The changing epidemiology of SIDS.

Within the past five years, the number of deaths attributed to the sudden infant death syndrome (SIDS) has fallen dramatically in the UK,' 2 New Zealand,3 Australia,4 the Netherlands,5 Norway,6 Denmark,7 and Ireland.8 In England and Wales, the number of SIDS victims has fallen by nearly 70% from 1593 in 1988 to 531 in 19921 (see table 1). The decline has coincided with public health advice to avoid the prone sleeping position but other risk factors may have also changed. The contribution of any one risk factor to the fall in SIDS incidence depends on the associated relative risk for SIDS, the prevalence ofthe factor in the young infant population, and the change in prevalence. Consistent associations have been established between SIDS and male sex, intrauterine growth retardation, preterm birth, poor socioeconomic status, young maternal age, multiple birth, and short interpregnancy interval.911 However, the prevalence of these factors changes little from year to year. The prevalence of some environmental factors is more variable. Of these, the prone sleeping position and maternal smoking have been most consistently associated with SIDS, whereas evidence for a role for heavy wrapping, infection, bottle feeding, or bed sharing is less clear. This paper examines the potential contribution of specific environmental risk factors to the fall in SIDS incidence.