MILAN, Italy – Sudden Infant Death Syndrome, in which apparently healthy babies die inexplicably in their cribs, may be linked to infection with a common bacterium, preliminary research suggests.

Researchers told a conference on infectious diseases Thursday that a shock-producing byproduct of E. coli was found in the blood of all SIDS babies tested, but in none of the infants used as a comparison. Experts not connected with the research said the toxic infection theory is plausible.

SIDS describes unexpected deaths that autopsies can’t explain. Despite decades of research, scientists remain mystified by crib death, the top killer of babies aged between 1 month and 1 year in the industrialized world.