MRSA Screening

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.

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.

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.

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.

Yes, being successfully treated for MRSA colonisation does not prevent you from getting it again.