U.S. military medical officers were awaiting test results from samples taken from the ill servicemembers -- and they could be confirmed late Friday or Monday, according to Phillip Tegtmeier, a spokesman for the US military's Europe Regional Medical Command.
"We're testing [for E. coli] as a precaution," he told military newspaper Stars and Stripes on Friday.
One of the U.S. servicemembers, an airman, remains in the hospital at the Spangahlem Air Base, in western Germany.
The other American reportedly affected was treated and released while based in Heidelberg, 48 miles south of Frankfurt.
The two suspected US military cases were among some 2,000 people hit by the E. coli outbreak across Europe, which so far claimed 18 lives, AFP reported.
The infection reportedly spread to a 12th country Friday, but all the deaths from the outbreak except one occurred in Germany. The other death, in Sweden, was a person who had just returned from Germany.
Authorities said they were no closer to identifying the origin of the outbreak Friday, but there were signs the number of infections was leveling out.
"The situation is that the number of new infections appears to be stabilizing somewhat," Reinhard Brunkhorst, president of the German Nephrology Society, told reporters in Hamburg, the epicenter of the scare.
But he added, "We are dealing here, in fact, with the biggest epidemic caused by bacteria in recent decades."
German chancellor Angela Merkel defended last week's false warning against organic Spanish cucumbers in a phone call Thursday with Spanish prime minister Jose Luis Rodriguez Zapatero, saying that authorities were "duty-bound to inform the public at all times."
The advisory, retracted this week, left tens of thousands of tons of Spanish produce unsold, costing Spanish growers an estimated €200 million ($290 million) a week.
"Both leaders agreed that the priority now must be to identify the source of the [E. coli] outbreak in order to be able to take further measures to protect the public," Merkel's spokesman, Steffen Seibert, said in a statement.
Russia, meanwhile, banned vegetable imports from the European Union in response to the scare, earning the ire of the European Commission, which called the move "disproportionate."
Scientific analysis has failed to show that contaminated vegetables are behind Europe's deadly E. coli outbreak, the EU's Reference Laboratory for E.coli in Rome said Friday.
"Alarmism over the consumption of vegetables is not justified ... since laboratory analyses do not support the hypothesis that contaminated vegetables were the source of the infection," the laboratory said in a statement.