Antibiotic resistance, CA-MRSA makes susceptibility testing essential

Increases in the rate of community-associated methicillin-resistant Staphylococcus aureus combined with changes in patterns of antimicrobial resistance has led to a “a pandemic of staphylococcus,” according to a speaker at the AAP 2009 National Conference and Exhibition.

“There are two intersecting problems here. One is that we’re just seeing a lot more staph in the United States and the other is that we’re seeing changes in the patterns of antimicrobial resistance,” Robert W. Frenck, Jr., MD, a pediatric infectious disease specialist at Cincinnati Children’s Hospital Medical Center, said during the meeting this weekend.

Skin and soft tissue infections make up 85% to 90% of all pediatric CA-MRSA cases depending on the region, but CA-MRSA can also cause more invasive infections such as osteomyelitis, septic arthritis and necrotizing pneumonia if not managed properly.

Frenck, along with Carol J. Baker, MD,a practicing infectious disease specialist at Texas Children’s Hospital in Houston and Red Book associate editor, discussed how to best manage the wide spectrum of clinical manifestations associated with CA-MRSA infections.

“Mostly you are going to see mild to moderate infections. Presentations include insect/spider bite, cellulitis, folliculitis, pustular lesion, furuncle and abscesses,” Baker said. No matter the severity of infection, incision and drainage is the first step.

This procedure alone may be adequate for afebrile, previously healthy patients; however, Baker emphasized the need for thorough follow-up due to a lack of data regarding this technique in children. A good rule of thumb is gauging the size of the lesion, as evidence suggests this procedure is adequate for those lesions less than 5 cm.

Next, send the pus for susceptibility testing to determine the best antibiotic choice for patients in your community. “Because MRSA is so common there’s an ongoing debate as to whether we really need to culture these children,” Frenck said. “The answer is yes because antibiotic susceptibility is constantly changing.”

Clindamycin, trimethoprim-sulfamethoxazole (TMP-SMX) and doxycycline are antibiotics used to manage CA-MRSA.

Baker recommends performing a D test to determine inducible resistance before prescribing clindamycin. “In our particular area we know we have a high clindamycin resistant rate, so we’re using vancomycin in combination with nafcillin until we know antimicrobial susceptibility,” she said.

“In my community clindamycin resistance isn’t that high, but we’re having a hard time getting children to take the oral version because it tastes so bad,” Frenck said.

Although clinical experience suggests that TMP-SMX is effective, both Baker and Frenck emphasize caution when prescribing because data regarding its use in patients with staphylococcal infections is limited and retrospective in nature.

“Close follow-up is most important to me,” Baker said. “Even if you do all of the right things, a patient can still develop systemic symptoms. Tell parents to come back in if their child becomes febrile and keeps draining pus.”

Patients who appear toxic, who are immunocompromised or who have a limb-threatening infection should be hospitalized immediately and empirically treated with either vancomycin or clindamycin. Adding therapy with nafcillin, gentamicin or rifampin are other available options for critically ill patients, but clinical data are limited. – by Nicole Blazek

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