Health officials now say four people in the U.S. may be linked to the food poisoning outbreak in Europe.
All four were in northern Germany in May and officials are confident that they were infected with E. coli in that country. Three of them -- two women and a man -- are hospitalized with a kidney complication that has become a hallmark of the outbreak.
Officials said Friday they are also checking two possible E. coli cases in U.S. military service members in Germany.
The source of the outbreak hasn't been pinpointed but salad vegetables are suspected.
An official from the Food and Drug Administration says produce in the U.S. remains safe. The government has stepped up testing of imported food from Germany and Spain, but very little is imported from those countries.