Neural tube defects in a country town. Conformation of clustering within a particularly small area.

Eighteen infants with neural tube defects occurring in 979 births over five years in a small Wiltshire town were investigated for evidence of spatial epidemicity. Applying a method not used previously in the study of these defects, clustering was confirmed, a critical distance between cases of up to 100 metres giving a highly significant result (P = 0·001), and with one exception the observed number of pairs significantly exceeds the expected number (P < 0·01) even up to 1,000 metres.