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This page was updated on September 27, 2005 to incorporate the corrections
in Vol. 11, No. 11
Letter
Methicillin-resistant Staphylococcus
aureus Necrotizing Pneumonia
Monica Monaco,* Rosa Antonucci,† Paolo Palange,† Mario Venditti,†
and Annalisa Pantosti*
*Istituto Superiore di Sanità, Rome, Italy; and †Università La Sapienza,
Rome, Italy
Suggested
citation for this article
To the Editor: Methicillin-resistant Staphylococcus aureus
(MRSA) strains account for >40% of all hospital-acquired S. aureus
infections in Italy (1). Although cases of community-acquired
MRSA (CA-MRSA) infections have been reported in recent years (2),
these isolates have not been characterized for Panton-Valentine leukocidin
(PVL) (3); therefore, the presence of isolates with the
typical characteristics of CA-MRSA (4) in Italy remains
unknown.
At the beginning of April 2005, a 37-year-old woman was admitted to the
University Hospital Policlinico in Rome because of fever, cough, and headache.
Her medical history was unremarkable. She was a teacher in a school for
foreign students in Rome, smoked 3 cigarettes per day for 15 years, and
reported no recent travel abroad. Her 5-year-old daughter had influenzalike
symptoms in the previous week. At hospital admission, her temperature
was 39°C, heart rate was108 beats/min, respiratory rate was 32 breaths/min,
and blood pressure was 105/70 mmHg. Arterial blood gas analysis showed
mild hypoxemia and hypocapnia (PaO2 73 mm Hg and PaCO2
34 mm Hg on room air). Leukocyte count was 24,360 cells/μL (81% polymorphonuclear
cells), and platelet count was 506,000/μL. Chest radiograph showed
infiltrates in the right upper and lower lobes and left lower lobe. Empiric
treatment with clarithromycin and ceftriaxone was started, but the patient's
clinical conditions did not improve. Culture of sputum samples obtained
at admission yielded growth of MRSA. Computed tomographic scan showed
multiple lung cavitary lesions, indicating necrotizing pneumonia. On day
3 of admission, antimicrobial drug therapy was changed to linezolid (600
mg 2 times a day). Fever resolved, and the patient's condition rapidly
improved. The patient was discharged after 14 days of linezolid treatment.
At discharge, leukocyte count was 6,040 cell/μL (58% polymorphonuclear
cells), and arterial blood gas analysis showed PaO2 of 88 mm
Hg.
The MRSA isolate from sputum was susceptible to all the non–β-lactam
antimicrobial drugs tested, including erythromycin, clindamycin, ciprofloxacin,
tetracycline, kanamycin, and fusidic acid. With established molecular
methods, the isolate was found to harbor SCCmec type IV (5);
lukS and lukF, the genes coding for the 2 subunits of the
PVL toxin; and hlg, the γ-hemolysin gene (3).
The genetic background of the isolate was determined by multilocus sequence
typing (MLST) (6) and sequence typing of the tandem repeat
region of protein A gene (spa typing) (7). Results
showed that the isolate belonged to ST30 according to the MLST database
(http://saureus.mlst.net), and
spa typing, analyzed by the Ridom Staphtype software (http://www.ridom.de),
indicated a novel spa type, to which type 755 was assigned. ST30,
1 of 6 clones more commonly associated with PVL-positive CA-MRSA (4),
is designated also the southwest Pacific (SWP) clone, because of the area
in which it circulates. Recently, the SWP clone has caused CA-MRSA infections
in northern European countries (England, Scotland, the Netherlands, Sweden,
and Latvia) (8,9). Molecular analysis suggests that the
SWP clone has evolved from a methicillin-susceptible clone of S. aureus,
termed phage type 80/81, that was pandemic in the 1950s and considered
to be unusually virulent and transmissible (8). In fact,
strains belonging to phage type 80/81 carry the PVL gene and appear to
have subsequently acquired methicillin resistance through horizontal transfer
of SCCmec type IV. The spa type of the Italian isolate comprises
7 nucleotide repeats, indicated by XJ4AKAOM in the alphabetical code.
This repeat sequence differs from that of the classical SWP clone, indicated
by XKAKAOMQ (8), by only 1 bp in the second repeat and
loss of the last Q repeat. In spite of these differences, the spa
type is in substantial agreement with the MLST result and indicates that
the Italian isolate is either a descendent or a local variant of the SWP
clone. The most common clone of CA-MRSA described in Europe is ST80, spa
type 44. CA-MRSA belonging to ST80 tend to be more antimicrobial drug
resistant than isolates belonging to other clones (4).
Resistance to fusidic acid, typical of ST80, has been proposed as a marker
for CA-MRSA in Europe (10). In light of our finding,
we cannot rely on resistance to fusidic acid to screen for PVL-producing
CA-MRSA in our country.
To our knowledge, this is the first report from Italy of necrotizing
pneumonia caused by PVL-positive CA-MRSA. The presentation was typically
that of a severe pneumonia that occurred in a previously healthy, young
adult with no risk factors for MRSA acquisition, as described in other
cases (11). This is also the first report of a SWP clone
isolate in southern Europe; if the strain is circulating in Italy or is
occasionally imported from the SWP area, whether our patient acquired
it through contact with a foreign contact remains unknown.
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Suggested citation
for this article:
Monaco M, Antonucci
R, Palange P, Venditti M, Pantosti A. Methicillin-resistant Staphylococcus
aureus necrotizing pneumonia [letter]. Emerg Infect Dis [serial on
the Internet]. 2005 Oct [date cited]. Available from http://www.cdc.gov/ncidod/EID/vol11no10/05-0776.htm
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