Jun 2, 2011 (CIDRAP News) – The official toll of enterohemorrhagic Escherichia coli (EHEC) cases in Europe climbed above 1,600 today, with at least 16 deaths, as the pathogen's source remained elusive and one team of scientists called the strain new and "super-toxic."
The World Health Organization (WHO) said today that the outbreak grew to 1,614 cases in Europe, including 1,115 cases classified as EHEC only and another 499 that involved hemolytic uremic syndrome (HUS), or potentially fatal kidney failure. The proportion of HUS cases and the percentage of HUS cases in adults (88%) have both been far higher than is usually seen in E coli outbreaks.
In Germany, 9 patients have died of HUS and another 6 have died of EHEC, and one person in Sweden has died, the WHO said. But an Associated Press (AP) report today put the total death toll at 18. Most cases have occurred in Germany, but nine other European countries have also had illnesses.
Three people in the United States are now hospitalized with HUS cases suspected to be related to the European outbreak, Lola Russell of the US Centers for Disease Control and Prevention told CIDRAP News today. The count is up one since yesterday.
Today's case numbers seemed to signal that the outbreak is slowing down little, if at all. A report published today in Eurosurveillance, covering events to May 31, showed that the daily number of HUS cases reported in Germany peaked at 39 on May 16 and has been generally dropping since then. But today's WHO statement noted that the number of German HUS cases yesterday was 470, an increase of 97 from the day before.
Also, because of the delay in reporting of cases, the Eurosurveillance report said, "The current notification data cannot be interpreted as a decrease in case numbers." The report was authored by specialists from Germany's Robert Koch Institute and the European Centre for Disease Prevention and Control in Stockholm.
Despite multiple investigations, there was no official word today of new clues about the source of the pathogen, the rare E coli strain O104:H4. Case-control studies have cast suspicion on cucumbers, tomatoes, and lettuce sold in northern Germany. But the outbreak strain has not been found on any of those items, despite an early finding of a pathogenic E coli strain on some Spanish cucumbers tested in Hamburg.
Meanwhile, a Chinese genomics laboratory, BGI (formerly the Beijing Genomics Institute), announced today that it has sequenced the outbreak strain and completed "a preliminary analysis that shows the current infection is an entirely new super-toxic E coli strain." The analysis was done by BGI-Shenzen in collaboration with the University Medical Centre Hamburg-Eppendorf, the BGI statement said.
The analysis confirmed that the pathogen is an E coli O104 but said it is a new serotype, "not previously involved in any E coli outbreaks," according to BGI. The strain is 93% similar to a strain found in the Central African Republic, but it has acquired sequences that seem similar to those involved in causing "hemorrhagic colitis" and HUS, the statement said.
The statement also said the E coli strain carries genes that confer resistance to several classes of antibiotics. Earlier reports from Europe had said the strain was resistant to multiple drugs.
A WHO official agreed that the outbreak strain is new, according to the AP report. "This is a unique strain that has never been isolated from patients before," said Hilda Kruse, a WHO food safety expert.
Earlier this week, the CDC called the outbreak strain very rare but not brand new. In today's AP story, Dr. Robert Tauxe, a CDC foodborne disease expert, said the strain was seen in a case in Korea in the 1990s. He said the genetic fingerprints of the current strain and the Korea one may vary slightly, but not enough to call the European strain new, according to the AP.
Craig Hedberg, PhD, a foodborne disease expert at the University of Minnesota School of Public Health in Minneapolis, cautioned that there is still too little information, genomic or otherwise, to explain why the outbreak strain is causing so many severe illnesses.
"I think it is too early to fully characterize this agent and what makes it as virulent as it appears to be," Hedberg commented by e-mail. "The rapid genomic analysis presents some interesting information, but detecting a gene is not the same as demonstrating what it means from the standpoint of disease transmission.
"The large number of cases diagnosed with HUS implies either a highly pathogenic organism, or a very large population exposed to the vehicle. It is too soon to really make those distinctions. A relatively small case-control study seemed to implicate fresh produce items, and this is certainly consistent with the demographics of the outbreak, but the size and distribution of the outbreak is also somewhat difficult to explain with a contaminated, imported produce item.
"Something very unusual has happened (is happening?), and we cannot be certain what it is," he added.
Referring to Tauxe's comments, Hedberg agreed that an HUS case involving a similar strain occurred in a 29-year-old Korean woman. "How this appeared suddenly and overwhelmingly in northern Germany is very disturbing," he said.
He also commented that the Robert Koch Institute has already learned much about the strain and shown that it has an unusual combination of features, but said the full extent of its virulence and its pathogenic mechanisms still need to be determined.
"The fact that it is a multi-drug resistant organism that is ESBL [extended-spectrum beta-lactamase]-positive may also have implications about the origin of the pathogen (ie, human source more likely than food animal source)," Hedberg said. "Much more will be learned about this as things develop."
Today's Eurosurveillance report gave a long list of continuing investigations into the outbreak, including case-control studies and an inquiry into human-to-human transmission in a "special outbreak in a canteen."
The report also said that among 13 deaths reported in Germany, 8 of the victims were between 75 and 91 years old, while the other 5 were between 22 and 40.
Jun 2 WHO statement
Jun 2 Eurosurveillance report
European Commission statement asking Russia to withdraw ban on produce from EU