To detect MRSA (Meticillin resistant staphylococcus aureus) carrier status
When your doctor wants to determine if you are a MRSA carrier (bacteria are present on the skin and maybe multiplying but you have no evidence of an active infection) or to determine if you have an active MRSA infection (bacteria invades the skin or deeper tissues and multiplies) or to determine if MRSA are still present after an infection has been treated with appropriate antibiotic therapy.
MRSA screening may also be requested before hospital elective surgery procedures or during emergency hospital admissions.
This test detects the presence of Meticillin Resistant Staphylococcus aureus (MRSA) and sometimes evaluates the genetic characteristics of the strain.
MRSA are strains of Staphylococcus aureus, or “staph,” bacteria that have become resistant to some of the antibiotics commonly used to treat these type of infections, (the betalactum group of antibiotics) which include the penicillins, meticillin and cephalosporins. Standard courses of antibiotics may be adequate to treat regular “staph” infections but often lead to treatment failure in patients with MRSA. Stains of MRSA were first identified in the early 1960’s and MRSA outbreaks have been a problem in confined populations such as hospitals, prisons, and nursing homes ever since. MRSA strains have caused a significant number of severe skin, lung, bone, and heart-related infections that have proven difficult to treat and in some cases proven fatal. All hospitals have implemented measures in an attempt to eradicate MRSA and to control the spread of MRSA from person to person. This has been a challenge as “staph” is a common bacterium that colonises the skin and in the nose of about 20-40% of the population. In the past, only about 0.8 % of the colonising “staph” were MRSA, but in the last decade this has risen above 1%, and studies of select populations have shown MRSA colonisation rates as high as 22% in care home residents.
There have been outbreaks of MRSA outside the hospital setting and in the last few years the number of cases have greatly increased. Therefore raising concern among doctors and other healthcare workers. In the community, MRSA is causing infections in young previously healthy people with no apparent risk factors of infection. Studies of these cases have shown that the bacteria are being spread in the community by MRSA colonised or infected people through close contact (such as sports or a day care) and through contact with contaminated objects (such as sports equipment, shared towels or razors) Often the infection it causes will be a long-lasting skin or lung infection.
Studies have also shown that the community acquired strains of MRSA were frequently genetically different from those found in the hospital setting (indicating that they developed separately). They were resistant to antibiotics routinely prescribed to treat skin infections and in some cases have proven to be especially harmful, producing toxins and causing an invasive infection. These strains of MRSA are now being found in hospitals as well, with infected and/or colonised patients and healthcare workers bringing them into this setting.
How is the sample collected for testing?
A nasal swab is collected by rotating a swab inside of each nostril. Occasionally a swab of a wound infection site or from a skin lesion are collected.
How is it used?
A 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 colonised patient or to detect if these resistant bacteria remain at a wound site after the patient has been treated for a MRSA infection. On a community level, screening may be used to help determine the source of an outbreak and on a national level used to evaluate the genetic characteristics of an identified MRSA strain.
The most widely used test to identify MRSA colonisation is culture. This test is definitive but usually takes 1 to 2 days for the result. The collected swab (nasal, wound swab or skin lesion swab) is cultured by putting into a special nutrient broth, or spread onto a nutrient gel plate. This is then incubated and examined for the growth of characteristic MRSA colonies.
Hospitals have now put in place measures to control the spread of MRSA by screening those patients they feel are at risk of being a carrier (everyone or specific target groups). Healthcare workers and the family members of carriers may also be screened for MRSA. When an outbreak of MRSA occurs in the community numerous MRSA screens may be performed to help identify the source of the infection. In some settings, such as nursing homes a large number of people may be screened to evaluate the spread of colonisation in a specific population.
Faster methods of MRSA screening by molecular methods have been developed to identify possible MRSA carriers. These new methods test for certain genetic components of MRSA, such as the mecA gene. The mecA gene confers resistance to the antibiotics meticillin, and flucloxacillin. While testing for mecA is not yet widely used, it does have the potential to detect nasal or wound carriage within hours instead of days required by culture. Research is underway to determine the utility of the rapid and more expensive molecular test.
When is it requested?
MRSA screening tests may be requested when a doctor, hospital, or researcher wants to evaluate potential MRSA colonisation in an individual, their family members or a group of people in the community as the source of a MRSA infection. Specific populations that have close contact such as 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. MRSA screening may also be requested on a person who has been treated for an MRSA infection or for MRSA colonisation to determine whether MRSA is still present on the skin or wound site. MRSA screening is also carried out before hospital elective surgery admissions and on emergency hospital admissions. Screening identifies colonised or infected individuals who can then be managed and to reduce the spread of MRSA to others.
What does the test result mean?
If a screen is positive for MRSA, then the patient is a carrier. If a wound site swab of a person treated for MRSA is still positive, then the bacteria are still present. If the nasal screen or wound site swab is negative, then MRSA is either not present or is present in very low numbers. If a molecular test confirms the presence of mecA in S. aureus then the organism is classified as MRSA.
Is there anything else I should know?
A sampling of positive MRSA tests may be subjected to further testing to help investigate the spread of MRSA within a community or region but are not often used in the treatment of an individual patient. These include pulsed-field gel electrophoresis (PFGE) which can identify the type and subtype of S. aureus strains and DNA testing, which can be used to look at the genetic material of the bacteria and detect the presence or absence of the mecA gene, which confers resistance to methicillin, and flucloxacillin antibiotics.
In a research setting, DNA testing is also being performed to detect the presence of the Panton-Valentine leukocidin (PVL) gene. This gene is associated with the production of a toxin that can greatly increase the complications associated with MRSA infections and can occasionally prove fatal.
Public awareness of MRSA and measures to control its spread are growing. With the importance of good hand hygiene before and after direct patient contact or patients surroundings (bed, table or equipment). Doctors are being encouraged to request MRSA screening on their patients with skin infections, in cases where they suspect a MRSA carrier and prior to hospital admission or elective surgery. Standard courses of antibiotics may be adequate to treat regular “staph” infections but often lead to treatment failure in patients with MRSA. Suppression of MRSA carriage can be treated by the use of 2% mupirocin nasal cream and 4% chlorohexidine gluconate shampoo/body wash.
Can I get MRSA more than once?
Can I be colonised with MRSA and not know it?
Are different strains of MRSA always identified?
No, not routinely. In the community and research setting strains may be identified to evaluate their genetic characteristics, to track outbreaks and to monitor their geographical spread.
On This Site
Tests: Wound Culture
Conditions: Staph Wound Infections and Meticillin Resistant Staphylococcus aureus