May 27, 2011 (CIDRAP News) – Questions abounded today concerning the large and growing outbreak of Escherichia coli infections concentrated in northern Germany, including where it came from, why it is striking mostly women, and why the number of reported hemolytic uremic syndrome (HUS) cases, at 276, is so unusually high.
One thing seemed clear: the outbreak is shaping up to be one of the largest, if not the largest, E coli epidemics on record. The total number of illness cases was unclear today, but it appeared to be at least several hundred. The World Health Organization (WHO) cited 276 HUS cases and said three women have died.
"The current events represent one of the largest described outbreaks of HUS/STEC [Shiga toxin-producing E coli] worldwide and the largest in Germany, with a very atypical age and sex distribution of the cases," a team of experts wrote in a Eurosurveillance report published yesterday.
Tests in two German labs pointed to E coli O104, an unusual serotype that has caused only one previous known outbreak, in the United States in 1994, according to the Eurosurveillance report. German specialists also found that the strain is resistant to a number of antibiotics, including third-generation cephalosporins, the report said. (A ProMED-mail moderator noted in a post today that antibiotics should not be used empirically in E coli infections because they increase the risk of HUS.)
As reported previously, cucumbers from Spain are suspected as the possible source of the outbreak. The European Commission said in a statement today that German authorities identified organic cucumbers from two Spanish provinces as "one of the sources" and that a third batch of cucumbers from the Netherlands is also under investigation.
A case-control investigation in Hamburg, focusing on 25 case-patients and 96 matched healthy people, pointed to raw tomatoes, cucumbers, and leafy salads as possible sources of the pathogen, the Eurosurveillance report said. That prompted German authorities to warn consumers against eating those foods, especially in northern Germany.
The WHO statement today, in reporting 276 HUS cases with 3 deaths, commented, "The outbreak is unusual in that it has developed very rapidly, and an unusually high number of cases affect adults (86% are in people aged 18 years or older), particularly women (67%), instead of the normal high-risk groups, which are young children and the elderly. Nevertheless, cases have also been reported in school-aged children."
Yesterday's Eurosurveillance report put the number of HUS and suspected HUS cases at 214, including 119 from three northern German states. The report also cited 9 HUS cases in Sweden; 4 E coli cases, including 2 HUS cases, in Denmark; and 1 HUS case each in the Netherlands and the United Kingdom. Most of the patients had traveled to northern Germany.
HUS case count raises questions
HUS is a form of kidney failure that is potentially fatal. The report of 276 HUS cases raised eyebrows among experts today, because in past E coli outbreaks the number of HUS cases has typically been a small fraction of all cases.
One of the biggest previous E coli outbreaks was the O157:H7 epidemic linked to hamburgers from Jack in the Box restaurants in the United States in 1992 and 1993. A CDC report in 1994 put the total cases in the outbreak at 583 in four western states, with 41 HUS cases, for an HUS rate of about 7%.
Another large E coli outbreak was linked to fresh spinach from California fields in 2006. Officials counted 205 total cases, with 31 HUS cases, for an HUS rate of about 15%.
One infectious disease expert, Michael T. Osterholm, PhD, MPH, said the report of 276 HUS cases raises several questions, including whether the HUS diagnoses are accurate. Osterholm is director of the University of Minnesota Center for Infectious Disease Research and Policy, publisher of CIDRAP News.
"Are clinicians now diagnosing people with HUS when in fact they don't have it—they have bloody diarrhea but not HUS?" Osterholm asked. "Since HUS is a clinical case definition, we have to be very careful." He also noted that that few labs are equipped to test for non-O157 strains of E coli, such as O104.
If all the reported HUS cases are real, he said, "Then the question is, is that because there are so many E coli cases across Europe and we're just seeing the tip of the iceberg? Or is there something unique about this strain that causes HUS? We don't know that."
In previous E coli outbreaks the typical proportion of HUS cases has been about 1% to 3%, Osterholm said. He also noted that in foodborne disease outbreaks, the total number of cases may be 30 to 40 times the number that get reported.
Osterholm also said the outbreak may raise new questions about the safety of organic produce, if the link to organically grown cucumbers is confirmed.
Previous E coli O104 outbreak
The one previous reported outbreak of E coli O104 occurred in Helena, Mont., in 1994, according to a CDC report in Morbidity and Mortality Weekly Report (MMWR) in 1995. An investigation triggered by four cases of bloody diarrhea led to the detection of 11 confirmed and 7 suspected cases. The median age of the patients was 36, with a range of 8 to 63, and 12 patients were female.
A case-control study suggested that one particular brand of milk was linked to the outbreak, the report said. Internal records at the dairy that processed the milk showed some high coliform bacteria counts during the relevant time frame, but the outbreak strain was never found at the dairy or in the cows from the farms that produced the milk.
In other developments, the WHO said that Germany formally notified it of the outbreak, in line with International Health Regulations. The agency said it has offered technical assistance and "stands ready to facilitate collaboration between laboratories to assist countries without the capacity to detect the unusual E coli serogroup O104."
May 27 WHO statement
May 26 Eurosurveillance report
May 27 European Commission statement
1995 MMWR report on E coli outbreak in Montana
April 1993 MMWR report on Jack in the Box outbreak