By MIKE STOBBE
AP Medical Writer

NEW YORK (AP) - Health officials are reporting an outbreak of bacterial infections in patients who got injections of stems cells derived from umbilical cord blood.

At least 12 patients in three states - Florida, Texas and Arizona - became infected after getting injections for problems like joint and back pain.

All were hospitalized, three of them for a month or longer. None died.

Investigators don't think the contamination occurred at the clinics where the shots were given, because they found bacteria in unopened vials.

The government last month sent a warning letter to Genetech Inc., the company that processed the stem cells.

Stem cells are very young cells than can develop into specialized cells. Some doctors use them to try to repair damaged or diseases tissue.

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