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Maryland health officials are investigating possible cases of food poisoning at what may be the worst-ever venue — a gathering of government and industry leaders attending a national Food Safety Summit.

At least four people called the Baltimore City Health Department this week to report that they developed diarrhea, nausea and other symptoms about 12 hours after eating a meal April 9 during the conference at the Baltimore Convention Center.

That was midway through the annual meeting held April 8 to 10 that attracted more than 1,500 food safety professionals, including staff from federal agencies as well as businesses such as McDonald’s, Tyson, Chiquita and ConAgra Foods.

“None of us are very happy when we hear these things,” said Peggy Daidakis, executive director of the center.

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Word of the investigation spread Thursday when Bill Marler, a Seattle food safety lawyer, posted online a survey sent to him and other conference speakers and attendees asking them to report what they ate and how they felt after the meeting.

“We have not yet determined how people became ill, and we want your help to do so, even if you did not get sick,” wrote officials with the outbreak response unit for the Maryland Department of Health and Mental Hygiene.

That posting actually disrupted the data collection for the investigation, which is still in its early stages, said Sara Luell, spokeswoman for the agency.

City health officials inspected the convention center and its food service provider, Centerplate, said Michael Schwartzberg, a spokesman. The company was issued a violation notice for condensation dripping from one of the two ice machines in the kitchen, which was immediately fixed, he added. The firm had no violations during the most recent previous inspection.

Several officials with the federal Food and Drug Administration and the Centers for Disease Control and Prevention attended the gathering and may have been affected.

"A couple of our folks indicated that they had experienced symptoms associated with food poisoning after the summit," said Juli Putnam, an FDA spokeswoman.

No particular food has been identified in connection with the illnesses and no one who attended other conferences during the same time frame reported being sick, Luell said.

Officials at the center are cooperating fully with investigators to determine the cause of the illnesses, Daidakis said.

“We’re not trying to hide anything,” she added. “If there is something, we’ll take the corrective measures.”