The E.coli bacterium responsible for a deadly outbreak of disease in Germany that has left 18 people dead was revealed yesterday to be a new virulent strain, fuelling alarm across Europe.
Russia extended its ban on the import of vegetables from Germany and Spain to the entire European Union - a move condemned by the EU as disproportionate - while scientists said the new strain was similar to one isolated in the Central African Republic known to cause serious diarrhoea.
The World Health Organisation (WHO) said preliminary genetic sequencing suggested that the cause of the outbreak was a mutant form of E.coli that appeared to be particularly aggressive, resulting in widespread severe disease and deaths.
More than 1,500 people have been seriously affected, with at least 470 developing severe complication-causing kidney failure. Most of them are in Germany but at least 10 countries have reported people falling ill.
In the UK, seven people have been hospitalised including three Britons who recently visited Germany and a German person on holiday in England.
Hilde Kruse, a food safety expert at the WHO, said that the new strain had "various characteristics that make it more virulent and toxin-producing" than existing strains. "This is a unique strain that has never been isolated from patients before," she said.
However she stressed that milder cases were unlikely to seek medical help so it was impossible to know how big the outbreak was or what proportion were severely affected.
E.coli outbreaks have previously hit children and the elderly hardest and are usually linked with the consumption of meat and meat products, especially beef.
The European outbreak is disproportionately affecting adults, especially women, and has been linked with raw salad vegetables.
Experts said there might be something particular about the strain that makes it more dangerous for adults. The use of manure as a fertiliser could have led to contamination of vegetables.
The UK Health Protection Agency (HPA) said consumers should thoroughly wash or peel all salad and fruit before eating. But Dr Nicola Holden, of the James Hutton Institute, said washing may not be enough. She said the outbreak could be an indication that fruit and vegetables are actually ingesting the bacteria as they grow.
"The bacteria are able to get from animal sources onto crops through different routes, most likely in irrigation water or sometimes from slurry spraying, while some contamination can also occur during processing and packaging," she said.
The source of the outbreak remained a mystery yesterday. German officials have warned people not to eat lettuce, tomatoes and cucumbers, fanning uncertainty about the safety of the vegetables.
They had initially singled out Spanish cucumbers as the culprits but these were later cleared, prompting protests from Prime Minister, Jose Luis Rodriguez Zapatero, who said yesterday the government would demand "explanations and reparations" from Germany and the EU.
Questions and answers... the dangers, the symptoms, the medical advice
What is E.coli and how do we catch it?
Escherichia coli (E.coli) is a bacterium commonly found in the gut of humans and warm-blooded animals. Most strains are harmless but some, such as enterohemorrhagic E. coli (EHEC), can cause serious illness.
People catch E.coli mostly through foodstuffs, including raw or undercooked ground meat products and milk. Examples of foods involved in previous E.coli outbreaks include undercooked hamburgers, dried cured salami, unpasteurised fresh-pressed apple cider, yoghurt, cheese and milk.
An increasing number of outbreaks have been linked with eating fruit and vegetables (such as sprouts, lettuce, coleslaw, salad). In these cases, contamination occurs due to contact with animal faeces.
EHEC is destroyed by cooking foods thoroughly to a temperature of 70C or higher.
What about this latest strain?
Scientists are still trying to work out exactly which strain of E.coli is causing such devastating consequences in humans. Researchers in China have said preliminary genetic analysis of the outbreak suggests the bacterium is unique. They point to genes from two distinct groups of E. coli: enteroaggregative E. coli (EAEC) and EHEC.
What are the symptoms of E.coli?
Symptoms of EHEC include abdominal cramps and diarrhoea that may be bloody. People may also experience fever and vomiting. Many of the victims who have been identified so far have these symptoms.
The incubation period for EHEC can range from three to eight days, but is typically three to four days. Most patients recover within 10 days, but a small number will go on to develop haemolytic uraemic syndrome (HUS).
People with HUS suffer acute renal failure and, in some cases, damage to the central nervous system. It is estimated that up to 10% of patients with EHEC infection may develop HUS, with 3% to 5% dying as a result.
It is possible to pass EHEC to other people, which is why health experts urge good hygiene.
What health advice is being given?
All the people in the UK affected by the outbreak have travelled to Germany. The Health Protection Agency (HPA) says people travelling to Germany should avoid eating raw tomatoes, cucumbers and leafy salad including lettuce, especially in the north of the country. Anyone returning to the UK from Germany who feels unwell, including having bloody diarrhoea, should seek urgent medical help. The Food Standards Agency in the UK has issued general advice on the need to wash fruit and vegetables. Peeling or cooking fruit and vegetables may also remove germs.