U.S. health officials say it's safe to assume the tainted E. coli spinach outbreak is over given that a month has passed without any new incidents of illness.

"All evidence points to this outbreak having concluded," Dr. Kevin Reilly of the California Department of Health Services said Thursday. The last illness linked to the tainted spinach was reported on Sept. 25.

Authorities are also encouraging consumers to begin eating spinach again. Researchers with Western Growers, an organization representing farmers in California and Arizona, said the industry can expect losses of up to $74 million US.

Meanwhile, authorities are continuing their investigation and have found six new samples of E. coli bacteria at a California ranch located in San Benito and Monterey counties. Tests have shown samples taken from stream water, a wild pig and cattle match the O157:H7 strain found in the bagged spinach.

Authorities are reluctant to pinpoint one ranch as the definitive source, saying they are also inspecting three other farms in the region. About 750 samples have been tested from the four ranches.

"We are not saying this is the source at this point," Reilly said of the ranch.

Officials continue to examine other possible causes including runoff, flooding, irrigation, fertilizer and other wildlife.

Three people died and 204 people, including one Ottawa woman, were sickened by the contaminated spinach.

The Canadian Food Inspection Agency is continuing to warn consumers not to eat fresh spinach imported from the U.S.

E. coli stands for Escherichia coli, bacteria commonly found in the intestines of animals and humans.

With files from the Associated Press