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Resistant bacteria increasing source of muscle infection

September 26, 2006

An antibiotic-resistant bacteria called methicillin-resistant Staphylococcus aureus (MRSA) is increasingly a cause of muscle infections in children, said Baylor College of Medicine (BCM) researchers in a report in the journal Clinical Infectious Diseases.

The report appears online at http://www.journals.uchicago.edu/CID/journal/contents/v43n8.html in the October 15, 2006, issue.

"We had noticed an increase in the number of muscle infections," said Dr. Pia Pannaraj, a post-doctoral fellow in the department of pediatrics' section of infectious diseases at BCM. She said that in recent years, she and her colleagues at Texas Children's Hospital had started to see a case of the MRSA muscle infection every month. In the cases she studied, the infection was acquired in the community, she said.

"I think it is important for parents to be aware that this bacterial infection can exist," she said. "They should seek care from their child's primary physician if there are symptoms of such an infection, such as a child limping or if there is redness or swelling in an extremity."

Houston, in particular, has a high rate of MRSA infections. More than 75 percent of community-acquired staphylococcal infections treated at Texas Children's Hospital are MRSA (resistant to the antibiotics commonly used to treat these infections in the past), she said. The rate of such infections is increasing nationwide.

In surveying patient records, Pannaraj and her colleagues found that in 60 percent of the 45 previously healthy children with the muscle infections called myositis and pyomyositis, the cause was a form of bacteria - either Staphylococcus aureus or Streptococcus pyogenes. The infections occurred between 2000 and 2005. Fifteen of the 26 S. aureus infections tested were methicillin-resistant Staphylococcus aureus (MRSA) forms of the bacteria that were circulating in the community. The other infections were forms of staphylococcal bacteria that were not resistant to methicillin, an antibiotic.

It is important the doctors treating patients for skin infections such as cellulitis to use antibiotics that will cure the resistant forms of the bacteria, said Pannaraj.

"Be aware that this is out there," she said. "When someone comes in, doctors should be aware that this could be a muscle abscess."

Antibiotics that successfully treat MRSA include oral clindamycin and trimethoprim-sulfamethoxazole, which are usually used out of the hospital, and vancomycin or clindamycin, which is given intravenously, usually to hospitalized patients.

The form of MRSA that is acquired in the community spreads more easily than that usually caught in the hospital, said Pannaraj.

"That's why I am seeing it in otherwise healthy children," she said.

She and her colleagues are trying to find out why this particular form of the bacteria spreads so easily. Her studies are focusing on specific genes. One, pvl, permits holes to be poked into the cells, damaging them irreparably.

"There seems to be an association between bacteria carrying the pvl gene and the severity of disease," she said. However, she said, they have not yet determined whether the problem is this specific gene or another that is close to it.

Others who participated in this research include: Drs. Kristina G. Hulten, Blanca E. Gonzalez, Edward O. Mason, Jr., and Sheldon L. Kaplan, all of the section of infectious diseases in the department of pediatrics at Baylor College of Medicine and Texas Children's Hospital.

Baylor College of Medicine