Sudden infant death syndrome: does winter affect poor and rich babies equally?

STUDY OBJECTIVE The aim was to investigate whether the winter increase in risk of sudden infant death was similar across social classes. DESIGN This was an unmatched case-control study using routine data. SETTING Cases and controls were selected from files holding routine birth and death certificate data for England and Wales for 1986. SUBJECTS Cases were deaths in the first year of life occurring in the summer or the winter of 1986 with mention of sudden infant death or SIDS in the death certificate. Controls were a 1% random sample of all children born in the same year. Only children whose parents were married or living together at the time of birth registration were included. MAIN RESULTS Data on age and season of death for cases, and on date of birth, social class of father, and birth weight were abstracted from the file. Season of birth and birth weight were treated as confounding variables. The increase in risk of SIDS in winter was calculated for each age group and social class. The winter increase in SIDS was more marked among the higher social classes for all ages, but not to a statistically significant degree: the p values for heterogeneity were 0.26 for age 0-3 months, 0.42 for 4-7 months, and 0.41 for 8-12 months. CONCLUSIONS There is no direct association between seasonal variation in sudden infant death and social class.