The number of newly diagnosed cases of autism has levelled off in the UK after a five-fold surge during the 1990s, finds research published in the online journal BMJ Open.
The findings differ from widely publicised results issued by the US
Centers for Disease Control and Prevention (CDC) last year, which
reported a 78% increase in the prevalence of the condition in eight year
old children between 2004 and 2008 in the US.
Prompted by these data, which found that one in every 88 eight year
old children in the US had been diagnosed with an autistic spectrum
disorder in or before 2008, the authors wanted to find out if there were
comparable rates in the UK.
They used entries into the General Practice Research Database (GPRD),
which contains around three million anonymised active patient records
from over 300 representative general practices in the
5% of the UK population.
Data from practices enrolled from 1990, when the GPRD was set up,
were used to calculate the annual prevalence (number of people living
with the condition) and the annual incidence (number of newly diagnosed
cases) of autistic spectrum disorders among eight year olds, all of whom
were born after 1996.
Annual prevalence rates for 2004-2010 were calculated by dividing the
number of eight year olds diagnosed as autistic in that or any previous
year, by the number of eight year olds enrolled in the database for
Annual incidence rates were calculated by dividing the number of
eight year olds who had been newly diagnosed with autism between 2004
and 2010 by the number of eight year olds enrolled into the database for
each of those years.
The results showed that the annual prevalence and incidence of autism
did not materially change over the entire study period, for either boys
The annual prevalence of autistic spectrum disorders was estimated at
3.8 per 1000 boys and 0.8 per 1000 girls, while the annual incidence
was estimated at 1.2 per 1000 boys (1190 in total) and 0.2 per 1000
girls (217 in total).
Girls were about 75% less likely to be diagnosed with an autism spectrum disorder as boys.
The UK prevalence of about 4/1000 children is substantially lower
than the equivalent US figure of about 11/1000 children in 2008, which
was reported in 2012.
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