Interactions of infectious symptoms and modifiable risk factors in sudden infant death syndrome. The Nordic Epidemiological SIDS study

The aim of the study was to investigate the effect of infection on sudden i nfant death syndrome (SIDS) and to analyse whether modifiable risk factors of SIDS, prone sleeping, covered head and smoking act as effect modifiers. In a consecutive multicentre case-control study of SIDS in Denmark, Norway and Sweden, questionnaires on potential risk factors for SIDS were complete d by parents of SIDS victims, and for at least two controls matched for gen der, age and place of birth. All SIDS cases were verified by an autopsy. Th e study comprised 244 SIDS cases and 869 controls, analysed by conditional logistic regression. Significantly more cases than controls presenting symp toms of infectious diseases during the last week and/or last day were treat ed with antibiotics and had been seen by a physician. The finding is consis tent with the hypothesis of an infectious mechanism in SIDS induced by loca l microorganism growth and toxin or cytokine production, and also adds furt her support to a possible association between infection and SIBS by loss of protective mechanisms, such as arousal. The risk of SIDS among infants wit h the combined presence of infectious symptoms and either of the other modf iable risk factors, prone sleeping, head covered or parental smoking. was f ar greater than the sum of each individual factor. These risk factors thus modify the dangerousness of infection in infancy.