Editor—Recently, concerns about an apparent increase in the prevalence of autism in the general population, and the pathophysiology behind this, have been prominent in the press. Before these concerns can be addressed we need to be sure that the prevalence has truly increased. A cohort study was thought suitable to provide an insight into whether the prevalence of autistic disorders has increased.
In the British cohort 1970 study (BCS70) only five children were identified as having autism (and one as having suspected autism) at the age of 5 in disability data files. This gives a prevalence of 6/13 135 (0.45/1000)—comparable with that found in previous studies.1,2
A focus group consisting of practising consultants (from adult and paediatric disciplines) experienced in the diagnosis of autistic disorders was convened. This group identified several diagnostic features from the available data that they thought were important in making a diagnosis of autistic spectrum disorder. The aim was to identify whether there were missing or undiagnosed cases with current commonly used diagnostic features. The features identified from the original BCS70 questionnaire included:
At age 5RestlessSolitary; does things on ownFearful, afraid of new situationsFussy or over particular
At age 10Does things on own; rather solitaryAfraid of new situationsFussy or over particularHums or makes odd noisesObsessionalRequests must be met immediately
When an analogue scale was used, only the most extreme cases—that is, the top fifth—were identified. Cases in which the child had all features present at both age 5 and age 10 were then identified.
Using the methodology above, we identified 56 cases from 14 904 children studied at age 10, giving a prevalence of 3.76/1000. This suggests that these children have an autistic spectrum disorder when contemporary diagnostic features are used.
Our finding agrees with current lifetime prevalence figures suggested by Powell et al.3 Thus estimates of prevalence from the early 1970s may have seriously underestimated the prevalence at that time. Confirmation of this suggestion would require contemporary assessment of the individuals involved.
References
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