Authorities are advising Germans not to eat raw homegrown sprouts, pointing to suspicions that the seeds may be one cause of the country's deadly E. coli outbreak.

Officials on Friday traced the outbreak to sprouts from a farm in northern Germany but are still puzzling over how the bacteria got there — whether through workers, seeds or by other means.

The federal risk assessment agency said authorities suspect homegrown sprouts may be behind one infection in a family in northern Germany — though it says tests so far haven't found the bacteria in the seeds.

The sprouts were first fingered as a likely cause by regional officials nearly a week earlier, but authorities backtracked when initial tests turned out negative.

All the while, a warning against cucumbers, tomatoes and lettuce, based purely on patient interviews, remained in place, causing major losses for farmers — especially in Spain. 

Hamburg officials for days fingered Spanish cucumbers as the probable source, but tests cleared them. 

The European Union's health commissioner at one point warned Germany against issuing more premature conclusions about the origin of contaminated food.

Cases involving the aggressive strain of E. coli began appearing at the start of May, and the outbreak swelled to crisis level over the next three weeks — with the German city of Hamburg at the epicenter.

It appears to be waning after sickening more than 3,000 people and killing 36, all but one of them in Germany.