Methicillin-resistant Staphylococcus aureus (MRSA)

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Last reviewed: 14 Apr 2025

Last updated: 31 May 2024

MRSA is an important cause of infection in both healthy people in the community and in patients in healthcare institutions.

It is important to distinguish MRSA colonization from infection.

Healthcare-associated MRSA infections and community-associated MRSA infections exhibit important differences in antibiotic susceptibility.

Community-associated MRSA most commonly results in skin and soft-tissue infections and therapy can often be with oral antibiotics.

Healthcare-associated MRSA infections usually require treatment with intravenous antibiotics.

Isolation of patients with MRSA, through contact precautions, may help to prevent spread of infection.

Definition

MRSA is a type of Staphylococcus aureus that is resistant to most beta-lactam antibiotics, antistaphylococcal penicillins (e.g., methicillin, oxacillin), and cephalosporins. Methicillin resistance is defined as an oxacillin minimum inhibitory concentration of ≥4 micrograms/mL.[1] Oxacillin is in the same class as methicillin and was chosen as the agent for testing of S aureus sensitivity in the early 1990s. Methicillin is still used to describe resistance because of its historical role.[2] MRSA infections can include syndromes of bacteremia, pneumonia, endocarditis, joint infections, and skin or soft-tissue infections.

History and exam

Key diagnostic factors

erythematous skin lesions or pustules, in single or multiple forms
irritation or pain at indwelling catheter site
heart murmur and other signs of endocarditis

Full details

Other diagnostic factors

infection unresponsive to penicillins
history of a presumed spider bite
abscess formation
fever
fatigue
tachycardia and hypotension
shortness of breath and cough
painful urination, hematuria, or urinary retention
night sweats or chills
altered mental status
signs of pulmonary consolidation
abdominal pain or flank pain
joint pain
joint swelling

Full details

Risk factors

age >50 years (healthcare-associated)
children and younger adults <35 years (community-associated)
men who have sex with men (community-associated)
intravenous drug users (community-associated)
indwelling device or current wound (healthcare-associated)
hospitalization within the last year (healthcare-associated)
chronic illness requiring healthcare visits (healthcare-associated)
crowded conditions/semi-closed communities (healthcare-associated and community-associated)
previous history of MRSA (healthcare-associated and community-associated)
exposure to an MRSA-positive person (healthcare-associated and community-associated)
nasal colonization with MRSA (healthcare-associated and community-associated)
prior antibiotic use (healthcare-associated and community-associated)
HIV infection (community-associated and healthcare-associated)

Full details

Diagnostic tests

1st tests to order

CBC
blood culture
urine culture
tissue culture
sputum culture
echocardiogram
CXR
arthrocentesis fluid culture
indwelling vascular catheter tip culture

Full details

Tests to consider

polymerase chain reaction (PCR)

Full details

Treatment algorithm

ACUTE

skin and soft-tissue infection: community-associated

skin and soft-tissue infection: healthcare-associated

bacteremia

pneumonia

visceral abscess

endocarditis

septic arthritis

urinary tract infection (UTI)

osteomyelitis

ONGOING

recurrent skin and soft-tissue MRSA infections in colonized patients

Contributors

Authors

Kyle J. Popovich, MD MS

Professor of Medicine

Rush University Medical Centre

Chicago

Disclosures

KJP declares that she has no competing interests.

Acknowledgements

Dr Kyle J. Popovich would like to gratefully acknowledge Dr Dara Grennan, Dr Paul F. Roberts, and Dr R. John Presutti, the previous contributors to this topic.

Disclosures

DG, PFR, and RJP declare that they have no competing interests.

Peer reviewers

Chad M. Hivnor, Major, USAF, MC, FS

Chief

Outpatient & Pediatric Dermatology

59th Medical Wing/ SGOMD

Lackland Air Force Base

San Antonio

Disclosures

CMH declares that he has no competing interests.

Linda Kalilani, MBBS, MPhil, PhD

Epidemiologist

College of Medicine

University of Malawi

Zomba

Malawi

Disclosures

LK declares that she has no competing interests.

Christine Radojicic, MD

Professor

Cleveland Clinic Foundation

Cleveland

Disclosures

CR declares that she has no competing interests.

Alistair Leanord, BSc, MBChB, MD, DTM&H, FRCPath

Consultant Microbiologist

Microbiology Department

Southern General Hospital

Glasgow

Disclosures

AL declares that he has no competing interests.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

Gorwitz RJ. A review of community-associated methicillin-resistant Staphylococcus aureus skin and soft tissue infections. Pediatr Infect Dis J. 2008 Jan;27(1):1-7. Abstract

Nathwani D, Morgan M, Masterton RG, et al. Guidelines for UK practice for the diagnosis and management of methicillin-resistant Staphylococcus aureus (MRSA) infections presenting in the community. J Antimicrob Chemother. 2008 May;61(5):976-94.Full text Abstract

Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis. 2014 Jul 15;59(2):e10-52.Full text Abstract

Brown NM, Goodman AL, Horner C, et al. Treatment of methicillin-resistant Staphylococcus aureus (MRSA): updated guidelines from the UK. JAC Antimicrob Resist. 2021 Mar;3(1):dlaa114.Full text Abstract

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials
- Insect or spider bite
- Cellulitis
- Folliculitis
More Differentials
Guidelines
- Practice recommendation: strategies to prevent methicillin-resistant Staphylococcus aureus transmission and infection in acute-care hospitals: 2022 update
- Strategies to prevent surgical site infections in acute-care hospitals: 2022 update
More Guidelines
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Methicillin-resistant Staphylococcus aureus (MRSA)

Summary

Definition

History and exam

Key diagnostic factors

Other diagnostic factors

Risk factors

Diagnostic tests

1st tests to order

Tests to consider

Treatment algorithm

skin and soft-tissue infection: community-associated

skin and soft-tissue infection: healthcare-associated

bacteremia

pneumonia

visceral abscess

endocarditis

septic arthritis

urinary tract infection (UTI)

osteomyelitis

recurrent skin and soft-tissue MRSA infections in colonized patients

Contributors

Authors

Kyle J. Popovich, MD MS

Disclosures

Acknowledgements

Disclosures

Peer reviewers

Chad M. Hivnor, Major, USAF, MC, FS

Disclosures

Linda Kalilani, MBBS, MPhil, PhD

Disclosures

Christine Radojicic, MD

Disclosures

Alistair Leanord, BSc, MBChB, MD, DTM&H, FRCPath

Disclosures

References

Key articles

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials

Guidelines

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

Log in to access all of BMJ Best Practice