Health officials have confirmed that four Canadians have been infected with the same strain of salmonella identified in a U.S. outbreak that has sickened at least 943 people.

Public health officials said Monday evening three of the people became ill after returning from a trip the U.S.

"Cross-border cases are expected given the size of the outbreak in the U.S., and travel by Canadians to the U.S.," the Canadian Food Inspection Agency and the Public Health Agency of Canada said in a release.

Canadian health officials confirmed the first case, which involved an Ontarian who had travelled to the U.S. on July 3.

Meanwhile, U.S. investigators have begun testing shipments of jalapenos imported from Mexico, the Washington Post reported Tuesday. The probe initially focused on tomatoes as the possible cause of the outbreak, though in recent days investigators said they were also testing cilantro and peppers.

FDA spokeswoman Stephanie Kwisnek told the newspaper "there is no specific 'prime suspect.'"

Tomato farmers who have been forced to leave their crops rotting in fields and packing houses estimate losses total about $100 million US.

Salmonella bacteria normally live in the intestinal tracts of animals and birds, but can be transmitted to humans who eat food contaminated with animal feces. Salmonella causes intestinal problems in humans, resulting in diarrhea, fever and cramps.

With files from the Associated Press