Air Pollution and Sudden Infant Death Syndrome

Background. Sudden infant death syndrome (SIDS) affects 1 in 1000 live births and is the most common cause of infant death after the perinatal period. Objective. To determine the influence of air pollution on the incidence of SIDS. Methods. Time-series analyses were performed to compare the daily mortality rates for SIDS and the daily air pollution concentrations in each of 12 Canadian cities during the period of 1984-1999. Serial autocorrelation was controlled for by city, and then the city-specific estimates were pooled. Increased daily rates of SIDS were associated with increases, on the previous day, in the levels of sulfur dioxide (SO2), nitrogen dioxide (NO2), and carbon monoxide but not ozone or fine particles measured every sixth day. Effects persisted despite adjustments for season alone or the combination of daily mean temperature, relative humidity, and changes in barometric pressure for NO2 and SO2 but not carbon monoxide. Results. Increases in both SO2 and NO2, equivalent to their interquartile ranges, were associated with a 17.72% increase in SIDS incidence. Conclusion. Ambient SO2 and NO2 may be important risk factors for SIDS. Pediatrics 2004;113:e628–e631. URL: http://www.pediatrics.org/cgi/content/full/113/6/e628; air pollution, epidemiology, SIDS. ABBREVIATIONS. SIDS, sudden infant death syndrome; PM10, particulate matter with a median aerodynamic diameter of 10 m. The rate of sudden infant death syndrome (SIDS) in the mid-1990s was 1 in 1000 live births.1,2 In Canada, the incidence of SIDS decreased from 1.09 in 1000 live births in 1984 to 0.49 in 1000 live births in 1999. Many risk factors have been identified and publicized, including the winter season,2,3 lower social status of parents,4 environmental tobacco smoke,1,4 and the prone position.2 The role of ambient air pollution has received little attention, is controversial,3,5,6 and is not often considered in epidemiologic studies and reviews of SIDS.1,2,4 One reason why the influence of air pollution on SIDS has received relatively little attention is related to the challenging methodologic issues involved. Similar to the studies that documented the currently accepted risk factors for SIDS, air pollution studies must be observational and not interventional. Large populations must be studied because of the relatively infrequent event rate and the expected modest effect size of air pollution. Administrative database studies comparing regional mortality statistics and regional air pollution concentrations and case-control designs are efficient for the study of infrequent events but are prone to confounding. If the rates of SIDS in areas with high levels of pollution were compared with the rates in areas with lower levels, then it would be necessary to control for the many other potential personal risk factors for SIDS that may differ according to region to avoid potential confounding. To investigate the influence of ambient air pollution on SIDS, we conducted a time-series analysis comparing daily rates of SIDS and daily concentrations of air pollution during a 16-year period in Canada. A large, unbiased population sample was studied. Social status and the many other risk factors mentioned above required no adjustment, because we compared mortality rates on higher– and lower– air pollution days for the same population. To bias the results, a variable would need to be associated with daily changes in air pollution and also be a risk factor for SIDS, making confounding unlikely.