DESCRIPTION 
- Methicillin-resistant Staphylococcus aureus (MRSA) has historically been a pathogen endemic within healthcare settings, usually affecting the elderly and chronically ill. This strain of S. aureus has been termed "healthcare-associated MRSA" (HA-MRSA).
- Throughout the past decade, MRSA has become an increasingly common pathogen among younger, healthier populations who do not have a healthcare-related exposure history. This type of MRSA pathogen has been termed "community-acquired MRSA" (CA-MRSA).
- CA-MRSA is the most common cause of skin and soft tissue infections seen in the ED
- While CA-MRSA may cause skin and soft tissue infection, it may also lead to severe multisystem disease, including sepsis and necrotizing pneumonia
Geriatric Considerations
HA-MRSA (see below) is a different genotypic form of MRSA that frequently causes morbidity among the elderly, especially those living within extended-care facilities or those with healthcare-related exposures.
ETIOLOGY
- S. aureus is a gram-positive cocci frequently colonizing the skin
- MRSA refers to a specific strain of S. aureus that has resistance against the antimicrobial properties of numerous antibiotics, including methicillin
- Prisoners, athletes, soldiers, children in daycare, IV drug users, and those with prior treatment for MRSA or exposure to MRSA are at highest risk for colonization and subsequent infection.
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SIGNS AND SYMPTOMS
History
- Skin and soft tissue infections:
- Increasing redness
- Pain
- Warmth
- Swelling
- Fever
- Chills
- Malaise
- Sepsis/pneumonia:
- Inquire about prior diagnosis of MRSA infections, MRSA exposures, and family members or close contacts with a history of MRSA, as such a patient is at risk for CA-MRSA infection.
Physical Exam
- Skin and soft tissue infections:
- Abscess: Tender, raised boil with underlying induration and fluctuance
- Cellulitis: Warm erythema possibly with lymphangitic streaking
- Sepsis:
- Vital sign abnormalities including tachycardia and hypotension, respiratory failure, mental status changes, petechiae, systemic signs of toxicity
- Pneumonia:
- Tachypnea, crackles, retractions, hypoxia
- Alveolar opacities on chest radiographs
Pediatric Considerations
MRSA is the leading cause of skin and soft tissue infections among children presenting to the emergency department.
ESSENTIAL WORKUP
- Abscess:
- I&D with packing and prompt follow-up is warranted for abscess
- Microbiology often performed for antibiotic sensitivity given the changing antimicrobial resistance patterns
- Sepsis:
- Source identification, including blood culture/urine culture, CXR, is indicated as resuscitation begins
- Pneumonia:
- Chest radiographs and continuous vital sign monitoring is indicated
DIAGNOSIS TESTS & INTERPRETATION
Lab
- Skin and soft tissue infections:
- Bacterial culture is often warranted to monitor for CA-MRSA resistance patterns
- Sepsis and pneumonia:
- Blood, urine, and body fluid cultures. CBC, CMP to assess for organ dysfunction
Imaging
- Bedside US:
- Abscess: Anechoic fluid collection
- Cellulitis: "Cobblestoning" within the soft tissue
- CXR:
- Indicated for patients with presumed sepsis, systemic illness, or pneumonia
Diagnostic Procedures/Surgery
Cultures of skin and soft tissue infections are frequently obtained to monitor microbiology and antimicrobial resistance patterns should a patient fail a course of therapy.
DIFFERENTIAL DIAGNOSIS
ALERT
Empiric antimicrobial treatment of skin and soft tissue infections should cover for common skin pathogens beyond MRSA (i.e., streptococcus)
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PRE-HOSPITAL
- Contact precautions for all providers if MRSA is suspected
- IV access and fluid resuscitation if sepsis is suspected
INITIAL STABILIZATION/THERAPY
Begin resuscitation and administer early empiric antibiotics if pneumonia, fasciitis, or sepsis is suspected:
- Include early coverage with antibiotics effective against MRSA
ED TREATMENT/PROCEDURES
- Skin and soft tissue infections:
- Abscess:
- I&D with packing
- Antibiotics may not be necessary if there is no evidence for deep tissue infection or cellulitis
- Cellulitis:
- Cellulitis caused by CA-MRSA in a healthy, well-appearing patient may be treated with oral antibiotics in the outpatient setting
- Ill appearing patients, patients with underlying medical conditions, and patients failing outpatient therapy require IV antibiotics with coverage against CA-MRSA
- Sepsis and pneumonia:
- Early administration of broad-spectrum antibiotics that cover against MRSA should be given promptly if the patient is at risk for CA-MRSA
MEDICATION
ALERT
Review antimicrobial resistance patterns of CA-MRSA within your community prior to choosing a specific antibiotic regimen, as many antibiotics listed below may not be 100% effective against CA-MRSA.
First Line
- Bactrim:
- Adults: Bactrim DS 160/800 PO BID
- Children: 10 mg/kg PO BID
- Clindamycin:
- Adults: 150–450 mg PO QID
- Children: 5 mg/kg PO/IV TID–QID
- Doxycycline:
- Adults: 100 mg PO BID
- Children: 2.2 mg/kg PO BID
- Vancomycin:
- Adults: 1 g IV q8–12h
- Children: 15 mg/kg IV q8–12h
Second Line
- Rifampin:
- Should not be used as monotherapy due to inducible resistance
- Adults: 300 mg PO BID
- Children: 10–20 mg/kg/d in 2 div. doses PO for 5 days; not to exceed 600 mg/d
- Linezolid:
- Adults: 600 mg PO/IV q12h
- Children: 10 mg/kg PO/IV q8h
Pregnancy Considerations
Avoid the use of tetracyclines in pregnancy
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DISPOSITION
Admission Criteria
- Patients with signs/symptoms of bacteremia, progressive infection, or systemic illness should be admitted:
- Fever, chills, lymphangitic streaking
- Patients with underlying comorbid diseases such as diabetes or immunodeficiency should be admitted
- Individuals who have failed a course of outpatient therapy should be admitted and given IV antibiotics effective against MRSA
Discharge Criteria
Healthy, well-appearing patients with simple skin and soft tissue infections may be followed in the outpatient setting.
Issues for Referral
MRSA infection refractory to multiple medications may require infectious disease consultation.
FOLLOW-UP RECOMMENDATIONS
- All skin and soft tissue infections should be re-evaluated within 24–48 hr to monitor for clinical improvement.
- Individuals failing outpatient therapy require hospital admission and IV antibiotics.
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ICD9
041.12 Methicillin resistant Staphylococcus aureus in conditions classified elsewhere and of unspecified site
ICD10
- A41.02 Sepsis due to Methicillin resistant Staphylococcus aureus
- A49.02 Methicillin resis staph infection, unsp site
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- Frazee BW, Lynn J, Charlebois ED, et al. High prevalence of methicillin-resistant Staphylococcus aureus in emergency department skin and soft tissue infections. Ann Emerg Med. 2005;45:311–320.
- Klevens RM, Morrison MA, Nadle J, et al. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA. 2007;298:1763–1771.
- Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med. 2006;355:666–674.
- Odell CA. Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infections. Curr Opin Pediatr. 2010;22:273–277.
- Wallin TR, Hern HG, Frazee BW. Community-associated methicillin-resistant Staphylococcus aureus. Emerg Med Clin North Am. 2008;26:431–455.
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