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Medicine in Brief, Cases that Test Your Skills

What’s that rash? Recognize community-acquired MRSA

Vol. 7, No. 9 / September 2008

Some patients at high risk for mental illness—intravenous drug users, prisoners, human immunodeficiency virus-positive patients, and the homeless—also are at risk of community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) infections.1 Because your patients may present with CA-MRSA symptoms, you need a basic understanding of this infection’s risk factors and clinical features to initiate necessary referrals (Table).2


Features of community-acquired MRSA infections

At-risk populations

HIV infection, IV drug users, homeless, men who have sex with men, tattoo recipients, individuals living in close quarters such as group homes or prisons
May affect healthy individuals without risk factors

Clinical presentation

Small, hard, red, painful lesions that resemble a spider bite
Most common: skin infections such as a boil, abscess, or cellulitis
Less common: bone and joint infections, pneumonia


Skin-to-skin contact with infected persons
Sharing personal hygiene items, such as towels, with infected persons
Skin breaks

Symptoms requiring emergent referral

Fever, shortness of breath, hypotension, or other systemic symptoms
Rapidly spreading lesion

Source: Reference 2

Risk factors and transmission

CA-MRSA accounts for 78% of skin and soft tissue infections in emergency rooms.3 Patients typically have no known risk factors for infection or health-related exposures, such as recent hospitalization or employment in a healthcare setting. Persons who have taken antibiotics in the past 12 months are at increased risk.1,3,4

Infection spreads by person-to-person contact. In the community, crowding and sharing personal items also facilitate transmission, which accounts for increased risk among military personnel and athletes in contact sports.1 Therefore, caution psychiatric patients against sharing personal hygiene items, such as towels, and instruct infected patients to keep abscess sites covered at all times. Stress the importance of consistent handwashing.

Infection also may be acquired through a skin abrasion, although many infected patients do not remember having local skin trauma.

Clinical presentation. Unlike diffuse drug eruptions associated with psychotropic hypersensitivity reactions, skin involvement caused by CA-MRSA typically is limited. Patients generally present with a warm, swollen, and erythematous area of skin or a circumscribed abscess involving a hair follicle.1 Often patients attribute symptoms to a recent spider bite or report that a family member or friend has a similar rash or lesion.3

Single lesions on the extremities are common, although multiple “boils” are possible. Fluctuance—a wavelike motion beneath the lesion when pressure is applied—may be present. Fever and chills usually are absent unless the infection is invasive or systemic (Photo). Serious forms of infection—such as impetigo and necrotizing fasciitis—are less common, although the latter has been reported more frequently among IV drug users.1

© 2001-2007 DermAtlas

Warm, swollen, erythematous skin with red papules and plaques with central pustules often on the extremities. Treatment. Although the prognosis for most CA-MRSA skin and soft tissue infections is favorable, serious and potentially life-threatening complications can emerge.1 Most infections can be treated successfully with antibiotics and—when an abscess is present—incision and drainage performed in a primary care physician’s office. Trimethoprim-sulfamethoxazole—a commonly used antibiotic—can decrease serum levels of tricyclic antidepressants and prolong the QT interval. Be aware of this interaction in patients receiving antipsychotics, which also can prolong the QT interval.

Practice Points

  • A single boil, abscess, or small, red, painful lesion suggests a community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infection.
  • Be aware of the clinical presentation of CA-MRSA infections to facilitate necessary referrals to a primary care physician or ER.
  • Educate your patients at risk for CA-MRSA skin infections to protect themselves and avoid transmitting infection to others.

Referral to a primary care physician for further management is appropriate for afebrile patients without a history of immunosuppression who present with localized rash involving 1 extremity. Severe infection with bacteremia or other systemic involvement is possible, especially in patients age ≥65.5 Consider ER referral for patients with:

  • compromised immune systems
  • high fever and/or chills
  • rapidly progressing symptoms
  • signs and symptoms consistent with systemic illness, such as shortness of breath or low blood pressure
  • disease involving >1 extremity or multiple abscesses.

Related resources

Drug brand name

  • Trimethoprim-sulfamethoxazole • Bactrim, Septra


Dr. Hebert reports no financial relationship with any company whose products are mentioned in this article or with manufacturers of competing products.

Dr. Rado receives grant/research support from Neuronetics, Eli Lilly and Company, and Janssen Pharmaceutica.


1. Stryjewski ME, Chambers HF. Skin and soft tissue infections caused by community-acquired methicillin-resistant Staphylococcus aureus. Clin Infect Dis 2008;46:S368-77.

2. Boucher HW, Corey GR. Epidemiology of methicillin-resistant Staphylococcus aureus. Clin Infect Dis 2008;46:S344-9.

3. Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S aureus. infections among patients in the emergency department. N Engl J Med 2006;355:666-74.

4. Kazakova SV, Hageman JC, Matava M, et al. A clone of methicillin-resistant Staphylococcus aureus among professional football players. N Engl J Med 2005;352:468-75.

5. Klevens RM, Morrison MA, Nadle J, et al. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA 2007;298(15):1763-7

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