Community Acquired Methicillin Resistant
Staphylococcus aureus
This article on Community Acquired methicillin resistant S.aureus was originally printed in the September 2006 issue of doctorsNS. We thank the editor and authors for their permission the republish this article.
Over the past three decades the medical community has seen the emergence and spread of strains of S. aureus that display resistance to betalactams (such as cloxacillin and the cephalosporins), and the carbapenems (such as imipenem, meropenem and ertapenem). In this update some recent changes in the clinical pattern of S aureus infections that are important for the practitioners are reviewed.
What is HAMRSA?
In the 1980's it was noted that some hospital strains of S. aureus were resistant to methicillin/cloxacillin. These bacteria were labeled methicillin resistant S. aureus or MRSA. Studies show that these hospital acquired MRSA (HAMRSA) are multi-resistant, usually also demonstrating resistance to macrolides, clindamycin, and fluorquinolones. In most clinical situations, vancomycin is required for the treatment of HAMRSA infections. The prevalence of this bacteria has increased over the years, but they are transmitted primarily in the hospital setting, where special precautions are taken to prevent its spread. As the provision of health care moves more into the community, there has been some movement of HAMRSA into the "out of hospital" setting. Surprisingly, however, the community prevalence of HAMRSA remains remarkably low.
What is CAMRSA?
CAMRSA (community acquired MRSA) occurs when an individual becomes colonized or infected with MRSA, but has not acquired the infection in the health care setting or from someone harbouring MRSA. The CAMRSA organism is genetically different from the HAMRSA. These infections have been seen in the United States, aboriginal communities in the northern Canadian prairie provinces, and in Europe. There have been only a half dozen CAMRSA isolates identified to date in Nova Scotia.
Is CAMRSA different from other infections caused by Staph aureus?
Clinical and laboratory studies have shown that CAMRSA differs in several ways from HAMRSA. CAMRSA, genetically distinct from HAMRSA, is more likely to carry the genes for a factor (Panton-Valentine leukocidin) believed to make these strains potentially more virulent. CAMRSA has a propensity to cause severe soft tissue infections and pneumonia, especially in young children and young adults. Because close contact is required for transmission, outbreaks have been seen in sorts teams, correction facilities, and among family members. Other people at risk for CAMRSA are injection drug users and the homeless. CAMRSA is usually susceptible to clindamycin, doxycycline, and trimethoprim/sulfamethoxazole.
How should physician's practices change?
Early recognition of the emergence of CAMRSA in a community requires vigilance on the part of primary care physicians, laboratories, and public health officials. Obtaining good culture material for susceptibility testing is important to help to identify the appropriate antimicrobial therapy, if required.
This also allows the laboratory to identify trends in S.aureus antibiotic susceptibility. Since MRSA is a reportable infection, Public Health will also be able to track whether CAMRSA is increasing in the community.
One thing that physicians can do is submit abscess material for culture, especially in the setting of soft tissue infection, treatment failure, when there appear to be outbreaks of skin and soft tissue infection among close contacts. Clinical follow-up to assess the response to therapy is even more important with the appearance of CAMRSA.
Given the infrequent appearance, so far, in Nova Scotia, empiric antibiotic choices for skin infections should not change. If the lab reports MRSA from a clinical specimen, antibiotics should be chosen according to the reported susceptibility pattern. Apart from different antimicrobial choices for CAMRSA, management of this strain in the community is the same as for other S.aureus infections: good personal and home hygiene, good hand hygiene when caring for patients and appropriate would care.
Lynn Johnston and Joanne Langley
References:
Chambers HF. The changing epidemiology of Staphylococcus aureus? Emerg Infect Dis 2001;7:178=82 (Level 3 evidence)
Conly JM, Johnston BL The emergence of methicillin-resistant Staphylococcus aureus as a community acquired pathogen in Canada. Can J Infect Dis 2003;14:249-51
Kaplan SL. Treatment of community-associated methicillin resistant Staphylococcus infections. Ped infect Dis J 2005; 24:457-8 (Level 5 evidence)
Nicolle N. Community-acquired methicillin-resistant Staphylococcus aureus: Getting over it. Can J Infect Dis and Med Microbiol 2005; 16:323-4
You can search for abstracts of the above references by following this link: PubMed
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