Over the past few years an increasing
number of reports from the US have suggested that a
new community-associated strain of Staphylococcus
aureus with resistance to methicillin (CA-MRSA)
has replaced conventional methicillin susceptible S
aureus as a significant pathogen in healthy community
dwelling individuals. A recent report demonstrated that
MRSA was the most common identifiable cause of skin
and soft tissue infections amongst patients presenting
to emergency departments in 11 American cities. Similar
reports have also emerged in Canada.
What is this new pathogen and what
does it mean for us? This pathogen is unique in that
it is not merely a hospital associated MRSA which is
now found in the community. This pathogen has a completely
different antimicrobial susceptibility profile. In addition,
the CA-MRSA variant has been seen to affect persons
who may live in crowded environments with suboptimal
hygiene. It's also been noted to harbour the Panton-Valentine
leukocidin (PVL) toxin which is lethal for neutrophils
and speculated to be the key factor responsible for
the cutaneous abscesses and necrotizing pneumonias.
This virulence factor is not traditionally observed
in the healthcare associated MRSA strains.
In reviewing epidemiological trends
over the past few years, it looks like CA-MRSA is with
us to stay. It's impossible to effectively predict which
patient will become infected, though one can speculate
based on high risk groups. It's harder to know which
antimicrobial therapy should be initiated, when and
how. To address some of these questions "Guidelines
for the Prevention and Management of Community Associated
Methicillin Resistant Staphylococcus aureus (CA-MRSA):
A Perspective for Canadian Healthcare Practitioners"
has been drafted (see "Are
you ready for the superbug?"). This report provides
a practical approach to the diagnosis and management
of infections caused by CA-MRSA. Thankfully, this pathogen
is susceptible to agents such as trimethoprim sulfamethoxazole
(TMP/SMX), doxycycline, clindamycin and the quinolones.
Clearly the diagnosis and therapy
for CA-MRSA related infections currently falls in that
gray area that is between the art and science of medicine
since clinical acumen is required to establish the diagnosis
and initiate an empiric treatment as CA-MRSA in Canada
has not replaced conventional strains of S aureus.
Until that time, however, we will continue to contemplate
how best to diagnose this pathogen. The new Canadian
recommendations are certainly of great benefit in helping
guide diagnosis, treatment and in some cases, potentially
decolonization. — Dr John M Embil, MD, FRCPC,
Associate Professor, University of Manitoba and Medical
Director, Infection Prevention and Control Program,
Health Sciences Centre and Winnipeg Regional Health
Authority.
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