European investigators fitting together the puzzle pieces of devastating E. coli outbreaks in Germany and France cautiously identified a likely source on Wednesday: contaminated fenugreek seeds from Egypt.

Officials also said that the seeds seemed to have entered Europe through a single German importer, which acted as a distributor to other companies.

A report by the European Food Safety Authority said that sprouts grown from fenugreek seeds imported from Egypt in 2009 and 2010 “are implicated in both outbreaks.” But it added that “there is still much uncertainty about whether this is truly the common cause of the infections” because tests on the seeds had not yet found any of the deadly E. coli, a rare strain known as O104:H4. Food safety experts say, however, that the bacteria can contaminate one seed in thousands and that it is very difficult to isolate in seed samples.

The devastating E. coli outbreak first surfaced in Germany in early May, eventually striking more than 4,000 people, nearly all of whom lived in Germany or had traveled there. The bacteria causes acute diarrhea and, in severe cases, kidney failure. At least 48 people died, according to the European Center for Disease Prevention and Control.