According to Otter et al. (J Hosp Infect 2011), CA-MRSA can be categorized by epidemiologic criteria, antibiotic susceptibility pattern and molecular approach. The latter seems to be more precise, but according to Mediavilla et al. (Curr Opin Microbiol 2012) we have CA- clones among SCCmec type I and II. Also, some pandemic CCs have both CA- and HA- isolates. I think none of the mentioned criteria can completely define CA-MRSA. Does anyone have another opinion?
Community-associated MRSA infections (CA-MRSA) as opposed to Hospital-associated or Healthcare-associated MRSA (HA-MRSA) are MRSA infections in otherwise healthy idnividuals who have not had a medical procedure, not been in a healthcare environment or who have not been hospitalized in the recent past. I think the CDC defines recent past as one year.
Shannon is basically right; the distinction is made on epidemiologic criteria. From the Disease Control Newsletter (2004); 32:61–72 (http://www.health.state.mn.us/divs/idepc/newsletters/dcn/2004/0406dcn.pdf):
In an attempt to standardize the definition of CA-MRSA, the Centers for Disease Control and Prevention (CDC) Active Bacterial Core Surveillance (ABCs) sites (Connecticut, Georgia, Maryland, and Minnesota), which have conducted surveillance for CA-MRSA since 2001, define CA-MRSA as MRSA that has been isolated from patients who have no history of
1) positive culture for MRSA from any body site obtained more than 48 hours after admission to a hospital (if hospitalized);
2) prior MRSA infection or colonization;
3) hospitalization, surgery, residency in a long-term care facility, hemodialysis, or peritoneal dialysis within the past year; or
4) current indwelling percutaneous devices or catheters.
Refer: Lindsay Nicolle. 2006 Community-acquired MRSA: a practitioner's guide.CMAJ
vol. 175 no. 2
Thanks for your comments. The criteria proposed by CDC is widely used by researchers. However, there is an accumulating literature suggesting that CDC criteria may underestimate CA-MRSA prevalence. Otter et al. (J Hosp Infect 2012; 81:143-148) mentioned some of the limitations of epidemiological criteria. For example, by using epidemiological criteria:
1) community-associated, hospital-onset MRSA may be misclassified as HA-MRSA.
2) infections among injecting drug user/homeless group may always be classified as HA-MRSA (because these patients often have a history of hospital admission for another reason).
About the comment by "Dr Zulfgiqar Mirani":
Thanks, but I think CA-MRSA has evolved in the past 10 years and previous criteria (such as the one you mentioned) cannot fully differentiate CA from HA. Even introduction of the term (HACO; health care-associated, community-onset) doesn't seem to solve this problem (David, Clin Microbiol Rev 2010; access link:http://cmr.asm.org/content/23/3/616.full.pdf).
It seems that there is not an agreement for definition of CA-MRSA among leading researchers in this field. Some advocate genotypic approach (e.g. Otter, JHI 2012) but some consider it as an impractical tool for clinicians. The obvious point is that current CDC criteria needs some improvements.
It's likely that the CDC definition does underestimate CA-MRSA prevalence. The definition seems designed to minimize false CA-MRSA positives, at the risk of producing false negatives. I think this is common with working definitions for newly recognized, or poorly understood diseases.
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