Outdoor carbon monoxide, nitrogen dioxide, and sudden infant death syndrome.

AIMS To investigate whether infants who died of SIDS were more likely to have higher acute and lifetime average exposures to outdoor carbon monoxide (CO) and nitrogen dioxide (NO2) than comparison healthy infants. METHODS A total of 169 case and 169 matched control infants born between 1988 and 1992, were studied. CO and NO2 concentrations, averaged for all days within the infant's lifespan, and the last 30 days, 7 days, 3 days, and 1 day of life were obtained from air pollutant data provided by the California Air Resources Board. RESULTS Based on monthly aggregated data, average CO and particularly NO2 were associated with SIDS count, even after adjustment for seasonal trends. SIDS outcome was not significantly associated with high average outdoor CO levels for any time period. However, high average outdoor NO2 levels on the last day of the infant's exposure period were significantly associated with SIDS; the adjusted odds ratio was 2.34 (95% CI 1.13 to 4.87). CONCLUSIONS SIDS may be related to high levels of acute outdoor NO2 exposure during the last day of life. Further studies are needed to replicate this finding.