A massive outbreak of E. coli is spreading through Europe, with 17 people dead in the last two weeks and 1,500 people sickened in Germany alone, where the outbreak began. Authorities are still trying to figure out where the outbreak originated and how it can be treated. What's Causing It:

What's the News:

• Scientists have identified the culprit as a strain of enterohemorrhagic E. coli (EHEC) which, unlike the generally harmless E. coli that live in our gut, releases toxins that damage capillaries in the intestine, leading to bloody diarrhea, gastrointestinal illness, and at times organ damage and even death.

• The various strains of EHEC are a common cause of food-borne disease, hitching a ride on foods from burgers to spinach. One common strain, O157, sickens 70,000 people in the US each year. The strain causing this outbreak is an extremely rare subtype called O104:H21, according to German health officials.

Why Is It So Dangerous:

• What makes this outbreak particularly bad is that large numbers of people---470 so far---have developed a sometimes fatal complication called haemolytic uremic syndrome.

• A German researcher found that the strain's DNA contains small sequences from other E. coli strains and from plague bacteria, which may help explain its ferocity---though there's no way, he emphasizes, that these bacteria could cause any form of plague.

Where's It Coming From:

• No one's sure. German officials initially pointed to cucumbers from Spain as the likely source of the outbreak, but conceded yesterday that they had misplaced the blame, after tests found the cucumbers weren't carrying the strain. (Spain, whose agriculture sector has been hit hard as many nations have banned or limited imports of Spanish produce, is considering legal action against Germany for impugning its veggies.)

• With the cucumbers cleared, health officials don't know what exactly the source of the outbreak is. Other types of produce are often implicated in food-borne disease outbreaks, so fruits and vegetables are still under scrutiny.

• E. coli is often spread when food, meat or water come into contact with cattle feces, but it's unclear whether this rare strain is transmitted the same way as more common ones. Wildlife feces or dirty factory equipment could also be transmitting the bacteria.

Who's Getting Sick:

• In Germany, more women have gotten sick than men; 61% of reported patients are female. Adult women account for a large majority of the patients who develop serious complications.

• The outbreak is centered in Germany, but has spread to six other European countries. A woman in Sweden who died from the infection is the only fatality thus far outside Germany; she had just returned from a trip there.

• Two US residents, both of whom recently went to Germany, seem to have contracted the infection and have been hospitalized.

What's the Treatment:

• When people develop HUS, they are typically given infusions of donor plasma to help get rid of the bacteria's toxins. (Antibiotics aren't used to treat EHEC because they can release a flood of the toxins, making things worse rather than better.)

• Shortly before the outbreak in Germany began, the New England Journal of Medicine accepted a paper on a new treatment for HUS caused by EHEC: using eculizumab, a drug used to treat a rare blood disorder. Three HUS patients, the researchers reported, were successfully treated with the drug.

• Some doctors in Germany are now using the drug to treat a few patients with severe HUS from the current outbreak. Very little is known about how well the drug works or what other effects it might have, and it's extremely expensive, costing €15,000 ($22,000) per patient. Doctors are using it only in cases where the regular treatments such as donor plasma haven't worked.

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