum Disorder in Europe project (ASDEU-https://asdeu.eu). To identify cases in a total community sample of 7- to 9-year-old pupils (N = 14,734), a multistage approach was adopted: in the first stage, a teacher nomination (TN) form was completed by school teachers; and in the second stage, all families with a child nominated by their teachers were invited to complete the Social Communication Questionnaire (SCQ). A total of 108 (59%) schools participated fully, yielding a final sample of 9177 of 14.734 (61.9%) pupils. A total of 212 (2.3%) children were nominated via the TN form, and of these, 105 (49.5%) returned the completed SCQ. Twenty-five (23.8%) cases with SCQ scores ≥ 15 were invited to undergo a free clinical assessment, and 10 (40%) new cases of ASD were identified. The prevalence estimate included the 55 cases already being supported by the Gipuzkoa's only ASD association, the Gipuzkoa Autism Society (Asociacion Guipuzcoana de Autismo/GAUTENA)), as well as the 10 new subjects identified by the ASDEU field diagnostic process. A sensitivity analysis was performed to estimate new potential ASD cases among the non-participant schools, leading to a final figure of 87 cases of ASD in this age-bracket at the date of the study. This global probabilistic estimate, including non-participating schools, would thus provide a population prevalence of 0.59% (95% CI 0.48-0.73), a result lower than those reported by some other studies. Attrition rates in cross-sectional studies are challenging and support the need for developing longitudinal ASD incidence surveillance study areas (ASD observatories).