BERLIN – Cucumbers were back on the radar of German health authorities Wednesday as the possible cause of an E. coli outbreak in Europe that has killed at least 26 people and sickened more than 2,700 others.

Two weeks ago, investigators blamed cucumbers from Spain for the deadly outbreak and then later ruled them out as the source. Then, the focus shifted to sprouts from northern Germany, but none that were tested turned out to be contaminated with the bacteria strain blamed for the outbreak.

Now, suspicions have fallen on a cucumber of an unknown country origin that sickened a family in eastern Germany. The cucumber — the first food found to be contaminated with the strain that has made thousands ill — was in the family’s compost, but there is no conclusive evidence that it’s the source.

“It’s unclear whether the cucumber infected the people, or the people the cucumber,” said Holger Paech, the spokesman for Saxony Anhalt state’s health ministry.

The father of the family had diarrhea, the mother was hospitalized for several days and their 22-year-old daughter is among about 700 people across Europe with a severe complication that can lead to kidney failure. She has been hospitalized for almost two weeks.

“The family was sick,” Paech said. “So, they could have contaminated the cucumber instead of the other way round.”

Laboratory tests on other samples taken from their house and from shops where they usually buy their vegetables all tested negative for the bacteria, he added.