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Laboratory Tests

The purpose of laboratory testing is to identify the bacteria causing the wound infection and to determine the susceptibility of the microorganism to available antibiotics. If an infection is due to MRSA, it should be investigated to determine the source of the infection.

Testing for staph infections:

  • 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 cultureblood culture, a culture of joint fluid (synovial fluid) or even 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 in small numbers.
  • Susceptibility testing is performed if S. aureus are detected in a culture, to determine if the strain that is present is MRSA.

Rapid tests for the detection of MRSA have recently been developed. These tests are molecular-based or use immunoassay to determine if the drug-resistant bacteria are present. Whereas cultures typically take 24-48 hours, these tests provide results in 2-5 hours allowing for prompt action such as addition of different antibiotics and consideration of patient isolation in a hospital setting.

Identifying MRSA can sometimes be challenging. Most people have a mixed staph population. This means that even if someone has MRSA, not all of the staph present at the infection site will be equally resistant and  there is the potential for missing them.

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

Last Review Date: April 10, 2020