Is short-term exposure to low and high ambient temperatures associated with an increased risk of sudden unexpected death in infancy? A case-crossover study in France (2015-2022)

BACKGROUND: Sudden unexpected death in infancy (SUDI) is a leading cause of infant mortality. Although ambient temperature affects many health outcomes, evidence on its association with SUDI remains limited. We examined short-term effects of high and low temperatures on SUDI in France. METHODS: We performed a time-stratified case-crossover study including lag periods up to six days before death. Conditional logistic regression models assessed associations with both binary temperature indicators (based on percentiles) and continuous metrics using a distributed lag nonlinear model (DLNM). Effect modification by season, sex, social deprivation, urban or rural residence, age at death, and sleeping position was examined. RESULTS: We included 1078 SUDI cases in France from 2015 to 2022. Results suggested an increased risk with heat on days close to death. Estimates were imprecise due to the limited sample size, leading to wide confidence intervals for several associations. However, we observed a linear association between temperature and SUDI during summer, particularly for minimum temperature in the last week of life (OR: 1.16, 1.07-1.26). DLNM analyses suggested similar patterns, with elevated risk for minimum temperatures above 15 °C and below 0 °C, though these estimates remain uncertainty. CONCLUSIONS: Short-term exposure to both high and low temperatures showed patterns of association with SUDI, with particularly notable effects of heat during summer. Although statistical support for many trends was limited, the alignment of these signals with previous studies suggests that preventive measures to reduce temperature-related risks for infants may be considered, particularly in the context of rising temperatures.