While health authorities in Germany and neighboring countries deal with an outbreak of toxic E.coli, epidemiologists and doctors around the world are monitoring developments in Europe with especially keen interest.

Much remains unknown about the outbreak, but this much is clear: It is a very, very serious epidemic.

“The current events represent one of the largest described outbreaks of HUS/STEC (hemolytic uremic syndrome/shiga toxin E. coli) worldwide and the largest in Germany, with a very atypical age and sex distribution of the cases,” a Eurosurveillance report observed on Thursday. 

E. coli outbreaks occur frequently, almost daily.  But Germany’s outbreak is different, and troublesome in several ways.  Among them:

The sheer numbers:  Official counts are in the hundreds, but health officials understand that many more illnesses are probably going unreported.  It’s safe to assume the actual count is well into four digits.

The bug:  Most outbreaks of HUS, a life-threatening complication, in Germany and elsewhere are associated with E. coli O157:H7.  This outbreak, however, involves another strain, E. coli 0104, which is rarely encountered.

The HUS cases: Authorities are particularly alarmed by the high proportion of German victims hospitalized with HUS. Generally, only 10 percent of E. coli patients develop HUS, which is characterized by acute renal failure, hemolytic anemia and thrombocytopenia. In Germany, authorities report that more than 200 of the sick have developed HUS, and some reports put the figure at nearly 50 percent of the overall cases. This suggests that the German E. coli may be capable of of producing high levels of toxins, making it especially deadly.

As of Thursday, according to Eurosurveillance, the number of HUS patients in intensive care needing dialysis was putting a “severe strain” on hospital resources in some areas. And the outbreak did not seem to be abating. The high numbers of people showing up in emergency rooms suggested that “the source of infection is still active.”

The demographics:  E. coli infections are usually hard on two demographic groups — the very young and the very old. These are the people whose immune systems are least capable of fighting off the pathogens.  But Germany’s outbreak has been extraordinary in that it has affected mostly middle-aged women — a group that typically is not susceptible to the bug.   And nobody seems to know why.

“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,” the World Health Organization said Friday.

The investigation:  Germany’s outbreak was first detected nearly two weeks ago, but authorities are still grappling with enormous unknowns. One U.S. epidemiologist pointed out that the 0104 strain is difficult and time-consuming to identify, and that may well have delayed the process.

The source:  Organic cucumbers imported from two provinces of Spain (Almeria and Malaga) have been confirmed by German authorities as one source of the outbreak. A third batch of cucumbers from the Netherlands is under investigation. How the cucumbers became contaminated is unknown.