Infection cot death link probed
Common bacterial infections could be linked to some cases of unexplained cot death, research suggests.
The study, published in the Lancet, found samples from babies who had died for no apparent reason were more likely to carry potentially harmful bacteria.
Some scientists think bacterial toxins may affect breathing or nerve signals.
But the Great Ormond Street team which carried out the work said the findings did not alter current safety advice given to new parents.
There are around 250 sudden infant deaths a year in the UK, and although some can be proved to be due to an infection or other medical condition, the majority are never fully explained.
Scientists know that there are certain things that parents can do to cut the risk of cot death - such as not smoking during or after pregnancy, and putting babies to sleep on their backs, but the precise reasons why this helps are not completely understood.
The latest research does not prove that bacteria are responsible for any of these unexplained deaths, although it does, according to its authors, suggest a connection between the two.
The researchers took samples from 470 babies who had died suddenly, and tested them for the presence of bacteria, particularly those capable of causing illness, such as Staphylococcus aureus or E. coli.
In some cases, the cause of death was known to be a bacterial infection, or completely unrelated to infection, for example a heart defect or accident. The rest were entirely unexplained.
Among those known to have died from a bacterial infection, 24% of the bacteria found were potentially harmful, compared with only 11% of those found in the non-infection group.
However, among the "unexplained" group, the figure was 19%, with 16% of bacteria found in this group identified as Staphylococcus, compared with 9% in the non-infection group.
Professor Nigel Klein, one of the study authors, said there were three possible explanations for the difference - pure coincidence, a role for bacteria in causing the death, and the presence of bacteria being due to an unrelated factor which increased the risk of cot death.
He said: "We don't know which one of these is the case, and we certainly can't say at the moment that these bacteria are causing sudden infant death.
"However, it is possible that these bacteria may be more likely to be present in children who are exposed to other risk factors, such as smoking, so this research does reinforce the need for parents to follow existing advice on minimising the risk of cot death."
In a separate commentary in The Lancet, Dr James Morris and Dr Linda Harrison from Lancaster Royal Infirmary said that the study supported the idea that bacteria could be directly contributing to sudden death, perhaps as the poisons they produce interfere with breathing or nerve control.
Professor George Haycock, from the Foundation for the Study of Infant Deaths, said that while bacteria could kill by causing overwhelming infections, such as meningococcal septicaemia, there were studies which suggested that some babies were better suited to dealing with less obvious infections.
"Several studies, some of them funded by us, suggest that small genetic variations in the chemicals that control the inflammatory response to infections and to exposure to toxins may cause some infants to have an exaggerated, possibly overwhelming, inflammatory reaction whereas others might experience little or no disturbance."