E coli cases slow as more details on pathogen emerge

Jun 14, 2011 (CIDRAP News) – German authorities investigating the nation's biggest Escherichia coli outbreak said today that the number of new cases has dropped significantly, as European scientists released the latest results from a genetic analysis of the unusual strain, which they say might have a human reservoir.

Germany's Robert Koch Institute (RKI) said in an update today that the numbers of new enterohemorrhagic E coli (EHEC) infections and hemolytic uremic syndrome (HUS) cases have markedly slowed. It said the latest illness onset for EHEC diarrhea was on Jun 9 and for HUS with diarrhea was on Jun 8. The outbreak is believed to have been caused by contaminated sprouts.

According to the European Centre for Disease Prevention and Control (ECDC), the latest totals include 2,514 EHEC cases and 818 HUS cases. Thirty-six deaths have been reported. Since yesterday the number of EHEC infections has risen by 6 and HUS cases by 1.

The number of deaths by the ECDC's count held at 36 earlier today, but German officials reported the death of a 2-year-old boy, the first child to die in the EHEC outbreak, Agence France-Presse (AFP) reported today. The burden of disease in adults, especially women, has been an unusual feature of the outbreak. EHEC outbreaks typically hit younger age-groups the hardest.

The boy died in a Hanover hospital, where he had been in intensive care for several days, according to the AFP report. His family had also been sick, but all were recovering.

Meanwhile, German authorities recently expanded their warning about eating sprouts to include home-grown products. Lower Saxony state reported that home-grown sprouts may be linked to a family's EHEC infections, which prompted officials to recommend that people also avoid homegrown raw sprouts, according to the latest update from Germany's Federal Institute for Risk Assessment (BfR). However, so far lab studies have not detected E coli O104:H4 in the seeds.

Dr Andreas Hensel, who heads the BfR, said in the statement that growing sprouts at home is common and that many stores sell cultivation receptacles. "If the seeds are already contaminated with germs, even observance of kitchen hygiene rules does not protect from an EHEC infection," he said.

On the scientific side, a report and accompanying editorial published today by Eurosurveillance provided additional details about the outbreak strain, E coli O104:H4, reinforcing previous reports that it has characteristics of both enteroaggregative E coli (EAEC) and Shiga toxin–producing E coli (STEC). The articles describe the strain as an EAEC that acquired the ability to produce Shiga toxin (verotoxin).

Because EAEC strains are common worldwide, the hybrid organism probably has a human rather than an animal reservoir, and it may be able to persist in humans for a long time, the authors say.

EAEC is a common cause of diarrhea in travelers and in children in developing countries and is one of the most important enteric pathogens in AIDS patients, say the two reports. "In contrast to STEC strains that have an animal reservoir, mostly ruminants, [EAEC] have a human reservoir," says the editorial, written by ECDC officials.

The research report, written by authors from Denmark, Italy, and the United States, says the rare serotype O104:H4 was seen previously in two HUS patients in Germany in 2001, one case in France in 2004, one HUS patient in Korea in 2005, two HUS cases in the Republic of Georgia in 2009, and one uncomplicated case of diarrhea in Finland in 2010.

The current outbreak strain bears a particular similarity to the Georgia strain, but the significance of the finding is unclear because there is no known epidemiologic link between the two outbreaks, the editorial states.

The authors of the research report express the view that the addition of the Shiga toxin factor to an EAEC strain already capable of causing persistent diarrhea has resulted in a "hypervirulent strain." Besides having the ability to produce Shiga toxin, the hybrid strain has a virulence factor (the receptor for iron-chelating aerobactin) associated with extra-intestinal E coli strains, such as those that cause urinary tract infections, they note.

"It should also be noted that [EAEC] are common in all populations of the world, industrialized and developing, but that no animal reservoir has been described," they add. "This observation suggests the startling possibility that this new O104 strain may have the capacity to persist among human populations, perhaps indefinitely."

See also:

Jun 14 Eurosurveillance report

Jun 14 Eurosurveillance editorial

Jun 14 ECDC update

Jun 12 BfR statement

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