British health workers are being told to look out for signs of serious illness linked to E.coli in people returning from Germany.
There have been two cases so far of German citizens in England with symptoms that indicate they may have caught the bug.
Germany is currently experiencing a large outbreak of haemolytic uraemic syndrome (HUS) - a serious complication of verocytotoxin-producing E. coli (VTEC) infection.
The strain of VTEC suspected in the outbreak is O104 - a strain rarely seen in Britain.
Victims require hospital treatment because HUS can affect the blood, kidneys and, in severe cases, the central nervous system.
Since mid-May, around 214 cases of HUS have been reported in Germany, particularly in the north, with two deaths.
Today, the UK Health Protection Agency (HPA) said the outbreak is mainly affecting adults - almost 70% of whom are women.
It warned travellers to Germany to avoid eating raw tomatoes, cucumbers and lettuce there, which are thought to be a possible source of infection.
Anyone returning to the UK with bloody diarrhoea should also seek urgent medical attention.
Dr Dilys Morgan, head of the gastrointestinal, emerging and zoonotic infections department at the HPA, said: "The HPA is actively monitoring the situation very carefully and liaising with the authorities in Germany, the European Centre for Disease Control (ECDC) and the World Health Organisation (WHO) as to the cause of the outbreak.
"We are keeping a close watch for potential cases reported in England and are working with colleagues in the devolved administrations to recommend they do the same.
"In addition we are in the process of alerting health professionals to the situation and advising them to urgently investigate potential cases with a travel history to Germany."
Other European countries have seen cases of HUS and bloody diarrhoea in people returning from Germany.
The Food Standards Agency is monitoring the situation for foods imported into the UK.