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Bacterial Infections
Methicillin-resistant Staphylococcus aureus in Cystic Fibrosis
a report by
Giovanni Taccetti,
1
Silvia Campana,
1
Priscilla Cocchi,
1
Anna Silvia Neri,
1
Francesca Trevisan,
1
Vanessa Boni,
1
Cesare Braggion
1
and Filippo Festini
2
1. Cystic Fibrosis Centre, Meyer Hospital, Florence; 2. Department of Paediatrics, University of Florence
Cystic fibrosis (CF) is the most common inherited disease in the Caucasian MRSA can be resistant either just to methicillin and other beta-lactam
population and results from a defective chloride channel, the cystic antibiotics or also to other classes of antibiotics such as tetracyclines,
fibrosis transmembrane regulator (CFTR).
1
CF patients’ lungs become an trimethoprim–sulfamethoxazole, rifampin, clindamycin, quinolones and
ideal habitat for several bacterial species. Staphylococcus aureus is usually macrolides or even to multiple classes of antibiotics.
5
In this latter case, it
the first pathogen to colonise the airways of CF patients, and in the pre- should be called multidrug-resistant MRSA.
8
Most hospital-associated strains
antibiotic era this pathogen was the major cause of morbidity and are resistant to several classes of antibiotics, whereas most community-
mortality.
2,3
Recently, the importance of non-fermentative Gram-negative associated strains are susceptible to tetracyclines, trimethoprim–
species has been noted, but an additional matter of concern for CF sulfamethoxazole and clindamycin.
6,8,16,17
patients is represented by the emergence of methicillin-resistant S. aureus
(MRSA).
4–10
Since the first isolation of MRSA in the 1960s, this pathogen Epidemiology
has become an important cause of infection and one of the most MRSA is now recognised as a public health problem worldwide because
prevalent causes of nosocomial infections.
5–8
Its role in CF has not been of increasing rates of infection in many settings.
5,6,18
Studies analysing
well understood to date. There is little evidence available about its risk factors for acquiring MRSA in patients not affected by CF show that
prevalence, antibiotic resistance pattern, epidemiology, transmissibility, the risks of nasal carriage of healthcare-associated MRSA (HA-MRSA)
virulence and clinical impact on CF patients.
9–14
An improvement in our include hospitalisation, prolonged hospital stay, frequent contact with a
knowledge of this important emerging pathogen could be vital to the healthcare environment, recent (within the previous 60 days)
management of pulmonary infections in CF patients. This review focuses antimicrobial use or frequent contact with an individual with one or
on the epidemiology, microbiology, clinical significance and treatment of more of the preceding risk factors.
6,19
In non-CF environments,
MRSA in CF patients. infections caused by MRSA occur primarily in healthcare environments,
although recently there has been an increase in MRSA epidemics in rural
Nomenclature and urban areas that do not have any contact with healthcare
The terminology used for cases of colonisation or infection due to MRSA environments. These observations suggest that the epidemiology of
is varied. The Centers for Disease Control and Prevention (CDC) defines a MRSA infections is changing.
10,16
case of MRSA infection as community-acquired when it is diagnosed in
outpatients or within 48 hours of hospitalisation if the patient lacks the From a microbiological point of view, the community-associated MRSA (CA-
traditional risk factors for MRSA.
6,7
The CDC defines hospital-acquired MRSA) strains differ from HA-MRSA strains in that they are usually
MRSA infections as those in patients who have had frequent or recent susceptible to clindamycin and other non-beta-lactam antibiotics. However,
contact with hospitals or healthcare facilities within the previous year or the level of their resistance is increasing and geographically variable.
20
On a
who have recently undergone an invasive medical procedure.
15
The term genetic level, the type IV or V variants of the gene cassette codify for
‘healthcare-acquired MRSA’ is preferable because it includes the methicillin resistance (SCCmec). Furthermore, CA-MRSA strains ususally
possibility of acquiring an infection in an extrahospital environment, in carry the two genes encoding for the pore-forming toxin named Panton-
relation to the evolution of the organisation of care for CF patients.
8
The Valentine leukocidin (PVL). In non-CF environments, CA-MRSA strains
terms ‘associated’ or ‘acquired’ are often used interchangeably.
5,6
synthesise PVL (PVL+); are responsible for tissue necrosis; are cytolytic to
Recently, it was suggested that the term ‘associated’ be used to describe macrophages, monocytes and polymorphonuclear granulocytes; and have
strains isolated either in the community or in healthcare environments in been linked epidemiologically to cutaneous and more severe infections.
21,22
a context in which the strain acquired is not precisely identified. Instead, Recent studies have demonstrated that the CDC definition underestimates
the term ‘acquired’ is to be used to describe the location of MRSA the CA-MRSA prevalence because many patients previously exposed to the
exposure that led to colonisation or infection.
8
healthcare environment harbour strains of the multilocus sequence type
(MLST)
8
typical of CA-MRSA, with clindamycin susceptibility, SCCmec IV-
bearing and PVL+.
7,23
Giovanni Taccetti is a physician at the Regional Cystic
Fibrosis Centre at the Meyer Pediatric Hospital in Florence.
His major research interests are in the field of cystic In the US, CA-MRSA strains are described as being in continuous increase in
fibrosis microbiology. Dr Taccetti is actively involved in
nosocomial environments, with a tendency to progressively replace strains
teaching and research. During his career, he has also been
a member of the governing council of the Italian Society
considered to be responsible for hospital infections (HA-MRSA). In Europe,
of Cystic Fibrosis.
the prevalence of infections attributable to CA-MRSA seems to be lower
E:
g.taccetti@meyer.it
than in the US, but is continuously increasing.
4,24
Recent observations based
on molecular studies suggest that the association with a healthcare
90 © TOUCH BRIEFINGS 2008
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