S. aureus treatment patterns may be shifting

More physicians may prescribe clindamycin for Staphylococcus aureus infections as community-associated methicillin-resistant Staphylococcus aureus infections become more common, study findings suggested.

Researchers from Missouri investigated the use of commonly prescribed antimicrobial agents for S. aureus infections among inpatients at 25 U.S. children’s hospitals. They used data from the Pediatric Health Information Systems collected from 1999 to 2008 for their analysis.

The study cohort involved patients aged younger than 18 years who had diagnoses of S. aureus septicemia, MRSA or pneumonia caused by S. aureus. The researchers also classified the infections as MRSA or methicillin-susceptible S. aureus.

Antimicrobial treatments selected for the study included vancomycin, clindamycin, trimethoprim-sulfamethoxazole (TMP-SMZ), linezolid and beta-lactam antibiotics. The researchers examined percentage of use and days of therapy as measures for antibiotic treatment.

They found that 64,813 patients who had discharge diagnoses of S. aureus infection, with the incidence of MRSA increasing from two to 20.7 cases per 1,000 admissions during the study period (P<.001).

The overall percentage of antibiotic use indicated for MRSA treatment also increased from 52% to 79%. Clindamycin emerged as the more popular choice for all S. aureus infections, the researchers noted, with usage rising from 21% to 63% by 2008 (P<.001). Beta-lactam antibiotics used to treat methicillin-susceptible S. aureus infections only, however, saw a significant decline from 66% to less than 30% (P<.001).

Days of therapy for clindamycin use also rose from 53 to 192 per 1,000 patients (P<.001). Small increases occurred for TMP-SMZA and linezolid, according to the researchers, but days of therapy decreased from 33 to 18 for beta-lactam antibiotic treatments (P<.001).

For MRSA infections only, the researchers reported similar results, except vancomycin use decreased from 53% to 36% (P<.001). Days of therapy, however, grew from 204 to 248.

The researchers noted that the rise in use of MRSA-active agents, especially clindamycin for S. aureus infections, reflect the emergence of CA-MRSA and the problem it presents.

“It is essential that clinicians be vigilant in monitoring antibiotic susceptibilities as well as patient outcomes to ensure appropriate empiric and culture-directed therapy for S. aureus infections,” the researchers wrote. – by Melissa Foster

Herigon JC. Pediatrics. 2010;125:e1294-e1300.

These finding confirm what would be expected for the antibiotics administered to hospitalized children with S. aureus infections as a result of the dramatic increase in community-acquired MRSA isolates associated with skin and soft tissue, as well as invasive infections caused by S. aureus in most areas of the United States. The study apparently does not distinguish between community-acquired, community-onset health care associated (CO-HCA) and nosocomialS. aureus infection, which likely accounts for the greater number of children with pneumonia compared with those with osteomyelitis.

In our studies conducted in one large children’s hospital, osteomyelitis is by far the most common invasive S. aureus infection in children. It also was somewhat surprising to note that clindamycin and linezolid were administered frequently to children with endovascular infections. Neither is recommended by experts in this area because they are bacteriostatic in action, and an antibiotic that is cidal is optimal, which is pointed out by the authors. Perhaps these antibiotics were administered to these patients prior to documenting an endovascular infection. Outcome information would be particularly valuable in this group of children.

Finally, the authors’ conclusion that we must remain vigilant in monitoring antibiotic susceptibilities to ensure that empiric use of these agents, especially clindamycin, remains appropriate. In order to do this most appropriately, one must distinguish among true community-acquired S. aureus infections in otherwise healthy children vs. CO-HCA infections that occur in children with underlying conditions, or in children hospitalized in the past six to 12 months vs. those infections that are nosocomial. Clindamycin resistance increases among S. aureus strains as one compares community-acquired with CO-HCA to nosocomial isolates. Unfortunately, most hospital antibiograms cannot distinguish among these three groups.

– Sheldon L. Kaplan, MD
Infectious Diseases in Children Editorial Board

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