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Complicated Skin and Skin Structure Infections Due to Methicillin-resistant Staphylococcus aureus
More importantly, MRSA is increasingly reported to cause colonization and
Figure 1: Algorithm for Treating Patients with Skin and Skin
infection through skin contact in locker rooms and gymnasiums, even among
healthy populations and children.
Among intravenous drug abusers,
Patient presents with SSSI
MRSA causes as many as 20% of SA infections. MRSA is not only difficult to
treat, but probably also has increased virulence. Based on antibiograms,
Educate about MRSA possibility
Check for: family members with
CA-MRSA may represent a hybrid between HA-MRSA that escaped from the
SSSI, risk factors, pets in household,
hospital environment and the once easily treatable community organisms.
underlying conditions (DM, HIV)
Culture: infection site, nose, blood
Most of the hybrid strains have also acquired the virulence factor PVL,
WBC/CRP/imaging (CT, MRI)
making their infections more aggressive and resulting in deep-tissue
Uncomplicated SSSI Complicated SSSI
infections following minor scrapes and cuts.
In the US, the epidemic of CA-MRSA is due to a CC8 strain designated
No surgery No surgery Surgery Surgery
ST8:USA300 that carries mec type IV, PVL, and enterotoxins Q and K.
No antibiotics Antibiotics No antibiotics Antibiotics
Other common community-associated strains of MRSA are ST8:USA500
and ST59:USA1000. In community outbreaks of MRSA, two clones Follow-up: clinical response?
predominate in the US: USA 300 and USA 400. CA-MRSA USA 300 is
Microbiology: if MRSA, treat according to sensitivity testing.
Open question: Eradiaction? Isolation? Testing of family
now the predominant cause of community-onset SA skin and skin
members and pets?
structure infections (SSSIs).
Little is known about these infections in the
CRP = C-reactive protein; CT = computed tomography; DM = diabetes mellitus; MRI = magnetic resonance imaging;
non-outbreak setting; however, almost three-quarters of the soft-
MRSA = methicillin-resistant Staphylococcus aureus; SSSI = skin and skin structure infection; WBC = white blood cell.
tissue infections in one study were caused by MRSA (predominantly
the USA 300 type). No MRSA USA 300 isolate was resistant to against MRSA; rifampicin, fosfomycin, and fusidic acid may also be
trimethoprim–sulfamethoxazole (TMPS) or vancomycin, while most were useful.
In a recent study from Boston, a significant increase in CA-
resistant to erythromycin in addition to β-lactams. MRSA was reported during the past 10 years.
Whereas SSSIs in the
initial period were treated with β-lactams, at the end of the study almost
In other regions, similar clones have emerged, such as EMRSA15 and 75% of patients received TMPS. If patients received an active agent
EMRSA16 in the UK. Both the EMRSA15 and 16 strains are resistant to against the causative organism, the relapse and failure rates were
erythromycin and quinolone antibiotics that can penetrate intracellularly. significantly lower. Another study compared MRSA and methicillin-
These strains may grow intracellularly in the presence of these commonly sensitive SA (MSSA) SSSIs, and it was concluded that MRSA was an
used antibiotics and, therefore, are able to spread, unlike previous strains independent risk factor for an increased failure rate. Therefore,
that have failed to persist.
However, antibiotic exposure alone cannot empirical use of agents active against CA-MRSA is warranted for
patients presenting with serious SSSIs. β-lactams can no longer be
considered first-choice agents for SSSIs, and increasing resistance to
Methicillin-resistant Staphylococcus macrolides, lincosamines, and quinolones must be expected.
aureus is increasingly reported to
From a practical point of view, if CA-MRSA SSSI is suspected, currently
cause colonization and infection TMPS may be the best antimicrobial choice. Cultures must be obtained and
through skin contact in locker rooms
therapy adapted to the individual findings. Glycopeptides may be used
once the presence of MRSA has been confirmed, and glycopeptides should
and gymnasiums, even among healthy be used if outpatient HA-MRSA is to be considered. Recent exposure to
populations and children.
antibiotics, patients with known MRSA infection, and, most importantly,
recent hospitalization are indicators for possible TMPS resistance. Linezolid
has excellent activity against MRSA, perhaps even superior to that of
explain the recent increase in MRSA infections. Of note, MRSA USA 300 was vancomycin, and may assume a larger role in the management of MRSA
the strain initially isolated from intravenous drug abusers with SSSIs and in SSSIs in the future, particularly when oral agents are desirable.
HIV patients. These individuals frequently receive TMPS for prophylaxis is not licensed in the US; this agent allows once-daily dosing and may be
against Pneumocystis jiroveci pneumonia, and in one study TMPS did protect used in the outpatient setting. Daptomycin is a lipopeptide, which currently
against MRSA. On the other hand, exposure to β-lactams was a significant is reserved for vancomycin-resistant enterococcus (VRE) infections.
Since a recent history of syphilis was another risk factor, close Quinupristin/dalfopristin, daptomycin, and tigecycline should be reserved
contact to multiple sex partners was assumed to be another contributor. for the treatment of more severe infections that do not respond to other
Rapid detection of MRSA using polymerase chain reaction (PCR)
Antimicrobial Chemotherapy has been recently suggested in addition to new approaches.
MRSA may also be known as multiple-resistant SA. Whereas HA-MRSA
is commonly also resistant to macrolides, lincosamines, TMPS, New strains of MRSA have been found showing antibiotic resistance to
aminoglycosides, quinolones, and tetracyclines, CA-MRSA remains glycopeptides, such as vancomycin intermediate-resistant SA (VISA).
susceptible to some of these agents. Glycopeptides, oxazolidines, such, it is important that several new compounds with activity against
quinupristin/dalfopristin, and glycylcycline are agents specifically active MRSA, including β-lactams, are currently undergoing clinical trials.
US INFECTIOUS DISEASE 49
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