Background: Climate change may lead to more severe and extreme heat waves in the future, but its potential impact on sudden infant death—a leading cause of infant mortality—is unclear.

Objectives: We sought to determine whether risk of sudden infant death syndrome (SIDS) is elevated during hot weather.

Methods: We undertook a case-crossover analysis of all sudden infant deaths during warm periods in metropolitan Montreal, Quebec, Canada, from 1981 through 2010. Our analysis included a total of 196 certified cases of SIDS, including 89 deaths at 1–2 months of age, and 94 at 3–12 months. We estimated associations between maximum outdoor temperatures and SIDS by comparing outdoor temperatures on the day of or day before a SIDS event with temperatures on control days during the same month, using cubic splines to model temperature and adjusting for relative humidity.

Results: Maximum daily temperatures of ≥ 29°C on the same day were associated with 2.78 times greater odds of sudden infant death relative to 20°C (95% CI: 1.64, 4.70). The likelihood of sudden death increased steadily with higher temperature. Associations were stronger for infants 3–12 months of age than for infants 1–2 months of age, with odds ratios of 3.90 (95% CI: 1.87, 8.13) and 1.73 (95% CI: 0.80, 3.73), respectively, for 29°C compared with 20°C on the day of the event.

Conclusions: High ambient temperature may be a novel risk factor for SIDS, especially at ≥ 3 months of age. Climate change and the higher temperatures that result may account for a potentially greater proportion of sudden infant deaths in the future.

Citation: Auger N, Fraser WD, Smargiassi A, Kosatsky T. 2015. Ambient heat and sudden infant death: a case-crossover study spanning 30 years in Montreal, Canada. Environ Health Perspect 123:712–716;  http://dx.doi.org/10.1289/ehp.1307960

Address correspondence to N. Auger, Institut national de santé publique du Québec, 190, boulevard Crémazie Est, Montréal, Québec, H2P 1E2, Canada. Telephone: 1-514-864-1600, ext. 3717. E-mail: nathalie.auger@inspq.qc.ca

This study was funded by a grant from the Fonds de Recherche du Québec-Santé. N.A. acknowledges a career award from the Fonds de Recherche du Québec-Santé.

The funding agencies were not involved in the design and conduct of the study; the collection, management, analysis, and interpretation of the data; the preparation, review, or approval of the manuscript.

The authors declare they have no actual or potential competing financial interests.

Received: 4 December 2013 Accepted: 4 March 2015 Advance Publication: 6 March 2015 Final Publication: 1 July 2015

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