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Unit % Patients (95% confidence interval)
1999 2000 2001 2002 2003 2004 2005 2006
   All MRSA 26.8
   HA-MRSA 23.2
      Blood 2.7 2.8 4.0 3.7 3.1 2.8 2.1 1.9
      Lungs 4.7 5.3 6.5 5.5 5.4 4.2 3.5 2.9
      Skin 9.3 10.6 10.1 11.6 13.8 15.5 14.2 15.5
      Other source 6.4 6.5 7.6 7.7 7.0 6.0 4.2 4.0
   CA-MRSA 3.6
      Blood 0.3 0.3 0.6 0.7 0.8 0.8 0.9 0.8
      Lungs 0.4 0.5 0.9 0.9 0.7 0.6 0.8 0.7
      Skin 2.3 3.0 2.9 4.8 9.0 16.6 25.3 25.4
      Other source 0.5 0.5 0.8 0.9 1.0 1.3 1.6 1.4
   All MRSA 46.7
   HA-MRSA 43.4
      Blood 7.1 7.2 7.5 7.5 7.5 7.0 6.2 6.3
      Lungs 21.4 19.9 19.2 18.5 17.6 16.5 14.7 14.5
      Skin 9.3 10.5 11.4 12.0 12.9 13.1 13.0 13.1
      Other source 5.6 5.6 6.0 5.9 6.1 5.3 4.5 4.7
   CA-MRSA 3.3
      Blood 0.6 0.7 1.0 1.2 1.2 1.7 2.1 2.0
      Lungs 1.2 1.6 2.1 2.3 2.1 2.6 3.3 3.8
      Skin 1.1 1.7 2.1 4.0 6.6 10.9 14.4 12.8
      Other source 0.4 0.5 0.7 0.9 1.0 1.2 1.3 1.2

Frequency of MRSA in Hospitals, by Unit, United States, 1999-2006*

*MRSA, methicillin-resistant Staphylococcus aureus; HA-MRSA, hospital-associated MRSA; CA-MRSA, community-associated MRSA.
Data through October only. Data for blood, lungs, skin, and other source refer to the percentage of each source tested that was estimated to be CA-MRSA or HA-MRSA.


Community-Associated Methicillin-Resistant Staphylococcus aureus in Outpatients, United States, 1999-2006

  • Authors: Eili Klein, MA; David L. Smith, PhD; Ramanan Laxminarayan, PhD, MPH
  • CME Released: 11/23/2009
  • Valid for credit through: 11/23/2010
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Target Audience and Goal Statement

This activity is intended for primary care physicians, infectious disease specialists, and other physicians who care for patients at risk for infection with methicillin-resistant Staphylococcus aureus (MRSA).

The goal of this activity is to describe the recent epidemiology of infection with methicillin-resistant Staphylococcus aureus (MRSA).

Upon completion of this activity, participants will be able to:

  1. Specify characteristics of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) compared with hospital-acquired MRSA
  2. Recognize recent trends in MRSA among outpatients
  3. Identify anatomic sites most commonly associated with infection with MRSA resistant only to oxacillin
  4. Recognize recent trends in MRSA among inpatients


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Medscape, LLC encourages Authors to identify investigational products or off-label uses of products regulated by the US Food and Drug Administration, at first mention and where appropriate in the content.


  • Eili Klein, MA

    Princeton University, Princeton, New Jersey


    Disclosure: Eili Klein, MA, has disclosed no relevant financial relationships.

  • David L. Smith, PhD

    University of Florida, Gainesville


    Disclosure: David L. Smith, PhD, has disclosed no relevant financial relationships.

  • Ramanan Laxminarayan, PhD, MPH

    Resources for the Future, Washington, DC; Princeton University, Princeton, New Jersey


    Disclosure: Ramanan Laxminarayan, PhD, MPH, has disclosed no relevant financial relationships.


  • Thomas Gryczan

    Technical Writer-Editor, Emerging Infectious Diseases


    Disclosure: Thomas Gryczan has disclosed no relevant financial relationships.

CME Author(s)

  • Charles P. Vega, MD

    Associate Professor and Residency Director, Department of Family Medicine, University of California-Irvine, Irvine California


    Disclosure: Charles P. Vega, MD, has disclosed no relevant financial relationships.

CME Reviewer(s)

  • Sarah Fleischman

    CME Program Manager, MedscapeCME


    Disclosure: Sarah Fleischman has disclosed no relevant financial relationships.

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    For Physicians

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Community-Associated Methicillin-Resistant Staphylococcus aureus in Outpatients, United States, 1999-2006

Authors: Eili Klein, MA; David L. Smith, PhD; Ramanan Laxminarayan, PhD, MPHFaculty and Disclosures

CME Released: 11/23/2009

Valid for credit through: 11/23/2010


Abstract and Introduction


Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has become a major problem in US hospitals already dealing with high levels of hospital-associated MRSA (HA-MRSA). Using antimicrobial drug susceptibility data for 1999-2006 from The Surveillance Network, we characterized the relationship between outpatient and inpatient levels of CA-MRSA nationally. In outpatients, the frequency of CA-MRSA isolates has increased >7× during 1999-2006, which suggests that outpatients have become a major reservoir for CA-MRSA. However, contrary to results in other reports, although CA-MRSA increases are associated with decreases in the frequency of HA-MRSA in hospitals, the decreases are only modest. This finding suggests that instead of replacing HA-MRSA in the hospital, CA-MRSA is adding to the overall presence of MRSA already found within the hospital population.


The past decade has seen a large increase in infections with hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA).[1] MRSA is one of the most common causes of nosocomial infections, especially invasive bacterial infections,[2] and is now endemic and even epidemic to many US hospitals, long-term care facilities,[3] and communities.[4-6] Although community-associated MRSA (CA-MRSA) strains have been recognized as a leading cause of skin and soft tissue infections,[1,6] especially in patients with no established healthcare risk factors,[7,8] they also cause severe invasive infections.[9,10] Recent reports based on genotypic evidence have suggested that CA-MRSA is likely spreading within hospitals as well, blurring the line between CA-MRSA and HA-MRSA infections.[11]

Molecular typing studies have identified 2 MRSA clones, USA300 and USA400, as the primary types that cause CA-MRSA infections (12). Evidence suggests that emergence of these strains was independent of hospital strains.[13] Thus, understanding the role of outpatients, who are among the likely carriers of CA-MRSA into a hospital, is useful for understanding the changing epidemiology of MRSA in hospitals. Outpatients, who outnumber inpatients by ≈3:1, may play a major role in the spread of CA-MRSA strains from the community to the hospital through their interaction with hospital staff or use of similar hospital resources, such as surgical rooms. However, limited information hinders understanding of long-term trends in CA-MRSA in outpatients in the context of changing epidemiology of inpatients. This lack of information hinders the ability to evaluate infection control methods in the face of a possible emerging epidemic of nosocomial infections caused by CA-MRSA.

Knowledge of trends in antimicrobial drug resistance rates for emerging pathogens are useful to clinicians to ensure high-quality care, which is essential for antimicrobial drug therapy, in which different drugs can have different costs and effectiveness. These trends can also help hospital administrators and policy makers make infection control investments to address the role that large influxes of outpatients with CA-MRSA infections may play with regard to overall MRSA infection rates in the hospital.

Table of Contents

  1. Abstract and Introduction
  2. Methods
  3. Results
  4. Discussion