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.
“The best procedure is statistical analysis,” said Wieler, a member of a government commission on diseases that are spread to humans from animals.
In fact, the Robert Koch Institute, the government agency assigned to cope with the outbreak, said on Monday that it had begun the third such study.
Some scientists complain that health systems in the US and Europe are not using all available tools to better diagnose patients with toxic E. coli; earlier detection would allow for more effective treatment and limit the scope of outbreaks, they say. Routine tests for patients with bloody diarrhea look for other germs — shigella, salmonella and campylobacter — but not E. coli. Such tests are readily available, but more expensive.
“This suffered from a lack of primary diagnosis, and that’s crucial because no one is looking for it,” said Flemming Scheutz, the Copenhagen-based head of a WHO laboratory that specializes in E. coli. “The first alert didn’t go out until people were hospitalized.”
Likewise, Scheutz expressed concern that the decentralized German health system had made doctors initially unaware of the scope of the outbreak, familiar only with the cases in their region. A nationwide reporting system collects such information in the US
Overall, however, German officials had acted logically in confronting “one of the worst E. coli outbreaks ever,” said Frederic Vincent, a European Commission spokesman for health and consumer policy.
Vincent defended their decision to publicly blame Spanish cucumbers, even though it proved unfounded and has decimated Spain’s farm economy. He said 80 percent of the ill German patients had recalled eating the vegetable, that many of Europe’s cucumbers were grown in Spain and that initial tests had revealed the presence of E. coli on Spanish cucumbers — though it later proved to be a different strain.
E. coli strains range from benign to highly toxic. Accordingly, infections — which occur when the bacterium is ingested — range from mild disease to a potentially deadly. The toxin-producing strains can result in severe bloody diarrhea and, in some cases, a syndrome characterized by kidney failure and anemia that can be deadly.
There were about 3,500 confirmed cases involving those strains in the EU last year, Vincent said, and nearly 1,000 in Germany in 2008, according to the European Center for Disease Prevention and Control. However, many if not most cases probably go undetected. A few countries, like Ireland and Denmark, test aggressively for the disease, so their numbers appear high, Scheutz said.
The outbreak in Germany was caused by a relatively rare strain of E. coli, O104:H4, which possesses two potentially deadly qualities encoded into its genes: It produces the so-called shiga toxin and it also sticks to intestinal walls.
Alfredo Caprioli, who runs the EU reference laboratory for E. coli in Rome, said the strain had previously been identified as the culprit in a few cases, including two in Germany in 2001; in those no food source was ever implicated.
Because the strain is rare, scientists remain uncertain of just how much toxin it produces or even where it hides in nature, which make tracing and combating the outbreak more difficult. The high number of severe illnesses in the current outbreak could be because the strain is extraordinarily virulent, because the food that caused the outbreak was highly contaminated or because a huge number of people were exposed to it, Tauxe said.
Two weeks into the outbreak, German health officials have much to sort out.
“These can take a very long time — we may never find it,” Vincent said, adding that a 2006 E. coli outbreak that resulted from contaminated spinach originating in California took more than a month to work out. “But hopefully we can get very lucky.”
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