MRSA in the community setting

MRSA is an increasing infection risk in community health-care settings

• MRSA refers to the resistance of a strain of Staphylococcus aureus to the Beta lactam class of antibiotics (may also be resistant to clindamycin, erythromycin and aminoglycosides)
  • Staphylococcus aureus (S. aureus) is a Gram positive bacterium which is present in the normal flora of the nose in about 25% of individuals
  • S. aureus survives well in the environment, on skin scales and in dust and can be carried transiently on the hands
  • S. aureus can colonise other sites of the body e.g. axilla, perineum, broken skin
• MRSA has been defined as healthcare-associated MRSA and community-acquired MRSA (2)
  • methicillin-resistant Staphylococcus aureus (MRSA)
    • community-associated MRSA (CA-MRSA)
      • MRSA strains isolated from patients in an outpatient or community setting (community onset), or within 48 h of hospital admission (hospital onset)
        • patients also typically have no previous history of MRSA infection or colonization, hospitalization, surgery, dialysis or residence in a long-term care facility within the previous year, and absence of indwelling catheters or percutaneous devices at the time of culture
      • new strains of MRSA have recently emerged that cause infections in community patients who have no previous history of direct or indirect healthcare contact
        • strains have been designated CA-MRSA
          • CA-MRSA strains are genetically and phenotypically distinct from HA-MRSA (healthcare-associated MRSA)
        • overall prevalence of S. aureus strains that carry the gene for Panton-Valentine leucocidin (PVL) production is believed to be <2%, and these are mainly MSSA
          • overall prevalence of CA-MRSA is also presently low worldwide (thought to be <0.5% of all MRSA)
        • typically resemble some strains of methicillin-susceptible S. aureus (MSSA) in being susceptible to a wider range of anti-staphylococcal antibiotics (some are resistant only to ß-lactams), and often produce PVL, a toxin that destroys white blood cells and is a staphylococcal virulence factor
    • HA-MRSA (healthcare-associated MRSA)
      • MRSA strains that are transmitted to and circulate between individuals who have had contact with healthcare facilities. These infections can present in the hospital or healthcare setting (hospital or healthcare onset) or in the community (community onset), for example after hospital discharge
    • note however that the boundaries between HA-MRSA and CA-MRSA are becoming blurred due to the movement of patients and infections between hospitals and the community, and to nosocomial outbreaks of CA-MRSA following admission of colonized or infected patients
  • serious S. aureus infections can be caused by strains that are methicillin-resistant or -susceptible and which may or may not express the pathogenic PVL toxin

Notes:

• consult local infection control guidelines and seek local microbiology advice with respect to local management policies for MRSA

Reference:

• (1) Leeds North East PCT Clinical Governance Group. Guideline for the Management of Patients with MRSA in Community Health Care Settings
• (2) Nathwani D et al. Guidelines for UK practice for the diagnosis and management of methicillin-resistant Staphylococcus aureus (MRSA) infections presenting in the community.J Antimicrob Chemother. 2008 May;61(5):976-94