FRAMINGHAM, Mass. (AP) -- Criminal investigators from the Food and Drug Administration have visited a Massachusetts company whose steroid medication has been linked to a deadly meningitis outbreak.

FDA spokesman Steven Immergut said Tuesday the agents' work at the New England Compounding Center is part of the investigation into the outbreak, which has killed at least 15 people and sickened more than 200 others in 15 states. Nearly all the victims had received steroid injections for back pain.

Company attorney Paul Cirel says it's "difficult to understand the purpose" of the FDA search. He says the company has been clear it would voluntarily provide anything investigators requested. He says the company will continue to cooperate.

Federal and state investigators say they've found fungus in more than 50 vials from the company but haven't said whether they've pinpointed the contamination source.

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