Abstract â–¡ 70

Risk factors for Sudden Infant Death Syndrome (SIDS) parallel those for respiratory tract infections. Based on epidemiological and experimental work by our group and others, we suggested some SIDS deaths are due to pathophysiological responses elicited by combinations of microbial products and/or cigarette smoke during a developmental stage when infants' endocrine responses are less able to "damp down" the effects of inflammatory mediators. Laboratory investigations of infectious agents implicated in SIDS indicate developmental and environmental risk factors could affect 1) mucosal colonization of infants by potentially pathogenic bacteria and 2) induction and control of infants' inflammatory responses to infectious agents.

Exposure to cigarette smoke, viral infection and the prone sleeping position have been demonstrated to affect density and/or frequency of colonisation by bacterial species isolated from many SIDS infants at autopsy. The prone position also results in significantly higher temperatures in the nasal cavity which could contribute to induction of pyrogenic staphylococcal toxins identified in over half of SIDS infants examined in our recent study. The majority of these deaths occur at night; and studies on the inflammatory responses in relation to cortisol levels observed at night during different stages of development suggest these levels are not sufficient to control toxin induced pro-inflammatory responses such as tumour necrosis factor α and interleukin-6. New evidence suggests that there are genetic factors involved in the level of inflammatory responses to some bacterial antigens implicated in SIDS.

We suggest that further investigation of the role of infection and inflammation in relation to risk factors identified in epidemiological studies, particularly age incidence and maternal smoking, could provide important insights into: 1) mechanisms leading to death; 2) variability in the incidence of SIDS observed in different ethnic groups. This could provide significant information about the series of events leading to a fatal outcome and perhaps to new intervention schemes to reduce further the incidence of these deaths.