ANAHEIM (CBSLA.com) — At least seven children have come down with what appears to be a bacterial infection after they had a procedure similar to a root canal at Children’s Dental Group in Anaheim, according to the Orange County Health Care Agency.

The agency has launched an investigation to find out exactly what made the patients sick. Health officials are contacting about 500 families with children who may have been exposed to the bacteria since May.

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Seven kids who were patients at Children’s Dental Group have been treated at Children’s Hospital of Orange County. Symptoms include abscesses in their mouths and necks, which have required surgery.

“The person sharing the same room, his son is here for the same reason and across the hall and next door,” said Christian Garcia, father of one of the sick kids who needed surgery. “You’d think they’d try to do something.”

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“It isn’t usually and issue of a person, it is an issue of an environmental source,” said Matthew Zahn of the Orange County Health Care Agency. “Either instruments or a water source, and that’s really what we’re trying to identify. We’ve gone out the facility multiple times; we’ve taken cultures of samples.”

Children’s Dental Group CEO Samuel Gruenbaum was interviewed by CBS2 News.

“I understand you want to talk about this, and I want to be helpful,” Gruenbaum said, “I’ll assure you, we are doing everything, whether it’s sterilization or anything else that relates to taking care of the patients, we are on it.”

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Last week, Children’s Dental stopped doing the procedure in question.