Community associated methicillin-resistant Staphylococcus aureus CA-MRSA

Biology

Habitat and transmission: CA-MRSA initially affected people outside of hospitals with no known risk factors for MRSA infection. However, as the epidemic has emerged, CA-MRSA strains are an increasingly common cause of nosocomial infection (Otter, 2011). CA-MRSA like other MRSA strains are commonly found on the axillae, nares and skin of affected individuals. The organism can be transmitted via person-to-person contact, the environment and contaminated items. However, the epidemiology of CA-MRSA may be different to HA-MRSA. There is evidence that CA-MRSA are associated with non-nasal sites of colonisation, infection without proceeding colonisation and an increased importance of fomites in their transmission in community settings (Miller and Diep, 2008). 

Treatment and antibiotic resistance: MRSA is resistant to all beta-lactam antibiotics through the mecA carried on the staphylococcal cassette chromosome mec (SCCmec). HA-MRSA generally have SCCmec types I, II or III, however CA-MRSA has been shown to have SCC mec type IV/V (David and Daum, 2010). As a result, CA-MRSA is often susceptible to classes of antibiotics other than b-lactams, as opposed to HA-MRSA strains which are only susceptible to glycopeptides and newer anti-staphylococcals. However, as CA-MRSA have had increased contact with healthcare facilities, multiresistance has begun to emerge (Diep et al., 2008).

Prevention and control: CA-MRSA affects groups of people such as athletes, prisoners, military personnel, ethnic minorities, HIV patients, the homeless and drug users. Risk factors for transmission include crowded conditions, poor sanitation and intravenous drug usage. In order to reduce transmission strict hand-washing should be employed, towels and razors should not be shared and linens should be changed and washed regularly. As CA-MRSA begin to cause more outbreaks and endemic infections in healthcare facilities, standard MRSA control policies may need to be modified to prevent and control the transmission of CA-MRSA strains (Otter 2011).

Symptoms/Effects

Disease and symptoms: Symptoms of CA-MRSA are often similar to that of MSSA infection, which can include relatively benign infections such as impetigo, cellulitis, furuncles and boils to severe infections of the bone, endocarditis, sepsis and toxic shock. However, CA-MRSA has been known to cause invasive skin and soft tissue infections (SSTI). CA-MRSA is also associated with development of diseases such as purpura fulminans, necrotising pneumonia and increasingly necrotising fasciitis (Cataldo et al., 2010). Although Panton-valentine leukocidin (PVL) is thought to play a key role in the virulence of CA-MRSA infections, other virulence factors may well play a role (Cataldo et al., 2010; David and Daum, 2010).

Technical

References:
Cataldo M.A., Taglietti F. And Petrosillo N. (2010) Methicillin-resistant Staphylococcus aureus: A community health threat. Postgrad med. 122(6): 16-23.

David M.Z. and Daum R.S. (2010) Community-associated Methicillin-resistant Staphylococcus aureus: Epidemiology and clinical consequences of an emergic epidemic. Clin Microbiol Rev. 23(3): 616-687.

Diep B.A., Chambers H.F., Graber C.J. et al. (2008) Emergence of multidrug-resistant, community-associated, methicillin-resistant Staphylococcus aureus clone USA300 in men who have sex with men. Ann Intern Med. 148: 249-257.

Miller L.G., Diep B.A. (2008) Clinical practice: colonization, fomites, and virulence: rethinking the pathogenesis of community-associated methicillin-resistant Staphylococcus aureus infection. Clin.Infect.Dis. 2008; 46: 752-760.

Otter J.A., French G.L. (2011) Community-associated meticillin-resistant Staphylococcus aureus strains as a cause of healthcare infection. J Hosp Infect. doi: 10.1016/j.jhin.2011.04.028.