What is Methicillin Resistant Staphylococcus Aureus (MRSA, Staph Infection)?

Methicillin Resistant Staphylococcus Aureus (MRSA) refers to a disease caused by a bacteria known as Staphylococcus aureus. This bacteria commonly causes cellulitis and wound infections but it may also cause serious infections such as osteomyelitis (bone infection) or bacteraemia (infection of the bloodstream). The bacteria is normally present on the skin and in the nose of 30-50% of the general population, however it does not cause disease unless it effects a vulnerable site or person. MRSA refers to Staphylococcus aureus with an acquired resistance to methicillin (a powerful antibiotic) and commonly other antibiotic classes.
There are three main types of MRSA circulating around Australia currently:

  • Classical methicillin-resistant MRSA. This is also called Eastern Australia (EA) MRSA. It is generally resistant to beta-lactams, erythromycin, gentamicin and trimethoprim-sulfamethoxazole.
  • Community MRSA, which is also called Western Australia (WA) MRSA or Kimberley MRSA. This is generally resistant to methicillin and other beta-lactams, however it is generally sensitive to gentamicin.
  • Community MRSA different from WA MRSA, but it is similar to community strains in New Zealand and other South Pacific islands.

Statistics

MRSA is endemic (i.e. present at all times in a health care facility) in many major teaching hospitals in Australia. The true incidence of the bacteria is hard to ascertain however occasional episodic outbreaks occur around various parts of Australia. Most commonly it is EA MRSA which is present in hospitals. Community forms of MRSA are most prevalent in Western Australia.

Risk Factors

Infants and chronically ill patients are most at risk of acquiring MRSA. The elderly, debilitated, immunosuppressed and patients taking steroids in an acute care setting are particularly susceptible. Particular areas known to infect vulnerable patients include; intensive care facilities, renal units and surgical units. Patients with indwelling devices such as peripheral intravascular lines, central lines, urinary catheters, surgical drains, endotracheal tubes are also at higher risk.
In general risks for hospital patients of MRSA infection are compounded by:

  • length of hospital stay
  • nutritional status of the patient
  • severity of underlying disease
  • presence of indwelling devices
  • recent/longterm antibiotic treatment
  • presence of leg ulcers or wounds In general risks for community patients of MRSA infection are compounded by:
  • patients recently discharged from hospital
  • chronic leg ulcer patients
  • residents of long term stay health facilities (e.g. aged-care housing)
  • intravenous drug use
  • insulin dependent diabetics
  • patients with ongoing skin problems e.g. eczema.

It should be noted that the major source of transmission of MRSA in a hospital setting is via the hands of health care workers who may acquire the organism after touching a patient and may transmit by touching another patient without washing their hands.

Progression

MRSA colonisation usually precedes infection. This means that patients or healthcare workers usually acquire the bacteria on their skin or in their nasal carriage and may transmit it to other people. The bacteria may also be significant enought to cause disease in a person who is colonised, if they are particularly vulnerable. The extent of the disease caused by the bacteria is often dependent on how ill the patient is.

How is it Diagnosed

Blood Tests to determine if there is an infection may include:

  • Full blood count– a raised white cell count may be indicative of infection
  • ESR/CRP – these may be raised which is indicative of infection
  • Blood Cultures – may show MRSA if relevant Swabs may be taken from relevant infected sites which may isolate the bacteria.

Treatment

There is no real consensus on the standards of infection control for multiresistant organisms. The main factors that influence MRSA management in Australian hospitals are the endemicity of the organism in the health care establishment as well as the vulnerability of the patients. The use of additional precautions has been highly recommended in the management of MRSA. This includes:

  • Appropriate monitoring of the MRSA endemicity.
  • Identifying the causative organisms by culture.
  • Assigning patients to single rooms and bathroom facilities.
  • Healthcare staff using clean, non-sterile gowns and gloves when entering a patients room.
  • The gown and gloves should be carefully removed before leaving the room and hands should be washed with antiseptic handwash or alcohol based hand-rub.
  • A mask should be worn if there are colonised respiratory secretions.
  • Dedicated equipment should be allocated to the infected patient – this includes stethoscopes, thermometers etc. They should be cleaned and disinfected after each use. Disposable equipment is more desirable. Bedding and furniture should also be considered.
  • An infectious diseases physician and/or a clinical microbiologist should be involved in the care of MRSA positive patients. In terms of treating a patient who has a MRSA infection, antibiotics which may have some success include vancomycin and teicoplanin (glycopeptide antibiotics). Linezolid and quinupristin/dalfopristin are generally reserved for severe infections which do not respond to glycopeptides. All drugs are generally adminstered intravenously.