Recurrence incidence of sudden infant death syndrome.

The incidence of sudden infant death syndrome (SIDS) between birth and 2 years of age in South Australia was found to be 2.1/1000 live births. The incidence in previous siblings was 10 times that expected, in second degree relatives five times, and in third degree relatives four times that expected for the community. The minimum incidence in the next subsequent sibling was five times that expected. Except for one family in which both twins died during the same night, the surviving twin has never died (23 infants). The incidence of SIDS in adopted infants was similar to the incidence in natural born infants. Families in which two or more siblings died from SIDS differed from families in which only one infant died from SIDS in several ways. More infants were over 12 months old, and the mothers had an increased incidence of previous miscarriage and threatened miscarriage during the pregnancy with the infant who died. In one family both infants had bronchomalacia, and two families were severely socially deprived. For most families (92%) in which an infant died from SIDS the risk of recurrence is small (less that twice the expected risk). We have identified a small subgroup (8%) with a significantly increased risk of recurrence.