Sudden infant death syndrome: Seasonality and a biphasic model of pathogenesis

Abstract

Study objective-This paper examines the relationship between season, age, and the sudden infant death syndrome (SIDS). It provides a theoretical model for the pathogenesis of SIDS and uses it as a framework to consider risk factor mechanism. Design-A case series analysis was used to examine season and age in relation to SIDS and seasonal pattern and age at death distribution of perinatal risk factors. Setting-The source population for the SIDS cases in this study was all live births in the state of Tasmania, Australia, 1975 to 1987 inclusive. Subjects-Cases were all infants born 1975 to 1987 who died of SIDS on whom birth notification information was available (n = 348). The live birth cohort 1980-87 (n = 55,944) was used as the control population for risk factor identification. Measurements and main results-The median ages of death for spring, summer, autumn, and winter born infants were 115, 103.5, 91 and 78 days. Spring and summer born infants died at a significantly older median age than winter born infants. The month of birth distribution of SIDS cases did not alter significantly from a uniform, nonseasonal distribution (p > 0.25) but month of death was seasonally distributed (p < 0.01). Premature and low birthweight infants died at an older median age (p < 0.05) than term and non-low-birthweight infants. An excess of male infant deaths and infant deaths to older mothers occurred during winter (P < 0.05). Conclusions-The pathogenesis of SIDS can be represented as a biphasic model with three pathways of risk factor operation. In this study, season influenced the age at death of SIDS infants. We propose that risk factors with a strong seasonal distribution are likely to be operating in the postnatal period.