Toxigenic bacteria and sudden infant death syndrome (SIDS): nasopharyngeal flora during the first year of life.

Many developmental and environmental risk factors for sudden infant death syndrome (SIDS) are similar to those for susceptibility to respiratory tract infection, and toxigenic bacteria have been implicated in some SIDS cases. We assessed nasopharyngeal flora of healthy infants in relation to risk factors to determine which species best lit the mathematical model proposed for the common bacterial toxin hypothesis and if these findings complemented results obtained from SIDS cases which occurred during the period of the survey. Longitudinal studies were carried out between April 1993 and March 1996 on 253 healthy infants and their mothers. 150 from a multiply deprived area, 103 from an affluent area. Concurrent SIDS infants (37) were screened for nasopharyngeal flora. Among healthy infants < or = 3 months of age, the predominant isolate was Staphylococcus aureus 57% compared with 86% for SIDS infants in that age range (P< 0.02). There were significant associations between isolation of different species from both mother and baby but no association between isolation of any species with: area of residence: parental smoking habits; breast or bottle feeding; symptoms of viral infection: seasonality. We conclude that S. aureus fits the mathematical model for SIDS. Both staphylococci and/or their toxins were identified in a significant proportion of SIDS cases. Isolation of staphylococci from healthy infants was associated with the 2-4-month age range, a risk factor consistently found in all epidemiological studies of SIDS. This might reflect the developmental stage in which 80-90% of infants express the Lewis(a) antigen which we have shown to be one of the receptors for S. aureus.