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Keywords:

  • Community-associated;
  • epidemiology;
  • healthcare-associated;
  • infection;
  • MRSA;
  • Staphylococcus aureus;
  • USA300

Abstract

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

Clin Microbiol Infect

Abstract

The epidemic of USA300-0114 methicillin-resistant Staphylococcus aureus (MRSA) in the USA has been remarkable for its virulence and for its ability to cause infections in both the community and healthcare settings. Although it has mainly been associated with skin and soft tissue infections, particularly furunculosis, it has also caused severe life-threatening conditions such as necrotizing pneumonia, osteomyelitis, and septic arthritis. This strain or a closely related Latin American variant has now spread to multiple countries on five continents, where associated clinical and epidemiological features have been in keeping with those seen in the USA. Furthermore, it has become the dominant community-associated MRSA strain in five countries. It is now a major international epidemic strain, but whether it will supplant established community-associated strains in other countries remains to be seen.

The epidemiology of Staphylococcus aureus has changed remarkably in the early 21st century, with the rapid simultaneous emergence of virulent community-associated methicillin-resistant S. aureus (CA-MRSA) strains around the world [1]. Perhaps the most notable and well-documented epidemic has been that in the USA, caused by the USA300 strain.

The name USA300 was coined to describe the pulsed-field gel electrophoresis (PFGE) pattern of one of a number of methicillin-resistant S. aureus (MRSA) strains identified in the USA [2]. USA300 comprised a cluster of closely related PFGE patterns, including one variant, USA300-0114, that has been dominant in the CA-MRSA epidemic in the USA [3]. All variants belonged to ST8-MRSA-IV according to multilocus sequence typing and staphylococcal chromosomal cassette mec (SCCmec) typing. Outbreaks of USA300 began as early as 1999 in distinct populations such as prisoners, children in day care, athletes (particularly participants in contact sports), and military recruits, and also in community settings in otherwise healthy young people [4]. The infections associated with it included moderate to severe skin and soft tissue infections (SSTIs) and invasive infections, including necrotizing pneumonia, bone and joint infections, and necrotizing fasciitis.

The USA300 MRSA epidemic within the USA has been remarkable for the rapidity of its spread within the community, for its virulence, and for its subsequent emergence as a major cause of healthcare-associated (HA) infection [5–8]. The latter trend is of particular concern, as two independently developed mathematical models predict that successful CA-MRSA clones will come to dominate in healthcare settings [9,10]. The spread of USA300 has frequently been associated with fomites, and a number of studies suggest that it also has enhanced environmental survival and transmission properties [11–13]. Thus, USA300 is well adapted to spread and cause infections in the community and healthcare settings. This review will examine its impact beyond the borders of the USA.

Definitions

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

Although USA300 was originally defined by related PFGE patterns with >80% similarity [4], a number of other features define its epidemic methicillin-resistant variants. USA300-0114 and closely related variants predominantly carry the IVa subtype of SCCmec, spa type YHGFMBQBLO (t008; Ridom SpaServer), msrA-mediated macrolide resistance, and a number of virulence genes, including lukS-PV/lukF-PV and arcA, coding for Panton–Valentine leukocidin (PVL) and the arginine catabolic mobile element, respectively [3,14]. Isolates sharing these characteristics will be referred to as ‘USA300-0114’. A separate group of variants with six or fewer band differences on PFGE has been reported in Latin America, with the following characteristics: ST8, predominantly SCCmec type IVc, spa type t008, lukS-PV/lukF-PV present, arcA absent, and, commonly, tetracycline resistant caused by tetK [15]. This Latin American variant will be referred to as ‘USA300-LV’. Where typical PFGE, multilocus sequence typing or spa typing results and the presence of PVL genes are provided but SCCmec subtyping and the presence of arcA are not, isolates will be presumed to be USA300, and designated ‘USA300-P’.

Community-onset (CO) infections will, if possible, be divided into those without HA risk factors (CO-NR) and those with HA risk factors (CO-RF). The term hospital-onset (HO) will be used for infections occurring after 48 or 72 h of hospitalization as defined by the authors.

Canada

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

In Canada, USA300 is known as CMRSA-10, and has been the dominant CA-MRSA strain since 2004 [16–18]. An early report stated that USA300-P accounted for 16% of new cases in a study of MRSA infection or colonization in aboriginal hospital inpatients conducted from 1995 to 2002, although the year of first isolation was not stated [19]. Although it probably spread to Canada from the USA, most reported cases are autochthonous, where acquisition details are recorded [20–22]. In studies where isolates have undergone full molecular characterization, CMRSA-10 has been indistinguishable from USA300-0114 (Table 1). Although initially more prevalent in western Canada, it has become predominant in eastern centres as well [16,20,23]. Susceptibility to most non-β-lactam antimicrobials has been the norm. However, the majority of isolates have been resistant to erythromycin (but not to lincosamides), and some have also been resistant to ciprofloxacin [20,22,24–27].

Table 1.   Publications on USA300 cases by region
ReferencesPublishedStudy typeSample sizeCasesPeriodCountryI/AAcquisitionStrain
  1. A, autochthonous; CO, community onset; CO-NR, community onset with no healthcare-associated risk factors; CO-RF, community onset with healthcare-associated risk factors; HO, hospital onset; I, imported; NS, not stated.

North America
 [19]2006Prevalence survey148161995–2002CanadaNSNSUSA300-P
 [22]2006Outbreak investigation4240January–September 2004Canada36 A26 CO-NR, 11 CO-RF, 3 HOUSA300-0114
 [26]2007Outbreak investigation56145September 2004 to January 2005CanadaNSHOUSA300-0114
 [27]2007Case report11NSCanadaICO-RFUSA300-0114
 [21]2007Prevalence survey27118February–May 2005CanadaACOUSA300-0114
 [17]2008Case series1508272000–2006CanadaNS8 CO-NR, 12 CO-RF, 7 HOUSA300-P
 [23]2009Case–control study81682006–2007CanadaNSCOUSA300-P
 [20]2009Prevalence survey29929March–June 2007CanadaA7/9 CO-NR, 2/9 CO-RFUSA300-0114
 [24]2010Case report11NSCanadaNSCOUSA300-0114
 [16]2010Prevalence survey13 64811751995–2007CanadaNSNSUSA300-P
 [28]2011Prevalence survey12639April 2008 to March 2009CanadaAHOUSA300-P
 [25]2011Prevalence survey89104723Jully 2005 to June 2008CanadaNS3120 CO, 1010 HOUSA300-P
 [29]2011Prevalence survey18 5381652007–2009CanadaNSNSUSA300-0114
Latin America and the Caribbean
 [31]2008LetterNS152006–2007ColombiaANSUSA300-LV
 [15]2009Prevalence survey18901672006–2008Colombia, Ecuador, VenezuelaNSNSUSA300-0114, USA300-LV
 [36]2009Case series171February 2005 to March 2006BrazilICO-NRUSA300-P
 [32]2010Prevalence study25066June 2006 to December 2007ColombiaA40 CO-NR, 26 HOUSA300-LV
 [34]2011Prevalence survey803July 2009 to April 2010Trinidad & TobagoACOUSA300-0114, USA300-LV
 [82]2011Prevalence survey1437August 2007 to April 2008MartiniqueNSCOUSA300-P
 [37]2011Case series55February–March 2008MexicoNS4 CO-NR, 1 CO-RFUSA300-P
 [83]2011Prevalence survey3882008CubaNSNSUSA300-P
 [33]2011Case series32NSPeruICOUSA300-0114, USA300-LV
 [35]2012Prevalence survey50072007–2008ArgentinaNSCOUSA300-LV
Europe
 [84]2004Prevalence survey4982003The NetherlandsNSNSUSA300-P
 [85]2005Case report112003SwitzerlandICO-NRUSA300-P
 [55]2005Prevalence survey19712000, 2002The NetherlandsNSNSUSA300-P
 [86]2005Prevalence survey4132002–2004BelgiumNSCOUSA300-P
 [87]2006Family cluster study2792003–2004The NetherlandsNSNSUSA300-P
 [45]2007Prevalence survey2581999–2005Ireland2 I, 5 A7 CO-NR, 1 HOUSA300-0114
 [88]2007Prevalence survey18182000–2003Sweden1 ICO-NRUSA300-P
 [89]2007Case series652005–2007BulgariaNSCO-NRUSA300-P
 [90]2007Prevalence survey143122003–2004DenmarkA10 CO-NR, 2 CO-RFUSA300-P
 [91]2007Prevalence survey1001NSGermanyNSNSUSA300-P
 [56]2007Prevalence survey117232005–2006Germany9 ICO-NR or HOUSA300-0114
 [46]2007Surveillance report150092004–2006Austria3 I, 5 ACOUSA300-0114
 [92]2007Prevalence survey94302001–2006AustriaNSNSUSA300-P
 [39]2007Prevalence survey1986442000–2005Denmark11 I, 33 A24 CO-NR, 6 CO-RFUSA300-0114
 [43]2007Prevalence survey300402004–2005England and Wales8 I, 32 A32 COUSA300-0114
 [42]2008Outbreak investigation45112006The NetherlandsACOUSA300-0114
 [93]2008Case report11NSGermanyNSNSUSA300-0114
 [48]2008Case series5311September 2004 to September 2007Spain9 I, 2 ACO-NRUSA300-LV
 [51]2008Case series73122001–2007Spain10 I, 2 A11/12 CO, 1/12 HOUSA300-P
 [94]2008Prevalence survey4411991–2004FinlandNSNSUSA300-P
 [95]2008Case series20042000–2005SwitzerlandNSNSUSA300-P
 [96]2008Prevalence survey19442000–2006EnglandNSCOUSA300-P
 [61]2008Case report11NSItalyACO-NRUSA300-P
 [97]2008Prevalence survey104132000–2005SwedenNSCO-NRUSA300-P
 [57]2009Prevalence survey9423January 2005 to September 2007EnglandNSNSUSA300-P
 [54]2009Cohort study3703June 2003SpainNS2 CO-NR, 1 CO-RFUSA300-P
 [98]2009Genomic analysis1312004BelgiumNSCO-NRUSA300-LV
 [99]2009Prevalence survey7112004–2006EnglandNSCO-NRUSA300-0114
 [100]2009Prevalence survey275702005–2006England and Wales11 INSUSA300-0114, USA300-LV
 [101]2009Prevalence survey5352007Spain4 I, 1 ACO-NRUSA300-P
 [58]2009Case report112008BelgiumICO-NRUSA300-0114
 [49]2009Typing study80381999–2006Denmark21% I19 CO-NR, 7 CO-RF, 2 HOUSA300-0114
 [102]2009Prevalence survey1232006–2007ItalyNSCOUSA300-0114
 [103]2009Prevalence survey7072002–2007AustriaNSNSUSA300-P
 [47]2009Case series1955June 2006 to February 2008Italy2 I, 3 ACOUSA300-0114, USA300-LV
 [104]2009Prevalence survey298332004–2006FinlandNSCO-NRUSA300-P
 [40]2010Prevalence survey344621997–2007FranceANSUSA300-0114
 [105]2010Prevalence study6412005–2007ItalyNSNSUSA300-0114
 [50]2010Prevalence survey9673September 2006 to February 2007Europe (EARSS)NSCOUSA300-P
 [106]2010Prevalence survey5822002–2007FranceNSNSUSA300-P
 [53]2010Prevalence survey21672000–2004Sweden6 I, 1 ANSUSA300-P
 [107]2010Prevalence survey783January 2007 to December 2008SwitzerlandNSNSUSA300-P
 [108]2010Prevalence survey226302000–2008Iceland17 I, 13 ANSUSA300-P
 [109]2010Prevalence survey7662005–2008EnglandNSNSUSA300-0114
 [110]2010Case series5812002–2007EnglandNSCO-NRUSA300-P
 [59]2010Case report11NSSpainICOUSA300-0114
 [111]2011Prevalence survey2394March–June 2008EnglandNSNSUSA300-P
 [52]2011Prevalence survey1492222006–2009Austria (Upper)NSNSUSA300-P
 [112]2011Prevalence survey10842005–2006SpainNSCO-NRUSA300-P
 [113]2011Prevalence survey5112002–2004BelgiumICOUSA300-LV
 [60]2011Case series187April 2005 to October 2009ItalyNSNSUSA300-0114, USA300-LV
 [114]2011Prevalence survey3141January 2007 to January 2008The NetherlandsNSCOUSA300-LV
 [115]2011Prevalence survey3412December 2008 to December 2009ItalyNS7 CO, 5 HOUSA300-LV
 [41]2011Typing study40202005–2008Spain17 A, 3 INSUSA300-0114, USA300-LV
 [44]2012Prevalence survey41241978–2009SpainMost ANSUSA300-0114, USA300-LV
Middle East
 [64]2010Prevalence survey8466December 2007 to March 2009IraqNSNSUSA300-0114
 [65]2010Prevalence survey5912007–2008IsraelACOUSA300-P
 [63]2011Prevalence survey182144November 2007 to March 2009IraqINSUSA300-P
Western Pacific
 [67]2007Prevalence survey1381April 2004 to October 2005South KoreaINSUSA300-0114
 [68]2008Case report112007JapanICOUSA300-0114
 [66]2008Case series312007ChinaICO-NRUSA300-0114
 [74]2008Case report11NSAustraliaICOUSA300-P
 [73]2009Typing study7676July 2003 to February 2008AustraliaNSNSUSA300-0114, USA300-LV
 [75]2009Prevalence survey297862006AustraliaNSNSUSA300-P
 [72]2010Outbreak investigation1010September 2009JapanAHO/CO-RFUSA300-0114
 [70]2010Case report112008JapanACOUSA300-0114
 [69]2010Case report112008JapanICOUSA300-0114
 [116]2010Prevalence survey3002August–October 2008AustraliaNSCO-NRUSA300-P
 [71]2011Outbreak investigation442008JapanA1 CO, 3 HOUSA300-0114
 [78]2011Prevalence survey75454August or October 2010New ZealandNSNSUSA300-P
 [77]2011Prevalence survey399102007–2008SamoaANSUSA300-P

As in the USA, infection mainly manifests as moderate to severe SSTI, particularly furunculosis [20–23,28], and is more common among children and young adults [16,23,25]. Invasive infection has been reported less frequently, but has included cases of necrotizing pneumonia, empyema, bacteraemia, and infectious endocarditis [22,24,27,28]. An extensive outbreak was reported in 2004 in Calgary, Alberta among individuals with a history of illicit drug use, incarceration, or homelessness: there were 39 cases of SSTI, and one fatal case of necrotizing pneumonia [22]. Further investigation found a prevalence of colonization or infection of 5.5% in the marginalized population, and increased risk was associated with shared drug use between sex trade workers and clients or casual sex partners [21].

A population-based study of S. aureus bacteraemia in Calgary from 2000 to 2006 noted a major shift to CO CMRSA-10 cases from 2004, with a prevalence of 0.4/100000 [17]. A national prevalence survey conducted from 2007 to 2009 found that CMRSA-10 was responsible for 73.7% of CA-MRSA cases, 18.6% of all MRSA cases, and 4.6% of all S. aureus cases [29]. Another survey of all MRSA infections in Alberta from July 2005 to June 2008 found that CMRSA-10 caused 53% of cases and that the population-based prevalence was 16/100 000 in 2008 [25]. The proportion of HO cases in Alberta was 21%. The proportion was even higher in Vancouver in 2008–2009, with CMRSA-10 accounting for 32% of 126 incident cases of HO-MRSA infection or colonization [28]. Further evidence of the spread of CMRSA-10 into the healthcare setting is provided by multiple other reports confirming CO-RF and HO infection (Table 1). One hospital outbreak involving mothers and babies in a neonatal unit has also been reported [26]. Overall, the CMRSA-10 epidemic in Canada mirrors the experience with USA300-0144 in the USA.

Latin America and the Caribbean

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

The Latin American variant USA300-LV was first identified in Colombia as early as 2006, following an earlier report of two cases of CA-MRSA without details of genotyping [30,31]. Subsequently, USA300-LV has also been reported in Venezuela, Ecuador, Peru, Trinidad and Tobago, and Argentina (Fig. 1) [15,32–35]. Although USA300-LV is the predominant variant in these countries, USA300-0114 has also been reported in low numbers in all of these countries except Argentina. Autochthonous spread of USA300-LV has been well documented (Table 1). Imported cases have also been reported in this region: one caused by USA300-P from the USA in Brazil, and one each caused by USA300-0114 and USA300-LV from Puerto Rico and Ecuador, respectively, in Trinidad and Tobago [33,36]. Four cases of CO-NR infection and one of CO-RF infection caused by USA300-P have been reported from Mexico [37]. As the Mexican isolates showed 88% similarity to USA300-0114 by PFGE, resistance to erythromycin, predominant resistance to ciprofloxacin, and susceptibility to tetracycline, they are probably closely related to USA300-0114.

image

Figure 1.  Countries outside of the USA with reports of USA300 infection.

Download figure to PowerPoint

Although the majority of cases in Latin America have had their onset in the community (Table 1), 26 USA300-LV HO cases have been reported from Colombia [32]. They include nine cases of bacteraemia and 13 of surgical wound infection, with an overall mortality of 27%. Half of the patients were aged ≥60 years, and only 23% were aged <40 years. Where information has been available regarding CO infection, SSTI, particularly furunculosis, has predominated, although bacteraemia has also been reported [31,33,34,37]. Where susceptibility data are available for USA300-LV, resistance to tetracycline but not to other non-β-lactam antimicrobials is relatively common [15,32]. While age-related data for CO USA300-LV infection is generally lacking, the ages of two reported cases were 3 years and 39 years [33,34]. Although CA-MRSA accounts for 45% of CO S. aureus infection in Argentina, USA300-LV is relatively uncommon there, reprsenting only 1.4% of 500 CO-MRSA isolates from a survey of infections in children in 2007–2008 [35]. The situation in Colombia, Ecuador and Venezuela is very different: there, USA300-LV is the dominant CA-MRSA strain, accounting for 10.6% of consecutive S. aureus isolates in hospital laboratories [15]. Finally, a recent study of porcine carriage of MRSA has raised the possibility of an animal reservoir: one isolate of USA300-LV was identified from nasal swabs of 120 rural scavenging pigs in Peru in 2009 [38].

Europe

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

USA300 was first recognized in Europe in Denmark in 2000 [39]. Over 50 reports from 15 countries have followed, including cases causedby both USA300-0114 and USA300-LV (Table 1; Fig. 1). While imported cases have been reported frequently, autochthonous spread of USA300-0114 has also been recorded in Austria, Denmark, England, France, Ireland, The Netherlands, and Spain [39–46]. Autochthonous spread of USA300-LV is more limited, having been reported in only Italy and Spain [41,44,47,48]. Although USA300 MRSA isolates in Europe have been susceptible to most non-β-lactam antimicrobials, USA300-0114 isolates have generally been resistant to erythromycin, and frequently resistant to fluoroquinolones [44,49]. USA300-LV isolates have been resistant to tetracycline in less than half of cases, and to mupirocin or fusidic acid occasionally [44,48]. Although population-based prevalence data have been lacking, only three (0.3%) isolates from S. aureus bacteraemia cases in 26 European countries between September 2006 and February 2007 were consistent with USA300 MRSA [50]. By comparison, only two isolates of ‘European’ ST80 CA-MRSA were detected in the same survey. Isolates consistent with USA300 are the most common PVL-positive MRSA strains in Spain, and, among these, USA300-LV is predominant [41,44,48,51]. Unlike the situation in Canada, USA300 generally makes up only a small proportion of all clinical MRSA isolates in Europe, ranging from 0.8% to 3.5% in various countries [39,44,45,47,51–55].

As elsewhere, furunculosis and other SSTIs have been the major clinical manifestations of infection with both USA300-0114 and USA300-LV in Europe [44,45,48,56]. Cases of severe invasive infection, including necrotizing pneumonia, meningitis, osteomyelitis, and deep vein thrombosis, have also been reported [56–61]. One community outbreak caused by USA300-0114 related to a beauty salon has been reported from The Netherlands [42]. The great majority of cases have had their onset in the community, and CO-NR infections are common among these (Table 1). Although HO cases have been documented, no hospital outbreaks have been reported. Finally, one remarkable case of USA300-P infection in a dog has recently been reported from France [62]. The isolate from a surgical wound infection was arginine catabolic mobile element-negative, and therefore may be related to USA300-LV. However, a family member of the treating veterinarian had recently undergone prolonged hospitalization in the USA. SCCmec subtyping was not reported.

Middle East

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

Two reports of cases of USA300 infection among USA military personal have come from combat support hospitals in Iraq [63,64]. USA300-0114 was definitively identified in one of them, and constituted 79% of 84 MRSA isolates [64]. Ninety-two per cent of isolates were resistant to erythromycin, 3% to clindamycin, 41% to levofloxacin, and 1% to tetracycline. Most cases have been wound infections and furunculosis [63]. The only other report from the Middle East was from the Western Galilee region of Israel. The case was an autochthonous one consistent with USA300-P resistant only to β-lactams and erythromycin in a 9-month-old child with post-varicella furunculosis [65].

Western Pacific

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

USA300-0114 has been reported in the Western Pacific from China, South Korea, Japan, Australia, New Zealand, and Samoa (Table 1; Fig. 1). Single cases of imported infection were reported in South Korea and China in 2004–2005 and 2007, respectively [66,67]. The Chinese case was of furunculosis in a 39-year-old Japanese man who had recently visited Thailand and had no HA risk factors. The first imported case occurring in Japan was in Tokyo in 2007 in a 3-month-old, US-born female with CO furunculosis [68]. Two additional cases occurred in 2008 in Saitama: an imported CO case of furunculosis and epidural abscess in a 25-year-old American woman, and an autochthonous CO case of cellulitis and bacteraemia in an 11-month-old girl [69,70]. Two HA outbreaks have also been reported in Japan: one in Okinawa in 2008, involving a CO index case and three healthcare workers, all with furunculosis, and one in Kyoto in 2009 involving both hospitalized patients and healthcare workers, including cases of furunculosis, pneumonia, and catheter-related bacteraemia [71,72]. The outbreak strain in the latter was unusual in being resistant only to levofloxacin. Where tested, isolates from the other north-western Asian reports were all resistant to erythromycin. Some were resistant to ciprofloxacin, and the Okinawa strain was also resistant to clindamycin, consistent with a constitutive MLSB phenotype.

USA300 first appeared in Australia in 2003: 76 isolates from 72 cases in Perth, Western Australia, were collected between July 2003 and February 2008 [73]. The majority conformed to USA300-0114, but 12 lacked arcA and were therefore likely to be USA300-LV. Five of these isolates carried tetK, which is unusual in USA300-0114. Most USA-0114 isolates carried msrA (57/64), as did four USA300-LV isolates. Most cases (94%) were of SSTI. On the east coast, USA300-P was reported in 2008 in an imported case of furunculosis in a US resident visiting Sydney [74]. Two USA300-P isolates identified in a prevalence survey conducted in Queensland in 2008 represented <0.1% of S. aureus non-duplicate clinical isolates [74]. Biennial national prevalence surveys of clinical S. aureus isolates from outpatients conducted from 2000 to 2010 identified USA300-P isolates from 2004 onwards [75,76]. Most isolates were from New South Wales, but some were also identified in Queensland, Victoria, Western Australia, and the Northern Territory. They represented only 0.8–1.8% of MRSA isolates and 0.1–0.3% of S. aureus isolates in the various surveys. The six isolates from the 2010 survey were all resistant to erythromycin, one was additionally resistant to mupirocin, and two were additionally resistant to ciprofloxacin. They were susceptible to the remaining 13 non-β-lactam antimicrobials tested.

Prevalence surveys identifying cases of USA300 MRSA infection have also been conducted in New Zealand and Samoa. A Samoan study conducted in 2007–2008 showed that USA300-P represented 29% of 34 MRSA isolates and 5% of 187 S. aureus isolates from autochthonous cases of SSTI [77]. Of note, it was the most common MRSA strain, ahead of the Queensland clone (ST93-MRSA-IV–26%) and the south-western Pacific clone (ST30-MRSA-IV–12%). The isolates were all resistant to ciprofloxacin, and most were also resistant to erythromycin. In New Zealand, USA300-P represented 7.2% of 740 MRSA isolates referred to a reference laboratory as part of a national survey in 2010 [78]. Fifty-seven per cent of cases were CO-MRSA and 82% of patients were aged <60 years. USA300-P was first identified in Dunedin in 2004, and has since been isolated throughout the country.

Discussion

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References

International and intercontinental spread of epidemic S. aureus strains, including MRSA, is not a new phenomenon [79,80], but is arguably being facilitated by increasing volumes of international travel and migration in the 21st century. In this context, the rapid international spread of USA300 provides a good example. Within a few years of its first description, it has been reported in 36 countries on five continents (Table 1; Fig. 1). Furthermore, autochthonous acquisition has been documented in Canada, 10 European countries, Colombia, Trinidad and Tobago, Israel, Japan, and Samoa. This has been a cause for concern, given its virulence and epidemic potential in both community and healthcare settings in the USA.

The prevalence of USA300 currently remains low in most countries. Notable exceptions are Canada, Samoa, and the Andean countries of Columbia, Ecuador, and Venezuela. USA300-0114 has become the dominant CA-MRSA strain in Canada, which is not surprising, given its shared open border with the USA. It has also been identified definitively in countries in Europe (10), Latin American (4), the Western Pacific (4), and the Caribbean (1) (Table 1). The surprisingly high prevalence of USA300-P in Samoa may similarly be explained by its proximity to and close cultural links with American Samoa. Furthermore, many of the isolates there were indistinguishable from the USA300-0114 pulsotype, and had a resistance profile suggestive of that strain [77]. The Andean countries, on the other hand, appear to be the epicentre for the emergence of the variant USA300-LV [15]. It has also been definitively detected in two other Spanish-speaking countries in Latin America, in the Caribbean, in six European countries, and in Australia (Table 1).

The clinical manifestations of USA300-0114, USA300-LV and USA300-P around the world are all similar to those experienced in the USA with USA300-0114. As detailed above, most cases have been of SSTI, particularly furunculosis, but severe invasive infections have also regularly been reported. Although the mortality rate was remarkably high in Columbian HO infections, only four other fatal cases have been reported [22,27,32,43,58]. A predilection for children and younger adults has been noted frequently. Spread into healthcare settings has also been frequent, although only USA300-0114 has been associated with reports of outbreaks (Table 1). Reports of infection with USA300-P in a dog in France and of carriage of USA300-LV in a scavenging pig in Peru were exceptional, although isolations of USA300-0114 from a dog and a pig have also been reported in the USA [38,62,81].

In conclusion, USA300 MRSA has become a major international epidemic clone, commonly causing both CO and HO infections, and is now the dominant CA-MRSA strain in five countries outside of the USA. Whether it will replace established CA-MRSA in other countries remains to be seen. Regardless of this, experience to date suggests that the USA300 epidemic will continue for some time to come.

References

  1. Top of page
  2. Abstract
  3. Definitions
  4. Canada
  5. Latin America and the Caribbean
  6. Europe
  7. Middle East
  8. Western Pacific
  9. Discussion
  10. Transparency Declaration
  11. References
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    Vandenesch F, Naimi T, Enright MC et al. Community-acquired methicillin resistant Staphylococcus aureus carrying Panton–Valentine leukocidin genes: worldwide emergence. Emerg Infect Dis 2003; 9: 978984.
  • 2
    McDougal LK, Steward CD, Killgore GE et al. Pulsed-field gel electrophoresis typing of oxacillin-resistant Staphylococcus aureus isolates from the United States: establishing a national database. J Clin Microbiol 2003; 41: 51135120.
  • 3
    Tenover FC, McDougal LK, Goering RV et al. Characterization of a strain of community-associated methicillin-resistant Staphylococcus aureus widely disseminated in the United States. J Clin Microbiol 2006; 44: 108118.
  • 4
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