[Sudden infant death. Epidemiological factors in unexplained, partially or insufficiently explained causes of death].

Epidemiologic investigations were carried out on 185 infants, who died suddenly and on whom autopsies were performed. 53 infants died a "true sudden infant death", for 90 infants death was partly, and for 42 death was adequately explained. The three groups of SID infants were concordant with regard to the following parameters: the peak of mortality was found at about three months of age; among the SID probands, first born were less, third and later born were more numerous than in the general population; mothers of first, second and third born SID probands were younger as compared to the general population; SID probands were born twice as often in October as in March. Differences between children of Swiss or foreign parentage respectively were of minor significance with relatively few illegitimate and relatively many foster children among the foreign SID probands. 185 diseased children who had died in hospital and on whom autopsies were performed served as one control group; a second control group consisted of 1020 unselected newborns of the city of Zurich. The test groups resembled one another in their deviation from the controls and thus seem to form an entity distinct from non-SID infants.