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. On a community level, screening may be used to help determine the source of an outbreak. On a national level, additional testing may inform clinicians and researchers about the unique genetic characteristics of the strains of MRSA circulating in the community or health care setting.
MRSA colonization may be determined by a bacterialculture or a molecular test that detects the DNA and resistance gene of MRSA. A nasal swab is collected from the nares (nostrils) of an asymptomatic person and cultured (put onto a special nutrient medium, incubated, and then examined for the growth of characteristic MRSA colonies). A swab may be collected from a wound site or skin lesion of a person who has been previously treated for a MRSA infection and cultured similarly. A screening culture identifies the absence or presence of MRSA and usually takes 1 to 2 days for a result.
Molecular tests for MRSA screening have the potential to detect nasal or wound carriage within hours, allowing for prompt treatment as necessary. The same specimen types are used in a molecular test, but the specimen is analyzed for the genetic markers to identify S. aureus and the mecA gene that confers resistance to methicillin, oxacillin, nafcillin, dicloxacillin, and other similar antibiotics.
Some hospitals have instituted measures to control the spread of MRSA by screening those patients they feel are at risk of being colonized with these resistant bacteria (a carrier) or all new admissions to the hospital. When an outbreak of MRSA is under investigation, screening of health care workers, family members, and close contacts may be performed to identify the source of the infection and to help devise a plan to contain these infections. In some settings, such as nursing homes, a large number of people may be screened to evaluate the spread of colonization in a specific population.
A MRSA screening test may be ordered when a health care provider, hospital, or health department needs to evaluate potential MRSA colonization in an individual, their family members, and/or a group of people in the community as the source of a MRSA infection.
Specific populations that have close physical contact, such as a sports team, residents of a nursing home, or health care workers, may be tested for MRSA carrier status when an increased number of infections occur within their close group.
Occasionally, a person who has been treated for MRSA infection or for MRSA colonization may be screened to determine whether MRSA are still present.
Further testing may be performed on MRSA bacteria when they are isolated in a culture. 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 characterize the toxins and other virulence factors present in the bacteria.
A study comparing prevention strategies for bloodstream infections found that decolonizing intensive care unit (ICU) patients who are MRSA-positive based on screening tests was not as effective at reducing these infections as administering a course of a nasal antibiotic and cleansing patients with special antimicrobial wipes for all patients admitted to the ICU. As a result, hospital policies may change in the future and less MRSA screening may be performed in these settings.
This article was last reviewed on August 6, 2013. | This article was last modified on May 13, 2014.
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