In The News: MRSA Resistance Increases

A study from 2012-2017, as reported by Healio, showed a percentage increase in U.S.-MRSA resistant to trimethoprim-sulfamethoxazole. Researchers used the Cerner Health Facts EMR and the Premier Healthcare Database to identify Staphylococcus aureus infections among inpatients discharged from acute-care hospitals.

The study authors identified cases of MRSA or methicillin-susceptible S. aureus (MSSA) to calculate the pooled mean percentages of MRSA and MSSA isolates that were not susceptible to TMP-SMX by year using weighted estimates. Between 2012 and 2017, they identified 232,460 MRSA-incident cultures and 227,900 MSSA-incident cultures.

Based on weighted estimates, 98.3% of all MRSA cultures underwent antimicrobial resistance testing (AST) for TMP-SMX, giving an estimate of 2,155,794 cases, among which 5.3% were not susceptible to TMP-SMX. Additionally, within the same period, a projected 98.5 of MSSA cultures received AST for TMP-SMX, and 1.4% of cases were not susceptible to TMP-SMX.

The estimated proportion of cases that were not susceptible to TMP-SMX increased 124.5% during the study period among MRSA cases (adjusted 5-year change; 95% CI, 87.7%-168.6%) and 51.3% among MSSA cases (adjusted 5-year change; 95% CI, 19.2%-92.1%).

PIDS member Sheldon Kaplan commented for the story, “Incision and drainage is the most important aspect in management of skin abscesses and trimethoprim-sulfamethoxazole (TMP-SMX) and clindamycin are the primary oral antibiotics for empiric adjunctive treatment of skin and soft tissue infections in children for which Staphylococcus aureus is by far the most common pathogen. A high proportion of S. aureus isolates causing community-associated infections in the United States are still methicillin-resistant and empiric antibiotic therapy following I&D of abscesses should target both methicillin-susceptible and methicillin-resistant S. aureus. 

“Thus, it is very concerning but not surprising that resistance to TMP-SMX is increasing along with similar reports for clindamycin resistance among S. aureus isolates in the US. Although increasing TMP-SMX resistance has definite implications for selection of empiric treatment of SSTIs, this increase may have a more important impact on the antibiotics available for completing treatment of some invasive infections (such as osteomyelitis or septic arthritis) caused by clindamycin-resistant MRSA isolates. Increasing resistance also complicates the selection of an antibiotic for treating these invasive infections for which S. aureus is the most likely etiology but no organism is isolated. 

“It is likely that clindamycin and TMP-SMX resistance among S. aureus isolates will continue to increase which highlights the critical importance of antibiotic stewardship measures to combat antibiotic resistance as well as the need for development of new antibiotics and hopefully one day, a vaccine to prevent S. aureus infections in the first place.”