The clinical characteristics and molecular epidemiology of methicillin‐resistant Staphylococcus aureus ( MRSA ) among very elderly people in Japan

AimMethicillin‐resistant Staphylococcus aureus (MRSA) is a major nosocomial infection‐causing pathogen. The clonal shift from staphylococcal cassette chromosome mec (SCCmec) type II MRSA to SCCmec type IV MRSA has occurred rapidly in acute‐care hospitals. However, the epidemiology and clinical impacts of MRSA in geriatric hospitals are poorly documented. We performed a molecular epidemiological analysis of the clinical isolates and retrospectively investigated the clinical characteristics of SCCmec type IV MRSA in elderly individuals.MethodsMRSA isolates were grouped according to the SCCmec type and virulence genes (tst, sea, seb, sec, and lukS/F‐PV), and multi‐locus sequence typing (MLST) was performed.ResultsOf the 145 MRSA isolates obtained from patients with a median age of 85 years, 100 (69.0%) were obtained from sputum samples, 22 (15.2%) from skin and soft tissues, and seven (4.8%) from blood samples. The most prevalent clone was SCCmec type IV/clonal complex (CC)1/sea+ (59.3%), followed by SCCmec type I/sequence type (ST) 8 (17.3%). Of the 17 (11.7%) strains to which an anti‐MRSA drug was administered by a physician, only three were SCCmec type IV/CC1/sea+ (17.6%) and five were SCCmec type I/ST8 (29.4%). SCCmec type IV/CC1/sea+ MRSA was more frequently isolated in long‐term care wards than were SCCmec type I/ST8 strains (odds ratio: 2.85, 95% confidence interval: 1.08–7.54) and was less frequently treated as the cause of MRSA infections (odds ratio: 0.15, 95% confidence interval: 0.03–0.73).ConclusionsSCCmec type IV/CC1/sea+ MRSA was the predominant clone and could be easily transmissible and be capable of colonization. Geriatr Gerontol Int 2023; 23: 744–749.