LONDON — Outside health experts and German lawmakers roundly criticized Germany on Tuesday for a bungled investigation into the world’s deadliest E. coli outbreak, saying the infections should have been spotted much sooner.

Many experts have been surprised, even shocked, at lapses in the German inquiry, and some say the culprit food may never be known.

Weeks after the outbreak began on May 2, German officials are still looking for its cause. Spanish cucumbers were initially blamed, then ruled out after tests showed they had a different strain of E. coli. On Sunday, investigators pointed the finger at German sprouts, only to backtrack a day later when initial tests were negative. The sprouts are still being tested.

“If we don’t know the likely culprit in a week’s time, we may never know the cause,” said Dr. Guenael Rodier, a director at the World Health Organization.

Rodier said the contaminated vegetables have probably disappeared from the market and it will be difficult to link patients to tainted produce weeks after they first became infected.

So far, the super-toxic strain of E. coli has killed 24 people, infected more than 2,400 and left hundreds hospitalized with a serious complication that can lead to kidney failure. New cases are reported every day – 94 more in Germany on Tuesday.

Other experts were more critical of the German investigation.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said officials should have done more detailed patient interviews as soon as the outbreak began to trace cases of illness to infected produce.

Tests on current produce won’t be helpful, he said. “It’s like looking at camera footage of a traffic intersection today to see what caused an accident three weeks ago.”

“If you gave us 200 cases and five days, we should be able to solve this outbreak,” added Osterholm, whose team has contained numerous food-borne outbreaks in the United States.

He also disputed the idea it might be impossible to find the source: “To say we may never solve this is just an excuse for an ongoing bad investigation.”

German lawmakers also slammed the government’s response to the outbreak, criticizing the confusing announcements and retractions.