Epidemiology of infantile autism in southern Ibaraki, Japan: differences in prevalence in birth cohorts.

Researchers counted every child born in southern Ibaraki, Japan between 1972 and 1978 who met DSM-III rules for autism.

They used school and clinic records to find cases, then looked for seasonal patterns and four-year cycles in the numbers.

The team found 1.4 cases of autism for every 1,000 children.

Odd peaks lined up with winter pneumonia hospital admissions in four-year cycles, hinting that winter illness and autism counts rose and fell together.

Matson et al. (2013) looked deeper into the same age band and showed that a toddler’s developmental level only slightly softens autism signs. This moves the story from “how many” to “how symptoms look” in kids already counted.

Hudry et al. (2014) followed high-risk babies and found that a fading receptive-vocabulary edge at 14 months flags later ASD. Together with the 1988 snapshot, we now see both early warning signs and final counts.

Reyes et al. (2019) later showed that temperament traits in preschoolers with ASD shift more over time than in typical kids. This warns us that the static prevalence picture from 1988 can hide moving targets—kids change, so reassess.

You now have a historical yardstick: 1.4 per 1,000 in the 1980s. When families ask “how common is autism?” you can share the number and note that winter illness cycles once tracked with it. More important, the later papers tell you to watch early language dips and to recheck temperament over time, not just at intake.