Seven children have been hospitalized with serious infections after undergoing the same dental procedure at an Anaheim clinic, and public health officials said Tuesday they are contacting the parents of 500 other children who also had the treatment there.

The patients all received pulpotomies at Children’s Dental Group beginning May 3. The procedure, sometimes called a baby tooth root canal, removes infected pulp in order to prevent tooth loss.

The clinic stopped performing the procedure on Sept. 6, according to the Orange County Health Care Agency. In a written response to questions, Sam Gruenbaum, CEO of the chain of dental clinics located throughout the state, said the company is working to identify the source of infection and conduct follow-up exams on the patients who had the procedure.

“We follow industry standard sterilization and preventative practices and have looked closely at these, as well as reviewing our practices with the Orange County Health Agency,” Gruenbaum said. “We care deeply about our patients, and are doing everything we can to resolve this.”

The children developed oral cellulitis – a bacterial infection of the mouth that can spread to the gum and bone – and one tested positive for Mycobacterium abscessus, the agency said. Mycobacterium is a commonly occurring bacteria that generally poses no health risk, but on rare occasions can contaminate a water source.

Preliminary lab results for the other children are expected next week.

Dr. Eric Handler, Orange County’s health officer, said treatment requires intravenous antibiotics, often long-term and of multiple types, and possible surgery to remove the infection. He said the risk of infection to the 500 other patients the agency is contacting is considered low.

Handler said the infection source at the clinic has not been confirmed.

“We think it has to do with the water sources. As to why, we’re still investigating that,” Handler said.

Last year in Georgia, nine children were hospitalized with Mycobacterium abscessus infections after undergoing pulpotomies at a common clinic. An investigation found that the outbreak was caused by contaminated water that introduced the bacterium during irrigation and drilling.

The clinic did not monitor water quality or bleach waterlines at the end of each day as recommended, according to data published by the Centers for Disease Control and Prevention.

In that outbreak, Handler said, only about 1 percent of children who underwent the procedure became ill. He said symptoms may include persistent fever and swelling that doesn’t respond to treatment.

“Any time you have a surgical procedure, you have an opportunity for some type of infection if precautionary measures are not taken,” Handler said. “This procedure requires an opening of the tooth to preserve the pulp. Any kind of invasive-type procedure is at risk for that.”

Among the Orange County children with infections, symptoms began 15 to 85 days after the pulpotomy. Many of the hospitalizations occurred within the last week, the agency said. No other infections have been identified at other local dental practices or Children’s Dental Group clinics.

Gruenbaum said all children who had the procedure from May to September at the East Lincoln Avenue office are being asked to return for a follow-up visit that will include an exam by a dentist, X-rays and questions about fever, swelling and pain.

He said if no treatment is required, patients will be sent home with information and asked to return again to make sure they remain healthy.

In Southern California, Children’s Dental Group also has an office in Santa Ana and several in Los Angeles County.

The Health Care Agency has posted information for parents here.