Babies should sleep on their backs
Some cases of cot death may be due to a bacterial infection, researchers say.
The Archives of Disease in Childhood study found samples from babies who had died for no apparent reason often carried potentially-harmful bacteria.
Some experts believe toxins produced by these bacteria could trigger a chemical storm, which overwhelms the baby, resulting in sudden death.
There are around 250 sudden infant deaths a year in the UK. The majority are never fully explained.
REDUCE COT DEATH RISK
Place your baby on their back to sleep
Do not let anyone smoke in the same room as your baby
Do not let your baby get too hot or too cold
Keep baby's head uncovered - place your baby with their feet to the foot of the cot
Do not share a bed with your baby if you have been drinking alcohol, take drugs or if you are a smoker
If your baby is unwell, seek medical advice promptly
The safest place for your baby to sleep is in a cot in a room with you for the first six months
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.
Associate professor Paul Goldwater, from The Women's and Children's Hospital and the University of Adelaide in Australia, who carried out the latest research, believes bacterial infections may contribute to some sudden infant deaths.
He analysed the post mortem reports for 130 babies who had died of sudden infant death syndrome (SIDS), 32 who had died suddenly as a result of infection, and 33 who had died of non-infectious cause, such as a road traffic accident.
He then analysed the bacterial isolates from "sterile" sites which are normally free of infections, such as heart blood, spleen, or cerebrospinal fluid, in the SIDS babies, and compared these with those of the other 65 babies.
Infection at a sterile site was rare in those infants who had died of non-infectious causes, but this was relatively common in both the SIDS babies and the babies who had died suddenly as a result of infection.
Unsurprisingly, almost one in five of the babies who had died suddenly as a result of infection had a sterile site infection. But so too did one in 10 of the SIDS babies.
In many cases, the infection was caused by Staphylococcus aureus, a particularly virulent bacteria, known to produce potentially lethal toxins.
Dr Goldwater told Archives of Disease in Childhood: "The finding of S. aureus in a normally sterile site in a large proportion of cases of SIDS would indicate that a proportion of these babies died of staphylococcal disease."
He said, given his findings and similar findings by other researchers in the past, any cases of SIDS where S. aureus is isolated from sterile sites should be considered for reclassification.
Professor George Haycock, scientific advisor to the Foundation for the Study of Infant Deaths, said: "The suggestion that infectious organisms such as S. aureus and E. coli play a part in a proportion of sudden infant deaths provides us with another important piece of the SIDS puzzle.
"It is important to recognise that both S. aureus and E coli are ubiquitous organisms carried by most, if not all, of the healthy adult population and that colonisation of infants does not imply lack of hygiene or normal care, but is bound to happen in a proportion of individuals.
"How deaths involving these organisms, by either of the mechanisms outlined above, can be prevented is not known at present since colonisation of some infants is inevitable."