EMRSA-15

EMRSA-15. It is a major epidemic strain of methicillin-resistant Staphylococcus aureus (MRSA) that emerged in the United Kingdom in the early 1990s. This lineage, characterized as sequence type 22 (ST22) and SCCmec type IV, became one of the most successful and globally disseminated healthcare-associated MRSA clones. Its rapid spread and association with significant morbidity and mortality have made it a focal point for infection control and public health surveillance worldwide.

Characteristics

EMRSA-15 belongs to the clonal complex 22 (CC22) and carries the staphylococcal cassette chromosome mec (SCCmec) type IV element, which confers methicillin resistance. This SCCmec type is relatively small and mobile, potentially aiding its transfer between staphylococcal strains. The lineage often exhibits resistance to multiple non-β-lactam antibiotics, including erythromycin and ciprofloxacin. Genomic studies, such as those conducted by the Wellcome Sanger Institute, have traced its evolution and identified key virulence factors and antimicrobial resistance genes that contribute to its success in hospital settings.

Epidemiology

First identified in the UK around 1991, EMRSA-15 quickly replaced other prevalent strains like EMRSA-16 to become the dominant healthcare-associated MRSA in many National Health Service hospitals. Its epidemic spread was documented across Europe, the Middle East, Asia, and Australasia, making it a truly global pathogen. Surveillance networks like the European Antimicrobial Resistance Surveillance Network (EARSS) and the Centers for Disease Control and Prevention's Active Bacterial Core surveillance have tracked its dissemination. Factors contributing to its spread include inter-hospital patient transfers, international travel, and its ability to colonize healthcare environments and personnel.

Clinical significance

This strain is a leading cause of healthcare-associated infections, including bacteremia, pneumonia, surgical site infections, and skin and soft tissue infections. Outbreaks have been reported in intensive care units, surgical wards, and long-term care facilities, such as those investigated by Public Health England. Infections are associated with increased hospital length of stay, higher healthcare costs, and significant patient mortality. Its ability to cause severe disease was highlighted in reports from institutions like the John Radcliffe Hospital and during nationwide prevalence studies.

Treatment and resistance

Initial therapeutic options were often limited to glycopeptide antibiotics like vancomycin and teicoplanin. However, the emergence of strains with reduced susceptibility to vancomycin (VISA) has complicated management. Later agents, such as linezolid, daptomycin, and ceftaroline, have been used for treatment. The strain's resistance profile typically includes fluoroquinolones, aminoglycosides, and macrolides, as documented in surveillance data from the Clinical and Laboratory Standards Institute and research published in journals like The Lancet and Antimicrobial Agents and Chemotherapy.

Prevention and control

Controlling its spread requires rigorous infection prevention measures. Key strategies include active surveillance cultures, contact precautions for colonized or infected patients, and enhanced environmental cleaning, as advocated by guidelines from the World Health Organization and the Healthcare Infection Control Practices Advisory Committee. The successful reduction of EMRSA-15 rates in the UK, often termed the "Search and Destroy" policy, involved mandatory surveillance and bundle interventions promoted by the Department of Health and Social Care. Decolonization protocols using mupirocin and chlorhexidine are also employed, though mupirocin resistance has been reported.

Category:Staphylococcus Category:Antimicrobial resistance Category:Healthcare-associated infections