SAN DIEGO The overall rates of resistance of pediatric Staphylococcus aureus isolates to clindamycin remained stable at around 11% in Southern California between 2004 and the first half of 2007, results from a large study of patients from that area demonstrated.
At the same time, overall resistance to both a ?-lactam and clindamycin remained stable at 2.8%, Dr. Mark B. Salzman reported at the annual meeting of the Infectious Diseases Society of America.
"We need to continue to monitor resistance rates of clindamycin and other antimicrobials," said Dr. Salzman, a pediatrician at Kaiser Permanente West Los Angeles Medical Center.
He and his associate, Susan M. Novak-Weekley, Ph.D., identified all S. aureus isolates from Kaiser Permanente Southern California patients under the age of 18 years between January 2004 and June 2007.
Kaiser Permanente Southern California is a large HMO system with 11 hospitals, 110 medical offices, and 839,000 patients under the age of 18. The researchers categorized the S. aureus isolates by year and by methicillin-resistant S. aureus (MRSA) status, methicillin-susceptible S. aureus (MSSA) status, and clindamycin susceptibility.
"Only one isolate per patient per year was counted, unless it was different in susceptibility to either clindamycin or oxacillin or if it was from a different source cultured more than 6 months later," Dr. Salzman said.
In 2004, there were 2,095 S. aureus isolates in patients under the age of 18 years, compared with 3,406 in 2005, 4,801 in 2006, and 2,329 in the first 6 months of 2007. MRSA accounted for 33% of isolates in 2004, 43% of isolates in 2005, 45% of isolates in 2006, and 46% of isolates in the first 6 months of 2007. "Since 2005 the pediatric MRSA rates seemed to have reached a plateau," he said.
The number of clindamycin suspension prescriptions nearly tripled over the time period, from 1,276 in 2004 to a projected 3,300 in 2007 based on data extrapolated from the first 6 months of 2007.
The number of prescriptions for clindamycin capsules rose from 41,427 to 70,000 in 2007 based on data extrapolated from the first 6 months of 2007.
Clindamycin resistance rates to MRSA isolates were 8% in 2004, 7% in 2005, 6% in 2006, and 7% in the first 6 months of 2007, while the rates of resistance to MSSA isolates were 13%, 17%, 15%, and 15%, respectively. The rates of clindamycin resistance to S. aureus, including both MRSA and MSSA, were 11.2% in 2004, 12.3% in 2005, 10.9% in 2006, and 11.2% in 2007. The percentage of isolates that were resistant to both ?-lactams and clindamycin were 2.7% in 2004, 2.9% in 2005, 2.7% in 2006, and 3.1% in the first 6 months of 2007, for an overall rate of 2.8%.
"All presumed S. aureus infections should be cultured if possible," said Dr. Salzman. "Clindamycin can still be used as empiric therapy for most nonserious S. aureus infections, but I think that combining a ?-lactam with clindamycin should be considered for empiric therapy of more serious S. aureus infections."
He advised that vancomycin be reserved "for life-threatening infections or very serious infections or empiric therapy when other therapies fail in the absence of culture and susceptibility confirmation."
Dr. Salzman disclosed that he is on the speakers' bureau for Sanofi Pasteur.