Researchers have pinpointed two common bacteria that may contribute to sudden infant death syndrome, or SIDS, even when infants show no sign of tissue damage.
Postmortem tests on more than 500 babies found high levels of Staphylococcus aureus and Escherichia coli in babies who died for unexplained reasons, a team from Great Ormond Street Hospital for Children in London reported today in the journal Lancet.
One explanation could be that the bacteria release deadly toxins that damage the young heart, lungs or nervous system.
But bacterial growth may also aggravate or be a secondary effect of other known risk factors, such as overheating, parental smoking and lying a child on his or her stomach.
SIDS is a leading cause of death in babies younger than a year old, yet its root cause remains a mystery.
The latest findings suggest that underlying infection could be an important component.
"You've got to be very careful how you interpret this data," said Nigel Klein, one of the researchers. "But we did find an increased number of bacteria grown from particularly the lungs and spleen in infants who died unexpectedly without a known cause."
Cases of S. aureus and E. coli infections were significantly more frequent in the group of babies with unexplained deaths than in those who died of non-infective explained causes, such as congenital abnormalities.
Alan Craft, professor of child health at the University of Newcastle, said that the findings were important but that there might not be a simple answer. "The bacteria found are ones which are in all of our bodies most of the time," he said.