Rapid Increase of Genetically Diverse Methicillin-resistant Staphylococcus Aureus, Copenhagen, Denmark

Mette Damkjær Bartels; Kit Boye; Anders Rhod Larsen; Robert Skov; Henrik Westh


Emerging Infectious Diseases. 2007;13(10):1533-1540. 

In This Article

Abstract and Introduction


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] CO-MRSA 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).[1,4,5,6,7] In Europe the increase in CO-MRSA has mostly been attributed to the PVL-positive ST80 clone.[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.


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