Staphylococcus aureus mupirocin susceptibility testing in a neonatal intensive care unit reveals horizontal transmission of a highly resistant strain
Andrea L. Ankrum, David B. Haslam, Joel E. Mortensen, Felicia Scaggs-HuangAbstract
Objectives:
Determine the prevalence of Staphylococcus aureus mupirocin resistance in a Neonatal Intensive Care Unit (NICU) population to inform decolonization regimen decisions. Investigate highly resistant methicillin-resistant S. aureus (MRSA) isolates for stain relatedness and horizontal transmission events.
Methods:
Mupirocin susceptibility of S. aureus isolates from nares of NICU patients was evaluated by E-test. Strain relatedness of nine MRSA isolates with high-level mupirocin resistance along with one blood isolate was analyzed by whole-genome sequencing. An epidemiological investigation was performed using electronic medical record data.
Results:
Overall S. aureus mupirocin resistance was 12.7% (89/102) with MRSA isolates exhibiting a 38% (11/29) resistance rate. All sequenced MRSA isolates were the same strain and possessed the mupA gene. Five patients tested positive on admission, four patients acquired the strain in our NICU, and one patient’s acquisition status was indeterminant.
Conclusions:
Overall, mupirocin resistance among S. aureus isolates was low; however, MRSA isolates demonstrated a higher-than-expected resistance rate. A highly resistant strain was introduced into our NICU and transmitted to several patients, most likely due to a gap in contact precaution implementation. Simplified mupirocin susceptibility testing, clearer interpretation standards and validated alternative therapies for all age groups should be prioritized if mupirocin continues to be nationally recommended and implemented as a decolonization therapy.