EID Journal Home > Volume 13, Number 8-August 2007

Volume 13, Number 8-August 2007
Skin and Soft Tissue Infections Caused by Methicillin-Resistant Staphylococcus aureus USA300 Clone

Jennifer K. Johnson,*  Tina Khoie,* Simone Shurland,* Kristen Kreisel,* O. Colin Stine,* and Mary-Claire Roghmann*†
*University of Maryland School of Medicine, Baltimore, Maryland, USA; and †Veterans Affairs Maryland Health Care
System, Baltimore, Maryland, USA

Until recently, methicillin-resistant Staphylococcus aureus (MRSA) has caused predominantly healthcare-associated
infections. We studied MRSA infections and overall skin and soft tissue infections (SSTIs) in outpatients receiving care
at the Baltimore Veterans Affairs Medical Center Emergency Care Service during 2001-2005. We found an increase in
MRSA infections, from 0.2 to 5.9 per 1,000 visits (p<0.01); most were community-associated SSTIs. Molecular typing
showed that >80% of MRSA infections were caused by USA300. In addition, SSTI visits increased from 20 to 61 per
1,000 visits (p<0.01). The proportion of SSTI cultures that yielded MRSA increased from 4% to 42% (p<0.01), while the
proportion that yielded methicillin-sensitive S. aureus remained the same (10% to 13%, p = 0.5). The increase in
community-associated MRSA infections and the overall increase in SSTIs in our population suggest that USA300 is
becoming more virulent and has a greater propensity to cause SSTIs.

suggested citation for this article: Bartels MD, Boye K, Larsen AR, Skov R, Westh H.

Rapid increase of genetically diverse methicillin-resistant Staphylococcus aureus, Copenhagen,

Denmark. Emerg Infect Dis. 2007 Oct; [Epub ahead of print]
Rapid Increase of Genetically Diverse Methicillin-Resistant Staphylococcus aureus, Copenhagen, Denmark
Mette Damkjær Bartels,* Kit Boye,* Anders Rhod Larsen,† Robert Skov,† and Henrik Westh*†
*Hvidovre Hospital, Hvidovre, Denmark; and †Statens Serum Institut, Copenhagen, Denmark

In Copenhagen, methicillin-resistant Staphylococcus aureus (MRSA) accounted for <15 isolates per year
during 1980-2002. However, since 2003 an epidemic increase has been observed, with 33 MRSA cases
in 2003 and 110 in 2004. We analyzed these 143 cases epidemiologically and characterized isolates by
pulsed-field gel electrophoresis, Staphylococcus protein A (spa) typing, multilocus sequence typing,
staphylococcal chromosome cassette (SCC) mec typing, and detection of Panton-Valentine leukocidin
(PVL) genes. Seventy-one percent of cases were community-onset MRSA (CO-MRSA); of these, 36%
had no identified risk factors. We identified 29 spa types (t) and 16 sequence types (STs) belonging to 8
clonal complexes and 3 ST singletons. The most common clonal types were t024/ST8-IV, t019/ST30-IV,
t044/ST80-IV, and t008/ST8-IV (USA300). A total of 86% of isolates harbored SCCmec IV, and 44% had
PVL. Skin and soft tissue infections dominated. CO-MRSA with diverse genetic backgrounds is rapidly
emerging in a low MRSA prevalence area.

For many years, methicillin-resistant Staphylococcus aureus (MRSA) has been a serious
and common nosocomial pathogen in hospitals outside the Nordic countries and the Netherlands
(1). Community-onset MRSA (CO-MRSA) was first reported in Western Australia in the early
1990s (2) and has, especially during the past 5 years, emerged as a global problem (1,3). COMRSA
in the United States has mostly been caused by the Panton-Valentine leukocidin (PVL)-
positive clones USA400 (sequence type [ST]1) and more recently by USA300 (ST8) (1,4-7). In
Europe the increase in CO-MRSA has mostly been attributed to the PVL-positive ST80 clone

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(3,8). In Denmark, since 1980, MRSA has accounted for <100 MRSA isolates per year
nationwide (www.danmap.org/pdffiles/danmap_2005.pdf). At our laboratory, MRSA has been
isolated from <15 patients per year until 2002. Approximately half of the MRSA cases found in
Denmark during these years were imported, i.e., through patients transferred from foreign
hospitals (9).

Since 2003 the number of MRSA-positive persons increased both nationally and in
Copenhagen. Nationally, the number increased from 50-105 new cases per year to 243 in 2003,
549 in 2004, and 864 in 2005. At Hvidovre Hospital, we found MRSA in 5 persons in 2001, 14
in 2002, 33 in 2003, 110 in 2004, and 170 in 2005. We describe the epidemiology of the
emergence of MRSA in Copenhagen in 2003 and 2004 and characterize the genetic background
of the isolates.


Staphylococci can cause a wide variety of diseases in humans and other animals either through toxin production or
invasion. Staphylococcal toxins are a common cause of food poisoning. The bacteria grow in improperly stored food.
Although the cooking process kills them, the enterotoxins are heat resistant and can survive boiling for several minutes.
Staphylococci can grow in foods with relatively low water activity (such as cheese and salami).

One pathogenic species is Staphylococcus aureus, which can infect wounds. These bacteria can survive on dry
surfaces, increasing the chance of transmission. Of this type, Methicillin-resistant Staphylococcus aureus (MRSA) has
recently become a major cause of hospital-acquired infections and is being recognized with increasing frequency in
community acquired infections. S. aureus is also implicated in toxic shock syndrome; during the 1980s some tampons
allowed the rapid growth of S. aureus, which released toxins that were absorbed into the bloodstream. Any S. aureus
infection can cause the staphylococcal scalded skin syndrome, a cutaneous reaction to exotoxin absorbed into the
bloodstream. It can also cause a type of septicaemia called pyaemia.

The coagulase positive Staphylococcus that inhabits and sometimes infects the skin of domestic dogs and cats is
Staphylococcus intermedius. This organism, too, can carry the genetic material that imparts multiple bacterial
resistance. It is rarely implicated in infections in humans, as a zoonosis.

S. epidermidis, a coagulase-negative staphylococcus species, is a commensal of the skin, but can cause severe
infections in immune suppressed patients and those with central venous catheters.

S. saprophyticus, another coagulase-negative species, is predominantly implicated in genitourinary tract infections in
sexually active young women.

In recent years several other Staphylococcus species have been implicated in human infections, notably S.
lugdunensis, S. schleiferi, and S. caprae.

Staphylococcus can also be found on the tips of the fingers. Most commonly it is found on the index finger as well as
the thumb. This infection is known as a felon. As are many other "staph" infections this is very painful and can be
treated with antibiotics.

Necrotizing fasciitis  is the result of an invasive bacterial infection that destroys deep soft tissue .
Staphylococcus genus: S. aureus is a leading cause of soft tissue infections, as well as toxic shock syndrome (TSS)
and scalded skin syndrome. pathogenic effects of Staph are mainly asssociated with the toxins it produces. it is not
uncommon for an infected site to contain no viable Staph cells. The S. aureus enterotoxin causes quick onset food
poisoning which can lead to cramps and severe vomiting. microbes also secrete leukocidin, a toxin which destroys white
blood cells and leads to the formation of pus and acne.  S. aureus has been found to be the causative agent in such
ailments as pneumonia, meningitis, boils, arthritis, and osteomyelitis (chronic bone infection).
S. epidermis is an opportunistic pathogen which is a normal resident of human skin. Those susceptible to infection by
the bacterium are IV drug users, newborns, elderly, and those using catheters or other artificial appliances