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Staph Infections and Methicillin-Resistant Staphylococcus aureus

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Laboratory Tests

MRSA Screening
A methicillin-resistant Staphylococcus aureus (MRSA) screen is a test that looks solely for the presence of MRSA and no other pathogens. It is primarily used to identify the presence of MRSA in a colonized person. Some hospitals have instituted screening to control the spread of MRSA. All patients may be screened on admission to the hospital or patients at high risk of being colonized may be screened (potential carriers).

See the section on Prevention and Treatment to learn more.

Diagnosis of Staph Infections
Laboratory testing is used to identify the bacteria causing an infection and to determine its susceptibility to antibiotics.

  • The primary test for diagnosis of a staph infection is a culture of the affected area. This may involve a bacterial wound culture using fluid or pus from a wound, a sputum culture, a blood culture, a culture of joint fluid (synovial fluid), or culture of breast milk (in the case of an infected breast). Sometimes, multiple samples are collected to evaluate different body sites or to attempt to detect bacteria that may be present.
  • Susceptibility testing is performed if S. aureus are detected in a culture, to determine if the strain that is present is MRSA and to determine which antibiotics are likely to be effective in treating the infection.
  • Rapid tests for the detection of MRSA are available. These tests detect the mecA gene or the gene's protein, which is PBP2a (penicillin-binding protein 2a). This is the gene or protein that confers methicillin resistance. Whereas cultures typically take 24-48 hours, these tests provide results in 2-5 hours, allowing for prompt treatment.

A variety of methods may be used to track different strains of MRSA. These are used in the investigation of the spread of MRSA within a community or region but are not used in the treatment of an individual person.

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