Dr. Mona, Chiu Lai Shan, 趙麗珊
Specialist in Dermatology and Venereology
S. aureus skin infection
Epidemiology and clinical characteristics of
Approach to CA-MRSA skin infection
Colonize the anterior nares in one third of
healthy population
Colonize the skin of most atopic dermatitis
patients (up to 100% in those with severe AD)
Common pathogen for skin infection
Notorious for secretion of various toxins and
superantigens (TSST, enterotoxin) which can
cause serious infection and promote
 Cellulitis
 Abscess
 Carbuncle
 Furuncle
 Impetigo
 Necrotizing fasciitis
 Staphylococcus scalded skin syndrome
 Toxic shock syndrome
-local prevalence
-travel history
 Clinical features
 Laboratory
-antibiotic resistance profile
1981-CA-MRSA outbreak was first described
in United States in a group of intravenous
drug users
1990s-multiple CA-MRSA outbreaks were
documented among different states in the
United States
1999-identify as a virulent pathogen after it
was identified as the causative organism in
the death of four previously healthy children
in Minnesota and North Dakota
2004-CA-MRSA was referred as “ an
emerging epidemic”
PR Cohen. International Journal of
Dermatology 2007. 46:i-11
Methicillin resistance is mediated by the
methicllin resistance gene: mecA gene
The gene is responsible for beta-lactam
resistance by encoding the methicillinresistant penicillin binding protein 2a (PBP2a)
which has a low affinity for beta-lactam type
The genetic elements that carries the mecA
gene is the staphylococcal cassette
chromosome (SCC)
HA-MRSA infection is associated with SCCmec
type I, II, III
CA-MRSA infection is associated with SCCmec
type IV and V which lacks other multidrug
resistance genes
CA-MRSA is more frequently associated with
exotoxins than the HA-MRSA counterpart
Panton-Valentine leukocidin (PVL) toxin is the
most common toxin
It is lethal to neutophils and is a potent
dermonecrotic toxin. It is also associated with
necrotizing pneumonitis
Patient population
Acquired after staying more
then 48 hours in the hospital
Community without exposure
to the hospital environment
Pre-disposing factors
Surgery, intubation, catheter,
dialysis, prior MRSA infection,
long term care facility
Members of military, IVDU,
homosexual males, children,
athletes, inmates,
Pregnant women, chidren and
Virulent factors
SCCmec type I to III
SCCmec type IV or V, PantonValentine leukocidin
Clinical presentations
Systemic infection such as UTI
and pneumonia
Most common soft tissue and
skin infection
Antibiotic resistance profile
Resistant to most antibiotics
except few (e.g.vancomycin,
Resistant to beta-lactam group
of antibiotic but susceptible to
quinolones and trimethoprim.
Topical fusidic acid and
mupirocin. Some are
susceptible to clindamycin
Large population based survey in the United
States showed a 0.84% of overall MRSA
colonization rate versus 31.6% of MSSA
Worldwide, the overall MRSA colonization rate
range from 0.26% to 9.2%
The overall prevalence of MRSA is around
1.4% in our locale and most of them are
associated with health-care exposure
The prevalence is similar in the United
Kingdom (1.5%) and <1% in Italy, Portugal
and Canada
The rate of MRSA colonization is higher in
healthy school children in Asian countries:
5.1% in South Korea, 4.3% in Japan, and 1.9%
in Taiwan
There were significant differences in the
prevalence of MRSA among distinct regions of
China, with the highest prevalence, 76.9%, in
east China, 52.3% in the southwest and about
60% in other regions
The prevalence of MRSA in certain cities such
as Shanghai, Beijing, and Guangzhou was
high relative to other
32.7% of S. aureus isolated from pediatric
patients was MRSA, which was about half that
seen in adult patient
The incidence of CA-MRSA in children with
skin and soft tissue infections was 1.1–4% in
Similar in other major provinces
MRSA among patients presenting to the
emergency department with purulent SSTI
were studied over a 4-month period from
November 2006 to February 2007.
It involved the emergency departments in six
regional hospitals estimated to provide
service to half of the 6.6-million inhabitants
in Hong Kong
Wound swabs were obtained for culture from
all patients who present with purulent SSTIs
of less than 7 days duration
A total of 298 patients aged 2 to 97 with
purulent SSTIs were recruited
S. aureus was isolated from 126 (42%)
Among patients with purulent SSTIs, 10%
(13/125) of all S aureus isolates was
attributed to PVL-positive communityassociated MRSA
MRSA was isolated from 5% (13/241) of
abscesses, 13% (5/40) of infected wounds,
and 17% (1/6) of purulent discharges
associated with cellulitis
In univariate analysis, Filipino ethnicity was
significantly more likely than Chinese to be
infected by PVL-positive communityassociated
All other clinical and epidemiologic features
were not predictive of PVL- positive
community-associated MRSA
Most common complain “spider bite” lesions
 Papules
 Pustules
 Erythematous or crusted erosions
 Plaques
 Nodules
 Legs
 Knees
 Thighs
 Feet
 Buttock
Severe infection:
 Necrotizing fasciitis
 Bullous erysipelas
 Staphylococcus scalded skin syndrome and
staphylococcus toxic shock syndrome
 Purpura fulminans
 Ecthyma gangrenosum
All are resistance to Beta-lactam group of
Most are susceptible to ciprofloxacin,
rifampacin, cotrimoxazoles, vancomycin,
mupirocin and fusidic acid
Most are resistance to erythromycin
Some are resistance to Clindamycin
Resistance to older generation of
fluoroquinolones is observed
Resistance rates of 57.1–85.7% to macrolides,
clindamycin, aminoglycosides,
sulfamethoxazole-trimethroprim, quinolones,
and tetracycline
Resistance rate to rifampicin was 28.6%
Y.-H. Xiao et al. Drug Resistance Updates 14 (2011) 236–250
Antibiotic susceptibilities of community-acquiredStaphylococcus aureus isolates recovered
from children at Texas Children's Hospital from 1 August 2001 through 31 July 2004.
Kaplan S L et al. Clin Infect Dis. 2005;40:1785-1791
© 2005 by the Infectious Diseases Society of America
Chung HJ et al. Journal of Clinical
Microbiology 2008. 46(3):991-995
Clues for CA-MRSA infection
In area of high prevalence
Highly susceptible groups
Contact history
?more pus and discharge due to presence of
PVL toxins
Antibiotic susceptibility profile
Thorough medical history and social history
Clinical examination: abscess, cellulitis
Risk evaluation: life threatening condition
(necrotizing fasciitis)
Appropriate culture before empirical
antibiotic treatment
Drainage of collections
Review culture results and clinical response
Report any confirmed case and contact
Follow up and decontimination
Decolonization in infected persons is indicated
in preventing recurrence and transmission of
Common decolonizing regime: 7.5%/10%
povidine iodine soap, 4% chlorhexidinegluconate liquid detergent, triclosan
preparations, mupirocin
Active contact tracing and MRSA decolonisation
with daily nasal mupirocin and chlorhexidine
detergent for showers for 5 days are offered to all
carrier is the current regime used in Hong Kong
CA-MRSA is an emerging epidemics
Skin and soft tissue infection is the most
common site of CA-MRSA infection
Prompt treatment is needed to prevent
bacteremia which can lead to life threatening
conditions such as necrotizing pneumonia
Incision and drainage is the most effect
treatment for abscesses
The choice of empirical antibiotics depends
on different localities as resistance profiles
varies a lot at different countries

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