July 23, 2018
2 min read

S. aureus infections increasingly resistant to clindamycin, TMP-SMX

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Methicillin resistance among Staphylococcus aureus isolates has decreased among children since 2005; however, researchers reported increases in resistance to clindamycin and trimethoprim-sulfamethoxazole, especially for methicillin-sensitive infections.

“When community-associated MRSA was on the rise from the 1990s through the early 2000s, clinicians sought alternatives to antistaphylococcal beta-lactams, and empirical treatment of presumptive S. aureus disease with clindamycin and trimethoprim-sulfamethoxazole, or TMP-SMX, became widespread,” Dina D. Khamash, MD, a postdoctoral research fellow in the division of pediatrics at the Johns Hopkins University School of Medicine, and colleagues wrote. “Recent data suggest that the prevalence of MRSA is decreasing, which prompts questions about what the appropriate empiric management should be.”s

To better understand trends in methicillin, clindamycin and TMP-SMX resistance in children with S. aureus, the researchers conducted a retrospective observational study in which they assessed bacterial cultures collected at The Johns Hopkins Hospital. These cultures were gathered from children aged younger than 18 years, between Jan. 1, 2005, and March 31, 2017.

For this study, Khamash and colleagues defined community-onset infection if the culture was collected no more than 3 days after admission and when the child had no hospital admissions in the past year. Additionally, the researchers included nosocomial infections if cultures were collected more than 3 days after admission.

S. aureus was detected in 2,431 initial cultures during the study period. Most isolates were methicillin susceptible (MSSA; 62%), and 38% were methicillin resistant.

Between 2005 and 2017, MRSA isolates dropped from 41% to 27%, with 43% of S. aureus isolates defined as community onset and 22% were health care related. Khammash and colleagues said resistance significantly lessen among those with community-associated infection (48% to 15%). Although methicillin resistance remained the same in children with hospital-associated, community-onset infection, a decrease was observed in nosocomial infections (32% to 13%).

Methicillin resistance decreased significantly in blood, respiratory, skin and soft tissue and other areas, according to the researchers.

Despite a decrease in methicillin resistance, an increase was observed in resistance to clindamycin (21% to 38% in MRSA) in this population, and a more significant increase was observed in clindamycin resistance in MSSA (5% to 40%). TMP-SMX resistance also increased in MRSA isolates (2% to 13%), but resistance in MSSA continued to be stable throughout the study (5% to 7%).

Children with community-onset infection demonstrated the highest rate of clindamycin resistance (7% in 2005 to 39% in 2017). These children also had the greatest increase in TMP-SMX resistance (3% to 13%).

Those who had hospital-associated, community-onset infections also demonstrated an increase in resistance, with Khamash and colleagues observing clindamycin resistance rising from 11% to 42%, and TMP-SMX resistance increasing from 3% to 8%. Resistance in nosocomial S. aureus infections increased for both clindamycin (24% to 43%) and TMP-SMX.

The researchers noted that previously conducted studies observed similar results with more significant increases in clindamycin resistance in MSSA.

“The epidemiology of S. aureus infection in children continues to evolve, which makes it important to align therapy with the most recent local antibiotic-susceptibility results,” Khamash and colleagues wrote. “With the rate of clindamycin resistance now higher than 40%, TMP-SMX resistance on the rise, and methicillin resistance declining, clinicians might need to reconsider empiric management of presumed S. aureus disease in children, especially those with community-onset infection.” – by Katherine Bortz

Disclosures: The authors report no relevant financial disclosures.