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Infection Control 2 – Community-Acquired MRSA
Staphylococcus aureus is a bacterium that commonly inhabits the skin and nose of
healthy individuals. In hospitals, it can act as an opportunistic pathogen, infecting
patients through surgical wounds, burns, sores, and other breaks in the skin to cause
diseases ranging from minor skin irritations to pneumonia and toxic shock
syndrome[1,2].
The first Methicillin-Resistant S. aureus (MRSA) isolates were identified in 1961[3].
Today, MRSA accounts for approximately 40% of clinical S. aureus isolates in the
UK[4], with a varying prevalence in other countries.
Question 1: What is Community-Acquired MRSA and what infection control
challenges does it pose?
Community-Acquired MRSA (CA-MRSA) infections may be caused by strains with a
true community origin, or by Healthcare-Associated MRSA (HA-MRSA) strains that
have been released into the community[1]. A thorough examination of cases often
reveals risk factors for HA-MRSA infection[5], suggesting that many cases are
attributable to community-onset HA-MRSA.
‘True’ CA-MRSA strains, however, can cause severe infections in young – otherwise
healthy – people in the absence of these risk factors. These strains differ from HAMRSA in their transmissibility, toxicity, and response to antibiotics. Naimi et al.[6]
and others have demonstrated both clonal spread in the community, and that
community MRSA isolates are genetically distinct to known nosocomial strains.
Thus, the HPA recommends that HA- and CA-MRSA be classified by genotype[9].
CA-MRSA strains possess more toxin genes than HA-MRSA strains, and express
them at higher levels. Toxins found in CA-MRSA strains include Panton-Valentine
Leukocidin (PVL), which is responsible for necrotising pneumonia, and superantigens
such as SEB and SEC, which cause toxic shock[7].
As with HA-MRSA strains, resistance to methicillin and other beta-lactams is
conferred by two genes: the blaZ gene, which encodes a beta-lactamase; and mecA,
which encodes an altered Penicillin-Binding Protein, PBP2a, allowing peptidoglycan
synthesis to proceed in the presence of methicillin and other beta-lactam antibiotics.
The mecA gene is carried on a mobile genetic element, SCCmec[1].
Oliveira and de Lencastre[8] used multiplex PCR to distinguish four SCCmec
elements. Types II and III contain multiple resistance determinants in addition to
mecA and are found in multi-drug resistant HA-MRSA. Type IV contains mecA as
the sole resistance determinant. CA-MRSA strains usually contain the type IV
element, and are thus susceptible to most commonly-used antibiotics except betalactams.
There have been no systematic studies to determine to prevalence of CA-MRSA in
the UK, but the HPA identified only 100 isolates between 2002 and 2005, and
considers the level of MRSA colonisation in the community to be low[9].
However, worldwide, there have been a number of CA-MRSA outbreaks over the past
two decades, both in community[10,11] and hospital[10,12.13] settings. There is concern
that such outbreaks will become more common and will move increasingly into the
healthcare environment, where CA-MRSA will be easily transmitted because of the
high concentration of people in these facilities, and its ability to infect both well and
unwell people[14]. There is also concern that exposure to nosocomial antibiotic
pressure could encourage multiple resistance in CA-MRSA[14].
Three of 4 UK CA-MRSA lineages carry the PVL gene[9], and the first PVL-positive
CA-MRSA outbreak in a UK hospital occurred in late 2006[15]. Out of 8 colonised
people, four developed infections, two of whom died.
Question 2: Compare and contrast the control of CA-MRSA with that of HAMRSA. Are the guidelines adequate?
In both hospitals and community healthcare facilities, there should be designated
individuals responsible for patient transfers, antibiotic stewardship, and infection
control. These should have such authority that any measures can be effectively
implemented. Depending on the size and nature of the establishment, community care
facilities may have their own infection control nurse or may use the infection control
services of a local hospital.
Because most MRSA infections occur in hospitals, and because these infections are
more likely to result in severe disease, infection control practices must be more
comprehensive in these institutions. However, the basic principles of infection control
are applicable to both community and hospital settings.
Basic infection control principles:
In both settings, hand-washing is thought to be the single most important factor
governing successful control of MRSA transmission. Both community[16] and
hospital[17] guidelines recommend the proper use of disposable gloves and aprons, but
stress that these do not negate the need for hand-washing. Healthcare workers must
wash their hands before and after treating a patient or performing an aseptic
procedure, after coming into contact with organic waste and contaminated items, and
after removing gloves. In hospitals, alcohol gels are used to wash hands. These are as
effective as soap and water against MRSA, but eliminate the need to dry hands, thus
increasing compliance. Also, in both settings, patients and visitors must be informed
of the importance of good hand hygiene in combating MRSA.
Both hospital and community guidelines stress the need for skin lesions to be covered
with an impermeable dressing, and for treatment of any responsible skin condition.
Staff with lesions must have them dressed and treated, and should seek occupational
health guidance from their GP.
MRSA has been shown to survive in dust and on equipment for long periods, and both
hospital and community guidelines propose that enhanced environmental cleaning and
increased adoption of single-use items are important measures in the control of
MRSA and other infectious diseases. In both hospitals and community care facilities,
regular audits should be performed to maintain cleanliness.
Additional controls in hospitals:
In hospitals, all high risk patients should be screened upon admission, unless they are
being admitted directly to isolation facilities. High risk patients should also be subject
to further periodic sampling. High-risk patients include:
 Those with history of MRSA carriage
 Those in frequent contact with the healthcare environment
 Those transferred from a hospital or community care facility believed to have
a high MRSA prevalence
 Those with eczema, dermatitis or psoriasis
In times of high MRSA incidence, in the hospital or the community, the infection
control team may wish to temporarily screen all patients. Discharge screening is not
recommended except for epidemiological purposes, as colonisation is not grounds for
continued hospitalisation. All hospitals must report their MRSA and MSSA figures to
the HPA as part of the Department of Health’s mandatory surveillance programme.
In hospitals, movement of MRSA-colonised patients between wards should be
avoided, as long as this doesn’t interfere with the patient’s wellbeing. Infected
patients may be considered for isolation by the infection control team if facilities
permit this, and if the patient is considered a “heavy shedder” (e.g. burns patients,
eczema sufferers, etc) or is believed to carry a particularly toxigenic, resistant, or
transmissible strain. Otherwise, they may be considered for cohorting.
In contrast, guidelines for community care facilities and patients’ own homes
encourage normal movement of colonised patients, stressing that a patient’s MRSA
status should not exclude them from social activities, as long as skin lesions are
properly covered and basic hygiene is performed.
Decolonisation of the skin, nose, and throat is often performed in hospitals before
elective surgery. This reduces the risk of a surgical wound becoming infected. It is
stressed that it is not always possible to completely eradicate MRSA, and additional
decolonisation courses are unnecessary after discharge into the community.
Revised guidelines:
The revised guidelines for prophylaxis and treatment of MRSA infections are directly
applicable to both community and hospital settings[18], while those for lab diagnosis
and susceptibility testing[19] and control and prevention of MRSA in hospitals[17] are
not, although the latter may be adopted to some extent by community care facilities.
In 2006, the UK government unveiled proposals to move patient care increasingly
into the community, with GPs and community hospitals to perform minor surgery and
other outpatient procedures[20]. However, in some parts of the world, MRSA accounts
for a rapidly increasing proportion of all community S. aureus isolates[21].
Thus, it can be seen that patients in the community will be put increasingly at risk of
MRSA infection. Therefore, new guidelines for the control of MRSA in the
community are needed to replace the 1995[16] guidelines, and should be more
expansive, with an increased emphasis on the screening and decolonisation of
patients.
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