Bacteria and SIDS 

The research group carried out a systematic retrospective case review of autopsies, done at one specialist centre between 1996 and 2005, of 546 infants (aged 7-365 days) who died suddenly and unexpectedly. Cases of SUDI were categorised as unexplained, explained with histological evidence of bacterial infection, or explained by non-infective causes. Microbial isolates gathered at autopsy were classified as non-pathogens, group 1 pathogens (organisms usually associated with an identifiable focus of infection), or group 2 pathogens (organisms known to cause septicaemia without an obvious focus of infection).

Significantly more isolates from infants whose deaths were explained by bacterial infection and from those whose death was unexplained contained group 2 pathogens than did those from infants whose death was explained by a non-infective cause. Significantly more cultures from infants whose deaths were unexplained contained Staphylococcus aureus than did those from infants whose deaths were of non-infective cause.

Although many post-mortem bacteriological cultures in SUDI yield organisms, most seem to be unrelated to the cause of death. The high rate of detection of group 2 pathogens, particularly S aureus and E coli, in otherwise unexplained cases of SUDI suggests that these bacteria could be associated with this condition.

Recent research by Dr David Drucker (2) and Professor Caroline Blackwell, (3) also funded by FSID, supports this theory. The work of Highet (4) also sits well with these findings. This study showed how findings at post mortem are consistently similar to the origin and development of toxaemic shock and/or sepsis. Also, the major risk factors for SIDS parallel those for increased colonization and serious bacterial infections and the natural variation in the incidence of SIDS cases is typical of an infectious disease.

We have been aware of the common bacterial hypothesis (5) of sudden and unexpected infant deaths for more than 20 years. Yet these new findings are interesting and important and we are looking forward to more studies in this area.

Sophie Bissmire, a bereaved parent comments on this resaerch:
“My daughter Neave died suddenly and unexpectedly while at home with my husband. All we wanted was to know why so when the PM results showed that Neave had died with Overwhelming Staph.A. infection it allowed us to stop feeling so guilty, especially my husband who was blaming himself for no reason. So, although parents won't be able to find out more about why their babies died it is really valuable in piecing together the heartbreaking puzzle of cot death.”

References:
1 Weber MA, Klein NJ, Hartley JC, et al. Infection and sudden unexpected death in infancy: a systematic retrospective case review. Lancet 2008;371(9627):1848-53.
2 Dashash M, Pravica V, Hutchinson IV, et al. Association of sudden infant death syndrome with VEGF and IL-6 gene polymorphisms. Hum Immunol 2006;67(8):627-33.
3 Blackwell C. Infection, inflammation and SIDS. FEMS Immunol Med Microbiol 2004;42(1):1-2.
4 Highet AR. An infectious aetiology of sudden infant death syndrome. J Appl Microbiol 2008.
5 Morris JA, Haran D, Smith A. Hypothesis: common bacterial toxins are a possible cause of the sudden infant death syndrome. Med Hypotheses 1987;22(2):211-22.