Genomic Analysis of MRSA for Evaluating Local Transmission Dynamics in Geriatric Long-Term Care Facilities in Japan

Area of Science:

• Infectious Diseases
• Genomics
• Epidemiology

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) colonization is a significant global health issue, particularly in geriatric long-term care facilities (LTCFs).
• Understanding MRSA transmission dynamics among residents in Japanese LTCFs is crucial for effective control but remains largely uncharacterized.

Purpose of the Study:

• To investigate the transmission dynamics of MRSA among residents in Japanese geriatric LTCFs using whole-genome sequencing.
• To identify genomic clusters of MRSA and determine the timing of acquisition (within or before facility admission).

Main Methods:

• Whole-genome sequencing of 85 MRSA isolates from 76 residents across 4 Japanese LTCFs.
• Single-nucleotide polymorphism (SNP) analysis to define transmission clusters (≤15 core-genome SNP distance).
• Antimicrobial susceptibility testing and resistance gene analysis.

Main Results:

• Of 76 MRSA-colonized residents, 34 (44.7%) were part of 14 distinct genomic clusters.
• Three residents acquired MRSA strains within the LTCFs, while 14 residents admitted recently carried strains already belonging to genomic clusters, indicating pre-admission transmission.
• Prevalent MRSA strains showed susceptibility to trimethoprim-sulfamethoxazole and resistance to levofloxacin and clindamycin.

Conclusions:

• MRSA transmission in Japanese LTCFs occurs both within the facility and prior to resident admission.
• Findings emphasize the necessity of comprehensive MRSA transmission mitigation strategies extending beyond LTCF boundaries.