For the past couple of decades rates of autism seem to have risen dramatically but now a US Environmental Protection Agency (EPA) has pin-pointed a sudden jump in cases since 1988 and suspects yet to be identified environmental triggers are a likely explanation.
By reviewing extensive worldwide data EPA scientists were able to see that rather than a steady increase in the incidence of autism over a number of decades there was in fact a distinct "changepoint" in the 1988-1989 birth cohort - a sudden and substantial spike in autism rates.
Michael E. McDonald and John F. Paul, of the EPA's National Health and Environmental Effects Research Laboratory looked at specific Californian, Danish and worldwide datasets and found the same changepoint for autism incidence across all three. Acording to the researchers the rate of increase in new cases of autism before 1988 "was significantly different" than the rate after that year. In California, the rate spiked from 5.7-per-10,000 before the changepoint, to 20.8-per 10,000 after, while the worldwide dataset showed a similar jump - from 6.0 to 24.2. In Denmark, where autism had been extremely rare the rise was even more dramatic, going from 0.6 to 6.6 - total incidence remaining a fraction of that for California and worldwide however.