# P-1147. Mupirocin Resistance Among Methicillin-Resistant Staphylococcus aureus Surveillance Isolates Associated with Invasive Infections, 2005-2022

## TL;DR

This study tracks mupirocin resistance in MRSA infections from 2005 to 2022 and finds no significant increase after 2014, despite its use in nasal decolonization.

## Contribution

The study provides updated surveillance data on mupirocin resistance in MRSA and evaluates its association with healthcare exposures post-2014 guidelines.

## Key findings

- High-level mupirocin resistance in MRSA isolates increased from <1% to 5.4% between 2005-2013 but stabilized afterward.
- No significant association was found between mupirocin resistance and recent healthcare exposures like surgery or ICU care.
- Continued monitoring is recommended to track resistance trends as decolonization practices evolve.

## Abstract

Nasal decolonization with mupirocin has been noted in professional society guidance since 2014 as an optional measure to prevent methicillin-resistant Staphylococcus aureus (MRSA) infection in certain high-risk settings or patients (i.e., intensive care unit [ICU] or undergoing high-risk surgery). Because of concerns about emergence of resistance, we evaluated trends in mupirocin resistance among MRSA isolates from invasive infections and associations between healthcare exposures and resistance.Figure 1.Percentage of methicillin-resistant Staphylococcus aureus isolates from invasive infections with high-level and low-level mupirocin resistance by year, CDC Emerging Infections Program surveillance, 2005-2022

Percentage of methicillin-resistant Staphylococcus aureus isolates from invasive infections with high-level and low-level mupirocin resistance by year, CDC Emerging Infections Program surveillance, 2005-2022

Isolates from the Emerging Infections Program active, population-based surveillance for invasive MRSA were submitted to CDC from a convenience sample of cases during 2005-2022. A case was MRSA isolated from a normally sterile body site in a surveillance area resident. Isolates were tested using reference broth microdilution and were considered mupirocin susceptible if the minimum inhibitory concentration (MIC) was ≤ 4µg/mL, low-level resistant (LLR) if MIC ≥ 8µg/mL and ≤ 256µg/mL, or high-level resistant (HLR) if MIC > 256µg/mL. Annual proportions of LLR and HLR isolates were calculated. Trends were assessed using the Cochran-Armitage test. For 2019-2022 isolates, healthcare exposures of cases with HLR vs. susceptible isolates were compared.

During 2005-2022, CDC tested 11,451 MRSA isolates for mupirocin resistance, representing 28.5% of total MRSA cases. Annual HLR isolates ranged from 0 – 6.1% (Figure). During 2005-2013, HLR isolates increased from < 1% to 5.4% (P< .001); during 2014-2022, HLR isolates ranged between 2.6%-6.1% with no significant trend (P=0.55). Cases with HLR (n=68) vs. susceptible (n=1,648) isolates during 2019-2022 did not have significantly different healthcare exposures, including: surgery ≤ 90 days (P=0.55) or ≤ 1 year prior (P=0.15), hospitalization ≤ 1 year prior (P=0.91), ICU care or presence of a central line ≥ 2 days prior (P=0.43 and P=0.53, respectively), or chronic hemodialysis (P=0.34).

Mupirocin resistance among invasive MRSA isolates did not increase significantly after the 2014 guidance and was not associated with selected healthcare exposures. Continued monitoring is needed to assess possible changes in mupirocin resistance as practices and additional strategies for nasal decolonization are evaluated.

William Schaffner, MD, Abbott Dignostics: Honoraria