Two people in the US, who have travelled recently to Germany, are being tested for the strain, said the US Centers for Disease Control and Prevention (CDC).
Spain says it will seek damages from Germany over initial claims that its produce was the source of the outbreak.
Spanish Prime Minister Jose Luis Rodriguez Zapatero said he would demand reparations for the economic losses suffered.
Germany had blamed Spanish cucumbers but has since accepted it was not the case.
Spanish fruit and vegetable exporters estimate they are losing 200m euros ($290m; £177m) a week in sales.
Sales of Spanish produce to supermarkets across Europe - not just of cucumbers, but of everything - have ground to a halt, says the BBC's Sarah Rainsford in Almeria, Spain's so-called fruitbasket.
Tens of thousands of kilos of fresh fruit and vegetables grown in Spain are being destroyed, she adds.