The hit-and-miss struggle of German health authorities to identify the contaminated food behind one of the deadliest E. coli outbreaks in recent years underscores the difficulties of following a pathogen through the complex food supply chain, as well as deficiencies in even the most modern health systems in diagnosing this deadly illness.
After mistakenly suggesting that Spanish cucumbers were the likely culprit several days ago, German authorities on Sunday focused on bean sprouts from a German farm, only to report on Monday that the first 23 of 40 samples from that farm had tested negative for E. coli. The results from the remaining samples had yet to come back. That does not entirely eliminate the farm as the outbreak’s origin, since even one positive test is sufficient to make the connection.
However, determining the origins of an outbreak that has killed 24 people and left 600 in intensive care presents a difficult mystery to unravel, with vital clues disappearing day by day as contaminated food is thrown away and farm and factory equipment is cleaned. Patients — whose illnesses first alerted health authorities to the outbreak — may have only cloudy memories of the meal that landed them in the hospital. Did the sandwich last month in Hamburg contain sprouts, tomatoes, lettuce, cucumbers — or all four?
After E. coli infection, diarrhea can take a week or more to emerge and it takes another week before the most serious complications, like kidney failure and anemia, occur. That means that as German investigators interview patients and visit farms to hunt for traces of the germ, the smoking gun may be long gone.
Finding the offending food “is sometimes going to be easy and sometimes going to be difficult and I think this is one of those,” said Robert Tauxe, deputy director of the division that handles foodborne diseases for the US Centers for Disease Control and Prevention.
“What did you eat four weeks ago?” Tauxe said. “You’re dealing with memory here — so it’s hard to pull apart.”
He said that even if hundreds of patients’ stories pointed investigators to a particular food — say, bean sprouts — it might be impossible to prove conclusively that they are to blame. To do so, scientists must visit the restaurant, farm or food processing plant and find the germ in water, or on food or other material.
“Even if all the samples are negative, maybe you just missed it,” Tauxe said. “You can go to a place reeking of chlorine, and find nothing.”
Indeed, the largest serious outbreak of E. coli, which sickened more than 8,000 people in Japan in 1996, has been widely attributed to eating contaminated radish sprouts, but scientists were never able to prove it in the laboratory.
Under pressure from the public and the news media, German health officials have struggled to identify the source of the E. coli, but have mostly succeeded in sowing confusion. First the Spanish cucumbers were blamed, and more recently the bean sprouts from Lower Saxony. Much of the information has come from local authorities acting independently, which adds to the appearance of official chaos.
The only reliable way to identify the source of the disease is by questioning victims about their food consumption and comparing them to a control group of healthy people with similar eating habits, said Lothar Wieler, a professor of veterinary medicine at the Free University of Berlin. Statistical analysis should then provide clues about the source.