An MRSA screen is a test that looks solely for the presence of MRSA and no other . It is primarily used to identify someone who may be with MRSA. Reasons for screening include determining whether extra precautions are required to ensure the bacteria are not spread, or occasionally to identify the source of an outbreak.
The most widely used test to identify MRSA colonisation is . This confirms the presence of MRSA and allows the organisms to be further characterised, however culture often takes one to two days to yield a result.
The material from the swab is put onto a special then incubated in an environment that encourages the bacteria to grow. It is then examined for MRSA colonies.
Some hospitals have instituted measures to control the spread of MRSA by screening patients they feel are at risk, other hospitals screen all new admissions. When an outbreak of MRSA is under investigation, screening of health care workers, family members and close contacts may be performed to identify the potential source of infection and to help devise a plan of containment. In some settings, such as nursing homes, a large number of people may be screened.
Faster methods of MRSA screening by molecular methods have been developed. These new methods test for the mecA gene that confers resistance to the ß-lactam antibiotics. Molecular tests for MRSA screening have the potential to provide results within hours instead of the days required by culture and are being used more commonly.
A MRSA screening test may be ordered when a doctor, hospital, community health department, or researcher wants to evaluate potential MRSA in an individual, their family members, and/or a group of people in the community as the source of a MRSA infection. A person who has been treated for MRSA infection or for MRSA colonisation will often be screened several times to determine whether MRSA is still present or whether the person has "cleared" their carriage.
If MRSA is detected from a screening swab, the person is colonised with MRSA. Failure to detect MRSA from a screening swab means that MRSA is either not present or is present in numbers too low to be detected by the test. If this is following treatment or eradication of MRSA in someone, several swabs will be collected over time and the repeated failure to detect MRSA will tell the healthcare team that this person has cleared their carriage of MRSA.
Further testing may be performed on MRSA bacteria when they are isolated in a . These additional research tests can identify the type and subtype of S. aureus strains. Although the typing may not be used to determine treatment of the patient, it provides information to track the pattern of disease spread of the infection and characterise the toxins and other virulence factors present in the bacteria.