Friday, December 28, 2012

Study: Weighing The Risks Of MRSA Colonization

colorized scanning electron micrograph (SEM) of MRSA

MRSA - Photo Credit CDC

# 6807


The CDC tells us, in their Definition of MRSA page, that:


While 25% to 30% of people are colonized* in the nose with staph, less than 2% are colonized with MRSA (Gorwitz RJ et al. Journal of Infectious Diseases. 2008:197:1226-34.).

When a person carries the organism/bacteria but shows no clinical signs or symptoms of infection. For Staph aureus the most common body site colonized is the nose.



Although 2% doesn’t sound like a lot, there are signs that number may be increasing. Once considered primarily a hospital acquired infection, CA-MRSA (community acquired) is growing in incidence.


As an example, in Firefighters & Paramedics At Greater Risk Of MRSA and Firefighters & MRSA Revisited we looked at research showing a 10x’s greater incidence of MRSA colonization (20%) among a sampling of firefighters tested in Washington State.


Since one person’s colonization can become another person’s infection, topics of debate have included:


  1. What risks are there to the individual from long-term colonization?
  2. What risks are there to others In the Community or a household?
  3. What risks are there to others in a hospital or long-term care environment?
  4. What (if any) steps should be taken to decolonize carriers, and in what setting (hospital admission? Outpatient?) is decolonization desirable and effective?


There are, it seems, few easy answers. 


Mary McKenna, editor of the terrific Superbug Blog, took a look at the problems inherent with the decolonization of MRSA carriers in 2009 with:


Decolonization: disappointing news 

The upshot was that while studies have shown that decolonization procedures on hospitalized patients about to undergo surgery can reduce infections, the value to other patients is far less clear.


And as Maryn points out, overuse of mupirocin – the primary antibiotic used to decolonize patients –can lead to increased resistance over time.


And Mary also tells of a paper published in Infection Control and Hospital Epidemiology, that evaluated the success of decolonization protocols in 3 major Illinois hospitals, that less than reassuring results: a temporary reduction in patients’ being colonized with MRSA, but no success in preventing infection.


In 2011, the Infectious Diseases Society of America published their clinical practice guidelines for treating MRSA in adults and children, where they endorse `decolonization’, but only under select scenarios (note SSTI = Skin & Soft Tissue Infection):


  • 14. Decolonization may be considered in selected cases if:

    • i. A patient develops a recurrent SSTI despite optimizing wound care and hygiene measures (C-III).

    • ii. Ongoing transmission is occurring among household members or other close contacts despite optimizing wound care and hygiene measures (C-III).


    • ii. Contacts should be evaluated for evidence of S. aureus infection:
    • a. Symptomatic contacts should be evaluated and treated (A-III); nasal and topical body decolonization strategies may be considered following treatment of active infection (C-III).
    • b. Nasal and topical body decolonization of asymptomatic household contacts may be considered (C-III)

    But what, if anything, to do about asymptomatic carriers who are colonized, but not infected with MRSA remains up in the air.


    Hospital strategies to contain and control MRSA range from passive surveillance to aggressive `search & destroy’ policies – with variations in between.


    Passive surveillance – which is the most commonly used protocol in the United States – involves  testing only those who have clinical signs or symptoms of

    Since patients may be colonized without exhibiting outward signs, this will fail to detect a great many carriers of the bacteria.

    Active Surveillance – requires the testing of high risk admissions (ie.  Hx of MRSA, Antibiotic Use, Admission to Hospital in past year, Resident of Long-term care facility, etc.) for the bacteria.

    Patients testing positive may be isolated and decolonized or treated, with strict infection control precautions enforced.

    Universal Surveillance – takes the above steps to a higher level, where all admissions and personnel are routinely swabbed and tested for MRSA.

    “Search & Destroy” – which is the most intensive protocol, has been used successfully in countries like Finland, Denmark and the Netherlands.

    It combines Active or Universal Surveillance with testing of patients in high-risk wards at intervals and prior to discharge.


    The reluctance to adopt the more aggressive of these measures have been the costs, the inconvenience to patients and their visitors, and quite frankly, objections by some hospital staff over being repeatedly tested.

    A recent study appearing in Critical Care Medicine, looked at the effects of a strict S&D policy instituted at a rural trauma center, and found an immediate reduction specific types of HAIs (Hospital Acquired Infections) after implementation.


    Search & Destroy (S&D): Eradication of Mrsa Colonization Is Associated With Decreased Mrsa Infections in Trauma Patients

    Borst, Gregory; Waibel, Brett; Toschlog, Eric; Coogan, Michael; Skarupa, David; Rotondo, Michael; Ramsey, Keith

    Conclusions: Search and destroy is associated with significant decreases in the incidence of MRSA VAP and CLABSI in trauma patients. Decreases in MRSA CAUTI and wound infections were also seen after the implementation of this program. Pre-emptive strategies to identify and eradicate MRSA are worthwhile endeavors in terms of preventing nosocomial infection.


    Despite its critics, S&D policies have often shown reductions in HAIs. 


    Which brings us to another study, published last week in the journal Antimicrobial Agents and Chemotherapy, that finds (among a relatively small cohort of patients) that colonization with MRSA posed a substantial risk of MRSA infection, increased mortality, or readmission to the hospital, compared to patients without MRSA colonization.



    Long-Term Risk for Readmission, Methicillin-resistant Staphylococcus aureus (MRSA) Infection, and Death among MRSA-Colonized Veterans.

    Quezada Joaquin NM, Diekema DJ, Perencevich EN, Bailey G, Winokur PL, Schweizer ML.


    Division of Infectious Diseases.


    Background: While numerous studies assessed outcomes of MRSA colonization over the short term, little is known about longer-term outcomes after discharge. An assessment of long-term outcomes could inform the utility of various MRSA prevention approaches.

    Methods: A matched cohort study was performed among Veterans Affairs (VA) patients screened for MRSA colonization between the years 2007 and 2009 and followed to evaluate outcomes until 2010. Cox proportional hazard models were used to evaluate the association between MRSA colonization and long-term outcomes such as infection-related readmission, and crude mortality.

    Results: 404 veterans were included, 206 of whom were MRSA carriers and 198 who were non-carriers. There were no culture-proven MRSA infections on readmission among the non-carriers, but 13% of MRSA-carriers were readmitted with culture proven MRSA infections on readmission (P<0.01).

    MRSA carriers were significantly more likely to be readmitted, be readmitted more than once due to proven or probable MRSA infections, and be readmitted within 90 days of discharge compared to non-carriers (p<0.05). Infection-related readmission (adjusted hazard ratio [AHR] =4.07; 95% confidence interval [CI]: 2.16, 7.67) and mortality (AHR=2.71; 95% CI: 1.87, 3.91) were significantly higher among MRSA carriers compared to non-carriers, after statistically adjusting for potential confounders.

    Conclusions: Among a cohort of VA patients, MRSA carriers are at high risk of infection-related readmission, MRSA infection and mortality compared to non-carriers. Non- carriers are at very low risk of subsequent MRSA infection. Future studies should address whether interventions such as nasal or skin decolonization could result in improved outcomes for MRSA carriers.

    Although based on a small cohort, this study suggests that being colonized (but not infected) with MRSA is a significant risk factor for future infection, and if these findings can be confirmed by others, may influence how MRSA colonization is viewed in the future.


    Despite some recent improvements in MRSA rates among hospitalized patients in the United States, HAIs (which include many other pathogens) continue to exact a heavy toll. This oft quoted assessment from the CDC on the burden of Hospital Acquired Infections in the United States is from 2010.


    A new report from CDC updates previous estimates of healthcare-associated infections. In American hospitals alone, healthcare-associated infections account for an estimated 1.7 million infections and 99,000 associated deaths each year. Of these infections:

    • 32 percent of all healthcare-associated infection are urinary tract infections
    • 22 percent are surgical site infections
    • 15 percent are pneumonia (lung infections)
    • 14 percent are bloodstream infection

    For more on MRSA, and many other antibiotic-resistant threats, you can do no better than to visit Maryn McKenna’s terrific Superbug Blog, and to read her book Superbug: The Fatal Menace of MRSA . . . which won last year’s  NASW Science in Society Journalism Award.

    You’ll find my review of her book HERE

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