Community Associated Methicillin-Resistant Staphylococcus Aureus: A Review

Michael J. Rybak, PharmD; Kerry L. LaPlante, PharmD

Disclosures

Pharmacotherapy. 2005;25(1):74-85. 

In This Article

Outbreaks

Outbreaks of CA-MRSA were first described in the early 1980s.[7,50,51] In the late 1990s, increasing reports began to emerge.[18,24,48,52,53,54,55,56,57,58,59,60] Unfortunately, CA-MRSA is now a common community-based pathogen. It has demonstrated great geographic diversity, with outbreaks reported in the Unites States, Canada, Europe, Finland, Saudi Arabia, India, Asia, Australia, and New Zealand.[24,25,53,54,59,61,62,63,64,65,66,67] The strains involved in these outbreaks have in common the mec type IV cassette but are genetically distinct from one another. Outbreaks of CA-MRSA are typically characterized by clusters of skin and soft tissue infections among persons who have close contact with one another. Most concerning is that persons infected are otherwise healthy individuals with no known risk factors for infection by drug-resistant bacteria.

The first report of CA-MRSA came from a large urban Michigan hospital in 1982.[68] It described community-associated S. aureus infections in 24 intravenous drug users and 16 nonusers. All persons infected were otherwise healthy individuals with no risk factors for MRSA colonization. On the basis of PFGE data, investigators proposed that MRSA infection arose in the community as well as in the hospital and had the potential to disseminate in both settings. It has been subsequently noted that intravenous drug users have frequent contact with health care institutions, and the strains they are colonized with may have originated in the hospital.

During the 1980s and through the mid 1990s, CA-MRSA infections were infrequent in populations other than intravenous drug users. However, in October 2001, the Mississippi State Department of Health notified the CDC that 31 prison inmates had acquired MRSA skin or soft tissue infections.[56] This number was unexpectedly high for a non-health care setting. The next year, inmates in the Los Angeles County Jail began reporting a high frequency of spider bites. Further investigation revealed that these so-called "bites" were actually MRSA skin infections. Also that same year, the Los Angeles County Department of Health Services investigated cases of invasive MRSA infection in two athletes on the same team who were hospitalized. In addition, outbreaks among men having sex with men were also reported.[56] In 2003, researchers described an outbreak of MRSA skin infections among a military beneficiary population.[69] An additional study reported CA-MRSA infections in roommates sharing instruments used for plucking and trimming hair.[70] These reports of invasive MRSA skin infections emphasized the potential for rapid spread of the organism within the community among individuals who may acquire it through close personal contact.[56,71,72]

Children are also vulnerable to CA-MRSA. One of the first major reports of invasive CA-MRSA infections occurred in Minnesota and North Dakota between 1997 and 1999. This outbreak was associated with four pediatric deaths from infections that progressed to pneumonia and sepsis syndrome.[73]

Humans are not the only hosts for CA-MRSA, which has raised concern as a possible emerging zoonotic and veterinary disease. A report in 2003 discussed a common clonal mec type IV strain isolated from horses and their caretakers at an equine farm in Ontario. Horses are not known to harbor S. aureus naturally. Based on timing of isolation, subtyping, and evaluation of animal and human contact, combinations of horse-human, human-horse, or horse-horse transmission were suspected.[74]

Few surveillance studies have characterized how this pathogen develops within the community. One research group conducted S. aureus surveillance during an outbreak in a rural Alaska village that is not connected to other villages by roads.[46] The researchers used PFGE and PVL production to identify the relatedness of the isolates. They discovered that patients living in a community associated with an outbreak had received more antibiotic courses during the past 12 months then patients in a nonoutbreak setting (p=0.01). Also, individuals involved in the outbreak were more likely to use a sauna that was known to be colonized by MRSA. The investigators determined that the likely cause for MRSA colonization was the sauna's plywood, which was semiporous and had an irregular shape that allowed for biofilm formation attachment and hence MRSA survival at high temperatures.

Due to the rise in CA-MRSA outbreaks, the CDC has published recommendations to prevent the spread of MRSA among persons living in the same household.[30] These recommendations include covering infections that drain or produce pus, washing hands frequently, avoiding the sharing of personal items (e.g., towels, washcloth, razor, clothing, or uniforms), washing soiled linens and clothes with hot water, and drying clothes in a hot dryer rather than air-drying.

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