Weather temperatures and sudden infant death syndrome: a regional study over 22 years in New Zealand.

STUDY OBJECTIVE To examine and identify relationships between the sudden infant death syndrome (SIDS) and environmental temperature in Canterbury, New Zealand. DESIGN A retrospective epidemiological study combining details of regional hourly temperature and reported SIDS cases. SETTING Canterbury, New Zealand, between 1968 and 1989 inclusively. PARTICIPANTS All infants reported as dying from SIDS within the Canterbury region. MAIN RESULTS The SIDS incidence increased after months with prolonged colder minimum temperatures, confirming the seasonality of SIDS. After adjusting for this seasonality, days that showed little change in hourly temperature and days with warmer minimum temperatures recorded were seen to have a significantly increased the incidence of SIDS. No evidence was found for other relationships between the SIDS incidence and various measures of daily temperatures on the day of death, over the preceding eight days or between these days. Infants aged 12 weeks and over were more susceptible to SIDS on days when small hourly temperature changes were recorded than their younger counterparts; no other age differences emerged. CONCLUSIONS This study confirmed that the incidence of SIDS is affected by seasonality and temperature on the day of death. In particular, after a prolonged period of cold minimum temperatures, infants were most at risk from SIDS on days on which either a warmer minimum temperature or little hourly variation in temperature were recorded. No other daily or lagged daily temperature factor (lagged up to eight days before the day of death) was statistically associated with the SIDS incidence. It is suspected that the inconsistent previously published lag effect findings actually describe some other phenomenon such as parental behaviour or infant thermoregulation.