Though SIDS is the third leading cause of death among babies before their first birthday, its cause or causes remain a mystery.
Interventions designed to reduce known risk factors for sudden infant death syndrome, such as putting babies to sleep on their backs or convincing moms to stop smoking, are credited with lowering SIDS deaths by more than 50% in the U.S. between the mid- and late-1990s.
But no one really understands why the interventions work, SIDS researcher James A. Morris, MD, of the Royal Infirmary Lancaster, tells WebMD.
"We told people to do this, but we couldn't tell them why," he says.
Bacterial Infection and SIDS
The new research explored the old idea that bacterial infection is to blame for at least some cases of sudden, unexplained death among babies.
Pediatric pathologist Neil J. Sebire, MD, and colleagues from London's Great Ormond Street Hospital for Children reviewed the autopsy results of close to 500 babies who died suddenly and unexpectedly.
The researchers grouped the cases by whether the autopsies revealed no obvious cause of death, evidence of bacterial infection as a likely cause, or evidence of another cause that was not bacterial.
Bacterial samples taken at autopsy were also grouped by whether the bacteria were associated with obvious causes of death by infection or whether the bacteria could cause rapid death without an obvious infection.
Two bacteria in the latter group -- Staphylococcus aureus and Escherichia coli -- were found to be more common than expected in babies whose deaths could not be explained.
Sixteen percent of samples from infants whose deaths remained unexplained after autopsy contained the staph bacteria, compared with 9% of infants whose deaths were explained but not related to infection. And 6% of samples from the former group contained E. coli, compared with just 1% of samples from the latter.
The study and an editorial by Morris and colleague Linda Harrison, MD, appear in the May 30 issue of The Lancet.
Are Toxins to Blame?
Morris and Harrison write that the findings could help explain why SIDS deaths happen so quickly, with the transition from apparent good health to death often occurring in less than an hour.
"The only way to imagine that this could occur is by the release of bacterial toxins into the bloodstream," Morris tells WebMD.
The new study does not prove that the bacterial toxins play a role in SIDS, but it adds to a compelling body of research supporting the link, Morris says.
This research includes his own 1999 investigation showing heavier growths of S. aureus and E. coli in nasal samples from babies who slept on their stomachs, compared with babies who slept on their backs.
"If bacterial toxins are responsible for SIDS, this would explain why [back sleeping] improves survival," he says.
Morris adds that the relatively new science of proteomics, which examines how proteins impact disease, could help solve the mystery of SIDS.
"The next step is not just to look for the bacteria in these babies, but to look for the toxins that the bacteria are producing," he says. "That is where this new science comes in."