Last Tuesday, a Swedish man with no apparent connections to Germany was infected with the bacteria, marking the first domestic case in Sweden.
"All previous Swedish cases had a connection to Germany, but not this," said Sofie Ivarsson, epidemiologist at the Swedish Institute for Communicable Disease Control (Smittskyddsinstitutet) to news agency TT at the time.
"This means that the source of the infection is in Sweden, which is a lot worse, because it might mean that there is some form of infected food product in circulation that we haven't yet identified."
After investigating possible sources to the man's infection, Eva Gustafsson, deputy epidemiologist in Skåne, tells TT that the efforts have been fruitless.
"We've followed all information to the end of the line, and right now we've run out of leads."
She doesn't believe there's any infected food to be worried about either.
"If that were the case, more people would have become sick," she said.
The man was the first, and thus far the only, person to have been infected with the EHEC version that has cost 47 lives in Europe so far.