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.
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. 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. 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
Other diagnostic factors
- infection unresponsive to penicillins
- history of a presumed spider bite
- abscess formation
- 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
- 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)
1st investigations to order
- blood culture
- urine culture
- tissue culture
- sputum culture
- arthrocentesis fluid culture
- indwelling vascular catheter tip culture
Investigations to consider
- polymerase chain reaction (PCR)
skin and soft-tissue infection: community-associated
skin and soft-tissue infection: healthcare-associated
urinary tract infection (UTI)
recurrent skin and soft-tissue MRSA infections in colonized patients
- Insect or spider bite
- 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
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