Five days after General Mills Inc. tripled the size of its flour recall — now at 30 million pounds — officials in China warned people there to stop using certain bags of Gold Medal flour because of possible E. coli contamination.

Unlike the expanded recall notice posted on the Food and Drug Administration’s website, the warning from the Centre for Food Safety (CFS) of China’s Food and Environmental Hygiene Department did not mention that the flour is linked to an ongoing outbreak that has sickened at least 42 people in 21 states. One in four has required hospitalization. Both FDA and China’s CFS say investigations are ongoing, which a General Mills spokesman confirmed Wednesday. He also said most of the recalled flour was sold in the U.S., but “a small amount” went to exporters who may have sold it to retailers outside the country. Investigations have yielded few results in terms of the root cause of the contamination. But, FDA’s outbreak investigators reported an increasing body of DNA evidence is revealing the outbreak strain of E. coli O121 is present in flour from a General Mills plant in Kansas City, MO. “Standard cleaning protocols have been followed and we have tested the facility for the presence of E. Coli O121 and all the tests have been negative,” General Mills spokesman Mike Siemienas said this week, declining to specifically address the operational status of the Kansas City plant. Minneapolis-based General Mills has been reporting all negative test results for the outbreak strain at the Kansas City plant since May 31 when it launched the initial 10 million pound recall of Gold Medal, Signature Kitchens and Wondra brand flours. The federal government’s evidence was compelling enough though, on May 31 and again on July 1, for General Mills to recall flour distributed to retailers, restaurants and bulk ingredient customers. As of this week, flour produced at the Kansas City plant from Nov. 4 through Dec. 14, 2015, is included in the recall. Product photos and label information that can be used to identify the recalled flour is available on the General Mills website. An elusive source So far, the government has been investigating the E. coli outbreak for about four months, beginning when warning signs started popping up at the Centers for Disease Control and Prevention. When patient interviews indicated raw dough as a common denominator, CDC looped in FDA. Both agencies credit high-tech laboratory tests for detecting the outbreak, which began Dec. 21, 2015, and for identifying the link to the General Mills flour. Containers of the recalled flour that were recovered from victims’ homes in Colorado, Oklahoma and Arizona tested positive for the outbreak strain. Investigators appear stumped, however, about how the E. coli got into the flour. FDA’s most recent report merely states the investigation is ongoing. The General Mills spokesman did not say whether the company had been able to rule out any possible sources, such as packaging materials or wheat. He also did not reveal whether the wheat suppliers for the Kansas City plant also supply other General Mills facilities. “We are continuing to collaborate with health officials on this investigation,” was his only response to questions about possible contamination sources. It could all come down to the neighborhood, so to speak. The General Mills plant at 2917 Guinotte Ave. in Kansas City sits on a sliver of industrial property surrounded by major rail and truck routes. The area is just north of downtown Kansas City. It’s only a few blocks east of Interstate 29. A poultry distribution company is directly across the street from the flour plant, and the area is a regular transportation route for trucks and trains hauling livestock. Dan Cohen of the agricultural research and development company Maccabee Seed in Davis, CA, is intrigued by the whole situation. “It’s still a little hard to imagine how the contamination took place,” said Cohen, who has been working in agriculture and food safety research and development for more than 30 years. “If it came in on grain, I would look for wheat sourced near feedlots because of dust contamination issues,” he said. Just as likely but much more difficult to track down, Cohen said, is the possibility the contamination source could be as simple as someone’s failure to properly clean a truck or trailer between different types of loads. (To sign up for a free subscription to Food Safety News, click here.)