Methicillin-resistant Staphylococcus aureus (MRSA) rates are decreasing and S. aureus resistance to clindamycin is rising in the U.S. pediatric population, according to research from the U.S. Military Health System (MHS). MRSA rates have been declining in adult populations in the U.S., but clinical and demographic factors between adults and children may contribute to different antibiotic susceptibility trends.

Dr. Deena E. Sutter, from San Antonio Military Medical Center, Fort Sam Houston, Texas, and colleagues evaluated annual antimicrobial susceptibility trends of S. aureus from infections in pediatric patients receiving care in MHS treatment facilities from 2005 to 2014. Between 2008 and 2014, the annual number of S. aureus isolates declined by about 46 percent, according to an online report in Pediatrics.

Over the study period, susceptibility to erythromycin, gentamicin, and oxacillin increased, whereas there was a significant overall trend of decreased susceptibility to clindamycin, ciprofloxacin, and trimethoprim/sulfamethoxazole (TMP/SMX). Methicillin-sensitive S. aureus (MSSA) susceptibility to clindamycin decreased from 90.7 percent to 83.8 percent, whereas MRSA susceptibility to clindamycin remained stable. Despite the statistically significant decline in susceptibility to TMP/SMX, both MSSA and MRSA remained highly susceptible to this combination (around 98 percent susceptible).

“Our data demonstrate a steady decline in clindamycin susceptibility among MSSA,” the researchers concluded. “This trend may lead to some concern about the continued reliance on clindamycin for the empirical treatment of presumptive S. aureus infections although it is probably premature to abandon this effective antibiotic choice.”

“It is crucial that clinicians remain knowledgeable about local susceptibility rates as it would be prudent to consider alternate antimicrobial agents for empirical use when the local clindamycin susceptibility rate drops below 85 percent,” they noted. “In that situation, beta-lactams, TMP/SMX, or tetracyclines may be used for less severe infections with intravenous vancomycin employed in severe cases. If overall MRSA rates continue to decline and clindamycin-resistance among MSSA continues to increase, we may see a return to antistaphylococcal beta-lactam antimicrobial agents such as oxacillin or first generation cephalosporins as preferred empirical therapy for presumed S. aureus infections.”

Dr. Sheldon L. Kaplan, from Baylor College of Medicine, Texas Children’s Hospital, Houston, wrote an editorial related to this report. He told Reuters Health by email, “In the past two decades we have seen the emergence and then domination of community-associated (CA)-MRSA isolates causing both skin and soft tissue infections and invasive infections. This pattern seems to have peaked around 2007 to 2008 with a steady decline in CA-MRSA infections since then. I don’t think anyone knows why this is happening. Of course, this trend could change readily and CA-MRSA infections could be on the rise again at some point.”