Spread of a Methicillin-Resistant Staphylococcus aureus ST80-IV Clone in a Danish Community

Is decolonisation to prevent PVL-positive Staphylococcus aureus infection in the population effective? A systematic review

INTRODUCTION

Panton-Valentine Leukocidin (PVL) producing Staphylococcus aureus is associated with recurrent skin and soft tissue infections and occasionally invasive infections. There is limited evidence to support current public health guidance on decolonisation of cases and household contacts.

METHODS

This systematic review (CRD42020189906) investigated the efficacy of decolonisation against PVL-positive S. aureus to inform future public health practice. It included studies of cases with PVL-positive infections providing information on the efficacy of decolonisation of cases, carriers, or contacts of cases. Studies were assessed for the risk of bias using the GRADE approach and summarised to inform a narrative synthesis.

RESULTS

The search identified 20, mostly observational, studies with small samples and lacking control groups. Studies with longer follow-ups found that, while early post-decolonisation screening was negative for most individuals, testing over subsequent months identified re-colonisation in some. There is no high quality evidence to show whether decolonisation is effective in reducing (re)infection or long-term carriage of PVL-positive S. aureus and the low quality evidence available indicates it may not be effective in eradicating carriage or reducing future disease. Furthermore, there may be risks associated with decolonisation, for example, potentially increased risk of infection from other microbes, opportunity costs and negative impacts of repeated testing for asymptomatic carriage.

CONCLUSIONS

Further research is required to better understand what affects the ability of decolonisation efforts to reduce risk to cases and their contacts, including strain, host and environmental factors.

Methicillin-Resistant Staphylococcus aureus ST80 Clone: A Systematic Review

This review assessed the molecular characterization of the methicillin-resistant Staphylococcus aureus (MRSA)-ST80 clone with an emphasis on its proportion of total MRSA strains isolated, PVL production, spa-typing, antibiotic resistance, and virulence. A systematic review of the literature was conducted on MRSA-ST80 clone published between 1 January 2000 and 31 August 2019. Citations were chosen for a review of the full text if we found evidence that MRSA-ST80 clone was reported in the study. For each isolate, the country of isolation, the sampling period, the source of isolation (the type of infection, nasal swabs, or extra-human), the total number of MRSA strains isolated, number of MRSA-ST80 strains, antibiotic resistance patterns, PVL production, virulence genes, and spa type were recorded. The data from 103 articles were abstracted into an Excel database. Analysis of the data showed that the overall proportion of MRSA-ST80 has been decreasing in many countries in recent years. The majority of MRSA-ST80 were PVL positive with spa-type t044. Only six reports of MRSA-ST80 in extra-human niches were found. This review summarizes the rise of MRSA-ST80 and the evidence that suggests that it could be in decline in many countries.

Evidence for Community Transmission of Community-Associated but Not Health-Care-Associated Methicillin-Resistant Staphylococcus Aureus Strains Linked to Social and Material Deprivation: Spatial Analysis of Cross-sectional Data

BACKGROUND

Identifying and tackling the social determinants of infectious diseases has become a public health priority following the recognition that individuals with lower socioeconomic status are disproportionately affected by infectious diseases. In many parts of the world, epidemiologically and genotypically defined community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) strains have emerged to become frequent causes of hospital infection. The aim of this study was to use spatial models with adjustment for area-level hospital attendance to determine the transmission niche of genotypically defined CA- and health-care-associated (HA)-MRSA strains across a diverse region of South East London and to explore a potential link between MRSA carriage and markers of social and material deprivation.

METHODS AND FINDINGS

This study involved spatial analysis of cross-sectional data linked with all MRSA isolates identified by three National Health Service (NHS) microbiology laboratories between 1 November 2011 and 29 February 2012. The cohort of hospital-based NHS microbiology diagnostic services serves 867,254 usual residents in the Lambeth, Southwark, and Lewisham boroughs in South East London, United Kingdom (UK). Isolates were classified as HA- or CA-MRSA based on whole genome sequencing. All MRSA cases identified over 4 mo within the three-borough catchment area (n = 471) were mapped to small geographies and linked to area-level aggregated socioeconomic and demographic data. Disease mapping and ecological regression models were used to infer the most likely transmission niches for each MRSA genetic classification and to describe the spatial epidemiology of MRSA in relation to social determinants. Specifically, we aimed to identify demographic and socioeconomic population traits that explain cross-area extra variation in HA- and CA-MRSA relative risks following adjustment for hospital attendance data. We explored the potential for associations with the English Indices of Deprivation 2010 (including the Index of Multiple Deprivation and several deprivation domains and subdomains) and the 2011 England and Wales census demographic and socioeconomic indicators (including numbers of households by deprivation dimension) and indicators of population health. Both CA-and HA-MRSA were associated with household deprivation (CA-MRSA relative risk [RR]: 1.72 [1.03-2.94]; HA-MRSA RR: 1.57 [1.06-2.33]), which was correlated with hospital attendance (Pearson correlation coefficient [PCC] = 0.76). HA-MRSA was also associated with poor health (RR: 1.10 [1.01-1.19]) and residence in communal care homes (RR: 1.24 [1.12-1.37]), whereas CA-MRSA was linked with household overcrowding (RR: 1.58 [1.04-2.41]) and wider barriers, which represent a combined score for household overcrowding, low income, and homelessness (RR: 1.76 [1.16-2.70]). CA-MRSA was also associated with recent immigration to the UK (RR: 1.77 [1.19-2.66]). For the area-level variation in RR for CA-MRSA, 28.67% was attributable to the spatial arrangement of target geographies, compared with only 0.09% for HA-MRSA. An advantage to our study is that it provided a representative sample of usual residents receiving care in the catchment areas. A limitation is that relationships apparent in aggregated data analyses cannot be assumed to operate at the individual level.

CONCLUSIONS

There was no evidence of community transmission of HA-MRSA strains, implying that HA-MRSA cases identified in the community originate from the hospital reservoir and are maintained by frequent attendance at health care facilities. In contrast, there was a high risk of CA-MRSA in deprived areas linked with overcrowding, homelessness, low income, and recent immigration to the UK, which was not explainable by health care exposure. Furthermore, areas adjacent to these deprived areas were themselves at greater risk of CA-MRSA, indicating community transmission of CA-MRSA. This ongoing community transmission could lead to CA-MRSA becoming the dominant strain types carried by patients admitted to hospital, particularly if successful hospital-based MRSA infection control programmes are maintained. These results suggest that community infection control programmes targeting transmission of CA-MRSA will be required to control MRSA in both the community and hospital. These epidemiological changes will also have implications for effectiveness of risk-factor-based hospital admission MRSA screening programmes.

Political Versus Epidemiological Correctness

In the March issue of the journal, the Joint SHEA and APIC Task Force indicates that the Society for Healthcare Epidemiology of America (SHEA) and the Association for Professionals in Infection Control and Epidemiology (APIC) support the use of active detection and isolation (ADI) for controlling nosocomial infections due to methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) “in appropriate circumstances, as recommended in previously published guidelines”1(p250) (those published by SHEA and the Healthcare Infection Control Practices Advisory Committee [HICPAC]), but that SHEA and APIC oppose the use of legislation for mandating any infection control approach, including this one as tried in 2006 in Illinois and Maryland.

Both supporters and opponents of controlling MRSA and VRE with ADI probably will agree that legislation is not the optimal way to control nosocomial infections in general, but this position statement undoubtedly will please the latter more than it does the former because the SHEA/APIC Task Force argues that ADI is not ready for routine use throughout all healthcare facilities, directly opposing the position of the original SHEA guideline. As an author of that SHEA guideline, I would like to comment. First, the new position seems politically correct (since most infection control professionals have not yet bothered using ADI to control MRSA and VRE), but many of the planks of the SHEA/APIC Task Force position statement are misleading.

Community-associated methicillin-resistant Staphylococcus aureus clonal complex 80 type IV (CC80-MRSA-IV) isolated from the Middle East: a heterogeneous expanding clonal lineage

Background

The emergence of community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) has caused a change in MRSA epidemiology worldwide. In the Middle East, the persistent spread of CA-MRSA isolates that were associated with multilocus sequence type (MLST) clonal complex 80 and with staphylococcal cassette chromosome mec (SCCmec) type IV (CC80-MRSA-IV), calls for novel approaches for infection control that would limit its spread.

Methodology/Principal Findings

In this study, the epidemiology of CC80-MRSA-IV was investigated in Jordan and Lebanon retrospectively covering the period from 2000 to 2011. Ninety-four S. aureus isolates, 63 (67%) collected from Lebanon and 31 (33%) collected from Jordan were included in this study. More than half of the isolates (56%) were associated with skin and soft tissue infections (SSTIs), and 73 (78%) were Panton-Valentine Leukocidin (PVL) positive. Majority of the isolates (84%) carried the gene for exofoliative toxin d (etd), 19% had the Toxic Shock Syndrome Toxin-1 gene (tst), and seven isolates from Jordan had a rare combination being positive for both tst and PVL genes. spa typing showed the prevalence of type t044 (85%) and pulsed-field gel electrophoresis (PFGE) recognized 21 different patterns. Antimicrobial susceptibility testing showed the prevalence (36%) of a unique resistant profile, which included resistance to streptomycin, kanamycin, and fusidic acid (SKF profile).

Conclusions

The genetic diversity among the CC80 isolates observed in this study poses an additional challenge to infection control of CA-MRSA epidemics. CA-MRSA related to ST80 in the Middle East was distinguished in this study from the ones described in other countries. Genetic diversity observed, which may be due to mutations and differences in the antibiotic regimens between countries may have led to the development of heterogeneous strains. Hence, it is difficult to maintain “the European CA-MRSA clone” as a uniform clone and it is better to designate as CC80-MRSA-IV isolates.

The role of international travel in the spread of methicillin-resistant Staphylococcus aureus

BACKGROUND

Increasing international travel has facilitated the transmission of various multidrug-resistant bacteria-including methicillin-resistant Staphylococcus aureus (MRSA)-across continents. Individuals may acquire MRSA from the community, healthcare facilities, or even from animal exposure. Skin contact with colonized individuals, fomites, or animals during an overseas trip may result in either asymptomatic colonization or subsequent clinically significant MRSA disease. MRSA strains that harbor the Panton-Valentine leucocidin toxin are particularly associated with community transmission and may potentially have enhanced virulence resulting in serious skin and soft tissue infections or even necrotizing pneumonia. More importantly, secondary transmission events upon return from traveling have been documented, leading to potentially detrimental outbreaks within the community or the healthcare setting. We sought to review the existing literature relating to the role of various aspects of travel in the spread of MRSA. Risk factors for acquiring MRSA during travel together with the need for targeted screening of high-risk individuals will also be explored.

METHODS

Data for this article were identified via PubMed searches using a combination of search terms: "methicillin resistance," "MRSA," "livestock-associated MRSA," "community-associated MRSA," "travel," and "outbreak." The relevant articles were extensively perused to determine secondary sources of data.

RESULTS AND CONCLUSIONS

Our review of the current literature suggests that international travel plays a significant role in the transmission of MRSA, potentially contributing to the replacement of existing endemic MRSA with fitter and more transmissible strains. Therefore, selective and targeted screening of travelers with risk factors for MRSA colonization may be beneficial. Healthcare professionals and patients should be considered for screening if they were to return from endemic areas, with the former group decolonized before returning to patient care work, in order to reduce the transmission of MRSA to vulnerable patient populations.

Management of healthcare-associated methicillin-resistantStaphylococcus aureus

Healthcare-associated methicillin-resistant Staphylococcus aureus is a major cause of nosocomial infections worldwide, with significant attributable morbidity and mortality in addition to pronounced healthcare costs. Treatment results with vancomycin--the current recommended antibiotic for serious methicillin-resistant S. aureus infections--have not been impressive. The recent availability of effective antimicrobial agents other than glycopeptides, such as linezolid and daptomycin, as well as the anticipated approval of newer agents with diverse mechanisms of action, has somewhat ameliorated the threat posed by this organism. However, these drugs are expensive, and there is still no overall satisfactory strategy for reducing the incidence of healthcare-associated methicillin-resistant S. aureus in endemic regions. Although early results with the Society for Healthcare Epidemiology of America guidelines give cause for cautious optimism, long-term experience is lacking, and it is likely that these guidelines will have to be adapted according to local conditions and resources before implementation. Trends to keep in mind when considering the problem of healthcare-associated methicillin-resistant S. aureus include the advent of community-associated methicillin-resistant S. aureus, and the propensity of S. aureus to evolve and acquire resistance determinants over time. This was last vividly demonstrated by the handful of vancomycin-resistant S. aureus isolated recently, which had acquired the vancomycin resistance gene from vancomycin-resistant enterococci.

Methicillin-Resistant Staphylococcus aureus Associated with Animals and Its Relevance to Human Health

Staphylococcus aureus is a typical human pathogen. Some animal S. aureus lineages have derived from human strains following profound genetic adaptation determining a change in host specificity. Due to the close relationship of animals with the environmental microbiome and resistome, animal staphylococcal strains also represent a source of resistance determinants. Methicillin-resistant S. aureus (MRSA) emerged 50 years ago as a nosocomial pathogen but in the last decade it has also become a frequent cause of infections in the community. The recent finding that MRSA frequently colonizes animals, especially livestock, has been a reason for concern, as it has revealed an expanded reservoir of MRSA. While MRSA strains recovered from companion animals are generally similar to human nosocomial MRSA, MRSA strains recovered from food animals appear to be specific animal-adapted clones. Since 2005, MRSA belonging to ST398 was recognized as a colonizer of pigs and human subjects professionally exposed to pig farming. The “pig” MRSA was also found to colonize other species of farmed animals, including horses, cattle, and poultry and was therefore designated livestock-associated (LA)-MRSA. LA-MRSA ST398 can cause infections in humans in contact with animals, and can infect hospitalized people, although at the moment this occurrence is relatively rare. Other animal-adapted MRSA clones have been detected in livestock, such as ST1 and ST9. Recently, ST130 MRSA isolated from bovine mastitis has been found to carry a novel mecA gene that eludes detection by conventional PCR tests. Similar ST130 strains have been isolated from human infections in UK, Denmark, and Germany at low frequency. It is plausible that the increased attention to animal MRSA will reveal other strains with peculiar characteristics that can pose a risk to human health.

Emergence of MRSA of unknown origin in the Netherlands

The Netherlands is known for its low methicillin-resistant Staphylococcus aureus (MRSA) prevalence. Yet MRSA with no link to established Dutch risk factors for acquisition, MRSA of unknown origin (MUO), has now emerged and hampers early detection and control by active screening upon hospital admittance. We assessed the magnitude of the problem and determined the differences between MUO and MRSA of known origin (MKO) for CC398 and non-CC398. National MRSA Surveillance data (2008-2009) were analysed for epidemiological determinants and genotypic characteristics (Panton-Valentine leukocidin, spa). A quarter (24%) of the 5545 MRSA isolates registered were MUO, i.e. not from defined risk groups. There are two genotypic MUO groups: CC398 MUO (352; 26%) and non-CC398 MUO (998; 74%). CC398 MUO needs further investigation because it could suggest spread, not by direct contact with livestock (pigs, veal calves), but through the community. Non-CC398 MUO is less likely to be from a nursing home than non-CC398 MKO (relative risk 0.55; 95% CI 0.42-0.72) and Panton-Valentine leukocidin positivity was more frequent in non-CC398 MUO than MKO (relative risk 1.19; 95% CI 1.11-1.29). Exact transmission routes and risk factors for non-CC398 as CC398 MUO remain undefined.

High prevalence of methicillin-resistant Staphylococcus aureus clone ST80-IV in hospital and community settings in Algiers

USA300 is an epidemic community-acquired methicillin-resistant Staphylococcus aureus (C-MRSA) clone in the USA, whereas the European C-MRSA clone ST80-IV has mainly a sporadic diffusion in Europe. The prevalence of European clone ST80-IV in Algeria is poorly documented. We prospectively studied S. aureus infections at Mustapha Bacha hospital in Algiers over a 20-month period. S. aureus nasal colonization was studied during a further 6-month period. The European clone ST80-IV was responsible for more than one-third of both community infections (35.7%) and hospital infections (35.8%). Panton-Valentine leukocidin (PVL)-positive MRSA isolated from hospital inpatients were resistant to multiple antibiotics, including fluoroquinolones in 44.9% of cases. The PVL-positive MRSA nasal carriage rate was high among patients and staff in the dermatology unit (8.7% and 18.5%, respectively), but low (2.7%) among patients attending the outpatient clinic. The European PVL-positive C-MRSA clone ST80-IV is widespread in the Algiers hospital and community settings.

Staphylococcus aureus skin and soft tissue infections in primary healthcare in Denmark: a 12-year population-based study

A rise in community-onset Staphylococcus aureus infections has been observed in European countries. To ascertain secular trends of S. aureus infections in primary healthcare in Denmark, we conducted this register-based study in the North Denmark region, during the period 1997-2008. We identified all skin and mucosa specimens obtained by general practitioners and all prescriptions for the preferred oral anti-staphylococcal antibiotic, dicloxacillin. Repeat observations within a 12-month period were excluded prior to the calculation of age and gender standardised incidence rates per 100,000 person-years. We included 108,758 specimens, of which 42,778 (39%) yielded S. aureus. The annual incidence rate of specimens doubled during the study period, reaching 2,399 in 2008. The overall rate of S. aureus isolates increased 2-fold to a stable rate at about 850, but for isolates from children and for impetigo specimens, the increase was steeper, with a peak in 2002. A total of 156,462 dicloxacillin prescriptions had been redeemed and the annual prescription rate increased 2.5-fold, peaking at 3,714 in 2007. In conclusion, the annual rates of specimens, S. aureus infections and dicloxacillin prescriptions more than doubled in primary healthcare during the 12-year study period. A major impetigo epidemic and calls for antibiotic stewardship with increased utilisation of specimens were contributing factors.

Changing epidemiology of methicillin-resistant Staphylococcus aureus in Iceland from 2000 to 2008: a challenge to current guidelines

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is continuously changing. Iceland has a low incidence of MRSA. A "search and destroy" policy (screening patients with defined risk factors and attempting eradication in carriers) has been implemented since 1991. Clinical and microbiological data of all MRSA patients from the years 2000 to 2008 were collected prospectively. Isolates were characterized by pulsed-field gel electrophoresis (PFGE), sequencing of the repeat region of the Staphylococcus protein A gene (spa typing), staphylococcal cassette chromosome mec (SCCmec) typing, and screening for the Panton-Valentine leukocidin (PVL) gene. Two hundred twenty-six infected (60%) or colonized (40%) individuals were detected (annual incidence 2.5 to 16/100,000). From 2000 to 2003, two health care-associated outbreaks dominated (spa types t037 and t2802), which were successfully controlled with extensive infection control measures. After 2004, an increasing number of community-associated (CA) cases without relation to the health care system occurred. A great variety of clones (40 PFGE types and 49 spa types) were found, reflecting an influx of MRSA from abroad. The USA300 and Southwest Pacific (SWP) clones were common. SCCmec type IV was most common (72%), and 38% of the isolates were PVL positive. The incidence of MRSA in Iceland has increased since 1999 but remains low and has been stable in the last years. The search and destroy policy was effective to control MRSA in the health care setting. However, MRSA in Iceland is now shifting into the community, challenging the current Icelandic guidelines, which are tailored to the health care system.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Imported methicillin-resistant Staphylococcus aureus, Sweden

Knowledge of different risks for infection will improve control measures.

Countries such as Sweden that have a low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) offer the opportunity to discern and study transmission of imported cases of MRSA. We analyzed 444 imported cases of MRSA acquisition reported in Sweden during 2000–2003. Risk for MRSA in returning travelers ranged from 0.1 (95% confidence interval [CI] 0.01–0.4) per 1 million travelers to Nordic countries to 59.4 (95% CI 44.5–79.3) per 1 million travelers to North Africa and the Middle East. Most imported cases (246, 55%) were healthcare acquired, but regions with the highest risk for MRSA in travelers showed a correlation with community acquisition (r = 0.81, p = 0.001). Characteristic differences in MRSA strains acquired were dependent on the region from which they originated and whether they were community or healthcare acquired. Knowledge of differences in transmission of MRSA may improve control measures against imported cases.

Patient referral patterns and the spread of hospital-acquired infections through national health care networks

Rates of hospital-acquired infections, such as methicillin-resistant Staphylococcus aureus (MRSA), are increasingly used as quality indicators for hospital hygiene. Alternatively, these rates may vary between hospitals, because hospitals differ in admission and referral of potentially colonized patients. We assessed if different referral patterns between hospitals in health care networks can influence rates of hospital-acquired infections like MRSA. We used the Dutch medical registration of 2004 to measure the connectedness between hospitals. This allowed us to reconstruct the network of hospitals in the Netherlands. We used mathematical models to assess the effect of different patient referral patterns on the potential spread of hospital-acquired infections between hospitals, and between categories of hospitals (University medical centers, top clinical hospitals and general hospitals). University hospitals have a higher number of shared patients than teaching or general hospitals, and are therefore more likely to be among the first to receive colonized patients. Moreover, as the network is directional towards university hospitals, they have a higher prevalence, even when infection control measures are equally effective in all hospitals. Patient referral patterns have a profound effect on the spread of health care-associated infections like hospital-acquired MRSA. The MRSA prevalence therefore differs between hospitals with the position of each hospital within the health care network. Any comparison of MRSA rates between hospitals, as a benchmark for hospital hygiene, should therefore take the position of a hospital within the network into account.

The prevalence of hospital acquired infections is widely believed to reflect the quality of health care in individual hospitals, and is therefore often used as a benchmark. Intuitively, the idea is that infections spread more easily in hospitals with a poor quality of health care. This assumes that the rate at which admitted patients introduce new infections is the same for all hospitals. In this article, we show that this assumption is unlikely to be correct. Using national data on patient admissions, we are able to reconstruct the entire hospital network consisting of patients referred between hospitals. This network reveals that university hospitals admit more patients that recently stayed in other hospitals. Consequently, they are more likely to admit patients that still carry pathogens acquired during their previous hospital stay. Therefore, the prevalence of infections does not only reflect the quality of health care but also the connectedness to hospitals from which patients are referred. This phenomenon is missed at the single hospital level; our study is the first to address the connectedness between hospitals in explaining the prevalence of hospital acquired infections. Our findings imply that interventions should focus on hospitals that are central in the network of patient referrals.

Nasal colonization of humans with methicillin-resistant Staphylococcus aureus (MRSA) CC398 with and without exposure to pigs

BACKGROUND

Studies in several European countries and in North America revealed a frequent nasal colonization of livestock with MRSA CC398 and also in humans with direct professional exposure to colonized animals. The study presented here addresses the question of further transmission to non exposed humans.

METHODS

After selecting 47 farms with colonized pigs in different regions of Germany we sampled the nares of 113 humans working daily with pigs and of their 116 non exposed family members. The same was performed in 18 veterinarians attending pig farms and in 44 of their non exposed family members. For investigating transmission beyond families we samples the nares of 462 pupils attending a secondary school in a high density pig farming area. MRSA were detected by direct culture on selective agar. The isolates were typed by means of spa-sequence typing and classification of SCCmec elements. For attribution of spa sequence types to clonal lineages as defined by multi locus sequence typing we used the BURP algorithm. Antibiotic susceptibility testing was performed by microbroth dilution assay.

RESULTS

At the farms investigated 86% of humans exposed and only 4.3% of their family members were found to carry MRSA exhibiting spa-types corresponding to clonal complex CC398. Nasal colonization was also found in 45% of veterinarians caring for pig farms and in 9% of their non exposed family members. Multivariate analysis revealed that antibiotic usage prior to sampling beard no risk with respect to colonization. From 462 pupils only 3 were found colonized, all 3 were living on pig farms.

CONCLUSION

These results indicate that so far the dissemination of MRSA CC398 to non exposed humans is infrequent and probably does not reach beyond familial communities.

Evaluating the usefulness of spa typing, in comparison with pulsed-field gel electrophoresis, for epidemiological typing of methicillin-resistant Staphylococcus aureus in a low-prevalence region in Sweden 2000-2004

The usefulness of spa typing was evaluated in relation to pulsed-field gel electrophoresis (PFGE), as a tool for epidemiological typing of methicillin-resistant Staphylococcus aureus (MRSA) in a low-prevalence region in southern Sweden. Bacterial isolates from 216 MRSA cases, newly identified in 2000-2004, were studied. The isolates were obtained from infected patients (31%), and from colonized individuals found by screening (69%). In total, 49 spa types and 73 PFGE patterns were identified. The discriminatory power of spa typing was lower (94.9 +/- 1.8%) than that of PFGE (97.3 +/- 1.2%). For two spa types (t002 and t008) the Panton-Valentine leukocidin results added useful discriminatory information. The most common spa types were t044 (n = 31; four PFGE patterns), t002 (n = 24; 10 PFGE patterns), t067 (n = 12; four PFGE patterns), t050 (n = 12; one PFGE pattern), and t324 (n = 11; one PFGE pattern). Epidemiological investigations identified 91 single cases and 39 transmission chains, each involving two to 13 cases. All the transmission chains were held together both by spa and PFGE typing. Among the 91 single-case isolates, 33 spa types and 50 PFGE patterns were unique (matchless) at the time of identification. The low prevalence of MRSA, the low number of outbreaks, and the wide spectrum of strains due to frequent acquisitions abroad (49% of the cases), makes spa typing a useful complement to epidemiological investigations in our setting. However, we still recommend the continued use of PFGE for further discrimination of isolates with identical spa types when epidemiological data can not exclude possible transmission.

Methicillin-susceptible Staphylococcus aureus in skin and soft tissue infections, Northern Italy

Summary statement: A community outbreak with intrafamilial skin infections was associated with an MSSA clone.

During February 2004–September 2006, familial clusters and sporadic cases of Staphylococcus aureus skin and soft tissue infections were observed in a suburban area near Milan in northern Italy. Molecular typing of the isolates showed an epidemic methicillin-susceptible S. aureus (MSSA) strain, spa type 005 and sequence type 22 that harbored Panton-Valentine leukocidin (PVL) genes. The first case-patients were neonates or mothers who had recently delivered in the local hospital. Examination of the medical records showed a cluster of postpartum mastitis and neonatal skin infections antedating the emergence of infections in the community. Nasal swabs of neonates, mothers, and hospital staff were positive for the epidemic MSSA. Hospital circulation of the strain was interrupted by implementation of infection control measures, although infections continued to occur in the community. The PVL-positive MSSA strain resembles typical community-acquired methicillin-resistant S. aureus in its ability to cause prolonged community and hospital outbreaks of skin infections.

Comparative genomic analysis of European and Middle Eastern community-associated methicillin-resistant Staphylococcus aureus (CC80:ST80-IV) isolates by high-density microarray

Infections as a result of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are an issue of increasing global healthcare concern. In Europe, this principally involves strains of multi-locus sequence type clonal complex 80 sequence type 80 with methicillin resistance in a staphylococcal chromosomal cassette (SCCmec) type IV arrangement (CC80:ST80-IV). As with other CA-MRSA strains, CC80:ST80-IV isolates tend to appear uniform when analysed by common molecular typing methods (e.g. pulsed field gel electrophoresis, multi-locus sequence type, SCCmec). To explore whether DNA sequence-based differences exist, we compared the genetic composition of six CC80:ST80-IV isolates of diverse chronological and geographic origin (i.e. Denmark and the Middle East) using an Affymetrix high-density microarray that was previously used to analyse CA-MRSA USA300 isolates. The results revealed a high degree of homology despite the diversity in isolation date and origin, with isolate differences primarily in conserved hypothetical open reading frames and intergenic sequences, but also including regions of known function. This included the confirmed loss of SCCmec recombinase genes in two Danish isolates representing potentially new SCCmec types. Microarray analysis grouped the six isolates into three relatedness pairs, also identified by pulsed field gel electrophoresis, which were consistent with both the clinical and molecular data.

Laboratory tools and strategies for methicillin-resistant Staphylococcus aureus screening, surveillance and typing: state of the art and unmet needs

The public health burden caused by methicillin-resistant Staphylococcus aureus (MRSA) infections is now widely recognized, and is a cause of public alarm. Effective MRSA risk management in the healthcare system as well as in the community should rely on accurate detection of reservoirs and sources of transmission, as well as on close monitoring of the impact of interventions on disease incidence and bacterial dissemination. MRSA carrier screening and disease surveillance, coupled with molecular typing, are key information tools for integrated MRSA control and individual risk assessment. These tools should be tailored to the distinct needs of local interventions and national prevention programmes. Surveillance schemes should primarily inform local staff and serve as quality assurance about MRSA risk management. New technologies, including the use of selective culture media and real-time PCR assays, allow faster detection of MRSA carriers upon admission or during stay in healthcare institutions. More research is needed to ascertain their cost-effectiveness for MRSA control. Likewise, tremendous progress has been made concerning molecular typing methods, with optimization and standardization of sequence-based technologies offering broad applicability and high throughput. However, no single S. aureus typing method is yet providing fully reliable information within the range of discrimination needed for public health action. Further refinement of genotyping methods and international harmonization of surveillance and typing schemes must be achieved to facilitate global MRSA control.

Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus outbreak among healthcare workers in a long-term care facility

BACKGROUND

We investigated an outbreak of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections that occurred among healthcare workers (HCWs) but not among residents of a long-term care facility (LTCF).

METHODS

Cases of S. aureus infection were sought by reviewing the medical records of residents and HCWs. In order to identify risk factors for the development of an S. aureus infection, an unmatched case-control study was conducted. Cases were all HCWs with a clinically compatible S. aureus infection; controls were HCWs with no history of a clinically compatible S. aureus infection. Cases and controls were interviewed and anterior nasal swabs were collected.

RESULTS

Over a period of 14 months, a total of eight cases were identified among practice nurses, giving an attack rate of 10% for this category of profession. All isolates were identified as MRSA Panton-Valentine leukocidin (PVL)-producing SCCmec type IV. By multivariate analysis, working in a specific zone and being a practice nurse were found to be statistically significant risk factors for infection.

CONCLUSIONS

The current outbreak indicates that HCWs may serve as vehicles for the entry of PVL-positive MRSA strains from the community into LTCFs, and that deficient hygiene practices and unrecognized carriage may facilitate spread. Given the increasing prevalence of PVL-positive MRSA infections worldwide, guidelines for the eradication of PVL-positive MRSA carriage within closed communities should be established and efforts to obtain cultures from compatible infections should be made.

Emergence and characterization of community-associated methicillin-resistant Staphyloccocus aureus infections in Denmark, 1999 to 2006

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) infections has changed worldwide. From being strictly nosocomial, MRSA is now frequently found as a community-associated (CA) pathogen. Denmark has been a low-prevalence country for MRSA since the mid-1970s but has in recent years experienced an increasing number of CA-MRSA cases. The aim of this study was to describe the emergence of CA-MRSA infections in Denmark. All Danish MRSA specimens and corresponding clinical data from 1999 to 2006 were investigated. Isolates were analyzed by antibiotic resistance and molecular typing and were assigned to clonal complexes (CC). Clinical data were extracted from discharge summaries and general practitioners' notes, from which assessments of community association were made for all infected cases. CA-MRSA cases constituted 29.4% of all MRSA infections (n = 1,790) and an increasing proportion of the annual numbers of MRSA infections during the study period. CA-MRSA was associated with a young age, skin and soft tissue infections, and non-Danish origin. Transmission between household members was frequently reported. Molecular typing showed >60 circulating clones, where 89.4% of the isolates belonged to five CC (CC80, CC8, CC30, CC5, and CC22), 81.2% carried staphylococcal cassette chromosome mec IV, and 163/244 (69.4%) were positive for Panton-Valentine leukocidin. Clinical and microbiological characteristics indicated that import of MRSA occurs frequently. Resistance to > or =3 antibiotic classes was observed for 48.8% of the isolates. The emergence of CA-MRSA in Denmark was caused by diverse strains, both well-known and new CA-MRSA strains. The results suggest multiple introductions of MRSA as an important source for CA-MRSA infections in Denmark.

Is an increase of MRSA in Oslo, Norway, associated with changed infection control policy?

OBJECTIVES

The objective was to describe the prevalence of MRSA in Oslo, Norway, before and after introduction of a new National MRSA Control Guideline.

METHODS

From 1993 to 2006, we prospectively collected clinical and microbiological data on all MRSA cases in Oslo, Norway. Two MRSA guidelines; a strict Ullevål Standard MRSA Guideline and a less strict National MRSA Control Guideline were compared.

RESULTS

During 1993-2006, 358 MRSA cases were registered in Oslo; 43.9% detected in Ullevål University Hospital, 21.2% in nursing homes, and 18.7% in primary healthcare. One out of three (30.4%) were import-associated, and one out of ten (11.2%) were healthcare personnel. From 2004 on, a new National MRSA Control Guideline was introduced in primary healthcare, served by the community infection control. From 2004 on, there was a 4-6-fold increase of MRSA in primary healthcare (p = 0.038) and nursing homes (p = 0.005). Increase of MRSA cases at Ullevål (p < 0.001) was import-associated or from outbreaks in primary healthcare. There was no increase of internal spread in the hospital.

CONCLUSION

These data indicate that perhaps a less strict national MRSA infection control guideline in Norway may be associated with the 4-6-fold increase of MRSA cases in the community after 2003.

Epidemiology of European community-associated methicillin-resistant Staphylococcus aureus clonal complex 80 type IV strains isolated in Denmark from 1993 to 2004

In Europe, community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have been caused predominantly by isolates belonging to the "European CA-MRSA" clone (sequence type 80, staphylococcal cassette chromosome mec type IV). In this study, the epidemiology of European CA-MRSA was investigated on a nationwide scale, covering the period from 1993 to 2004. Denmark has been a low-prevalence country regarding MRSA since the mid-1970s but has experienced an increase in the number of new MRSA cases in recent years. Our results show that European CA-MRSA contributed to this increase. The isolates primarily caused skin and soft tissue infections (SSTIs) in patients outside hospitals, and transmission between household members was the predominant mode of spread. Although some of the isolates were found in hospitalized patients, nosocomial transmission seemed likely in only one instance, pointing to endogenous infections as an important factor. Compared to the CA-MRSA clone most common in the United States (USA300), the European CA-MRSA clone seems less well adapted to persist in hospital environments. Patients with a recent history of travel or family relation to the Mediterranean or Middle East were highly overrepresented. The epidemiological data indicated that the European CA-MRSA isolates were introduced into Denmark on multiple occasions, paralleled by an increasing level of genetic diversity of the isolates found during the study period. European CA-MRSA has previously been described as a rather uniform clone. However, we found pronounced, diverse pulsed-field gel electrophoresis subtypes, staphylococcal protein A gene (spa) types, and susceptibility patterns.

Allelic variation in genes encoding Panton–Valentine leukocidin from community-associated Staphylococcus aureus

Community-associated methicillin-resistant Staphylococcus aureus isolates characteristically contain the genes for Panton-Valentine leukocidin (PVL), which is a proposed virulence factor. To determine whether different alleles of the PVL genes lukS-PV and lukF-PV occur, and whether they are associated with specific genetic lineages of S. aureus, sequences from 28 S. aureus isolates, representing four different multilocus sequence types, and bacteriophages SLT and PVL were compared. Seven nucleotide polymorphisms were identified, which defined three groups of the lukS-PV and lukF-PV sequence. Only one polymorphism resulted in an amino-acid change. Bacteriophage SLT and isolates of bacteriophage type 80/81 contained the prototypic (founder) lukS-PV and lukF-PV sequence. The alleles were not lineage-specific.

Comparative genomics and DNA array-based genotyping of pandemic Staphylococcus aureus strains encoding Panton-Valentine leukocidin

Within the last few years, methicillin-resistant Staphylococcus aureus (MRSA) strains encoding Panton-Valentine leukocidin (PVL) have emerged and spread worldwide. This epidemic can be attributed to a small number of distinct clones. The present study used a novel assay, based on multiplex linear DNA amplification and subsequent microarray hybridisation, to simultaneously detect all relevant exotoxins, antimicrobial resistance determinants and the allelic variants of agr. The genes of the staphylococcal exotoxin-like (set) locus were also included for typing purposes. This assay, together with multilocus sequence typing (MLST) and spa typing, was applied to 56 clinical isolates and reference strains representing all major pandemic PVL-MRSA lineages, as well as to phylogenetically-related strains and putative ancestors. Array hybridisation results allowed the assignment of isolates to clonal groups, which were in accordance with MLST and spa typing data. Ten distinct clonal groups of PVL-MRSA (ST1, ST5, ST8, ST22, ST30, ST59/359, ST80/583, ST88, ST93 and ST152), including 12 MLST types, were identified and analysed with regard to resistance determinants and genes coding for exotoxins. The array hybridisation data confirmed that pandemic PVL-positive strains originate from very diverse genetic backgrounds, and provided insights into the evolution of some lineages. The DNA microarray technique provides a valuable epidemiological tool for the detailed characterisation of clinical isolates and comparison of strains at a global level.

Molecular epidemiology and household transmission of community-associated methicillin-resistant Staphylococcus aureus in Hong Kong

This study evaluated the clinical and epidemiologic features of individuals with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Hong Kong from January 2004 through December 2005. Twenty-four episodes of skin and soft tissue infections and 1 episode of meningitis due to CA-MRSA were identified. CA-MRSA infections or carriage was found in 6 (13%) of 46 household contacts. A total of 29 isolates were analyzed by the Staphylococcus cassette chromosome mec (SCCmec) typing, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing. In addition, polymerase chain reaction detection of the genes encoding Panton-Valentine leukocidin was also carried out. It was observed that 24 had SCCmec IV/IVA and 5 had SCCmec V, and 23 were pvl positive. PFGE analysis clustered all except 1 isolate into 3 pulsed-field types (PFTs), HKU100 through HKU300. The HKU100 isolates had genotype ST30-IV identical to the Southwest Pacific clone. The HKU200 isolates belonged to ST59-V and were multiresistant, including an ermB-mediated macrolide resistance trait, which is characteristic of the predominant CA-MRSA clone in Taiwan. The HKU300 isolates had unique features (ST8, Panton-Valentine leukocidin negative, and SCCmec IVA) typical of CA-MRSA in Japan. In conclusion, CA-MRSA has a propensity to spread within families. Our findings showed that CA-MRSA strains in Hong Kong have diverse genetic backgrounds.

Multiple cases of familial transmission of community-acquired methicillin-resistant Staphylococcus aureus

The worldwide emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) can have severe public health implications. Familial transmissions of CA-MRSA in The Netherlands were investigated. Among the families studied, two clusters of CA-MRSA could be identified. This report demonstrates that family members can serve as reservoirs of CA-MRSA which may become a serious problem in containing the spread of MRSA.

Microarray-based characterisation of a Panton-Valentine leukocidin-positive community-acquired strain of methicillin-resistant Staphylococcus aureus

Recent years have witnessed the emergence of novel methicillin-resistant Staphylococcus aureus (MRSA) strains that produce the potent toxin Panton-Valentine leukocidin (PVL). PVL-positive strains can cause complicated skin infections or necrotising pneumonia with high mortality, and these strains have the potential for epidemic spread in the community. In 2004-2005, two case clusters and two isolated cases were observed in eastern Saxony and southern Brandenburg. These were the first known infections with PVL-positive community-acquired MRSA (caMRSA) in this part of Germany. The isolates belonged to agr type III, spa type 44 or spa type 131, and showed a SmaI macrorestriction pattern that corresponded to caMRSA of clonal group ST80. The isolates were susceptible to levofloxacin, macrolides, clindamycin, gentamicin and vancomycin. Most isolates showed resistance to tetracycline and fusidic acid because of the presence of the tetK and far1 genes. A novel plasmid (designated pUB102) harbouring far1, tetK and blaZ was characterised and partially sequenced. Microarray analysis revealed that the caMRSA isolates harboured genes encoding several bi-component toxins (lukF/S-PVL, lukD/E, lukS/F plus hlgA, and another putative leukocidin homologue). Neither tst1 nor genes for enterotoxins A-Y were detected, but the isolates harboured several staphylococcal enterotoxin-like toxin genes (set genes), as well as genes encoding an epidermal cell differentiation inhibitor (edinB) and exfoliative toxin D (etD). Comparative analysis of other isolates from Australia, Germany, Switzerland and the UK showed that these isolates were representative of a widespread clone of caMRSA.

Community-associated Methicillin-resistant Staphylococcus aureus: Overview and Local Situation

Introduction: Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged worldwide. In contrast to healthcare-associated MRSA (HA-MRSA), CA-MRSA isolates are usually susceptible to multiple non-beta-lactam antibiotics and cause a distinct spectrum of infections in epidemiologically disparate populations – in particular, cutaneous abscesses, necrotising fasciitis and necrotising pneumonia. They arise from a broader genetic background, and possess differing virulence genes. We aim to describe the distribution of different molecular subtypes of CA-MRSA among various regions and discuss briefly the implications of CA-MRSA from a local perspective. Methods: Literature review of articles on CA-MRSA, focusing mainly on reports where the genetic background of isolates had been analysed using multi-locus sequence typing (MLST). Singapore data were obtained from the local CA-MRSA database. Results: MLST analysis demonstrated the presence of epidemic subtypes of CA-MRSA within most geographic areas. In parts of the United States, community MRSA infections currently exceed those caused by their methicillin-susceptible counterparts. In Singapore, CA-MRSA infections are increasing, predominantly as a result of the spread of ST30 clones. Conclusion: Available evidence suggests that the emergence of MRSA from the community is not going to be a transient phenomenon. Local guidelines for dealing with this phenomenon at both therapeutic and preventive levels are needed prior to the potential development of a situation mirroring that of meso-endemic HA-MRSA in local hospitals or CA-MRSA epidemics in parts of USA. Key words: Bacterial typing, Epidemic, Epidemiology, Infection control

Control of a methicillin-resistant Staphylococcus aureus (MRSA) outbreak in a day-care institution

This article describes an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) in two institutions for multi-handicapped children in Copenhagen. The aim of the study was to determine whether it was possible to eradicate MRSA in a setting with multi-handicapped children and staff where there was a high degree of physical interaction. This was a prospective interventional uncontrolled cohort study that took place from January 2003 to March 2005. All individuals in close contact with the two institutions and/or in close contact with an MRSA-colonized subject from the outbreak were included in the study: 38 children, 60 staff members and 12 close relatives of colonized subjects. Infection control measures included screening all individuals. When MRSA infection or colonization was found, an attempt was made to eradicate MRSA, staff education was undertaken and attempts were made to determine the route of transmission. Eleven individuals were found to be positive for MRSA (10.0%). All isolates were identical by pulsed-field gel electrophoresis and harboured the staphylococcal cassette chromosome mec (SCCmec) type IV. All colonized and infected individuals were associated with a single room in one of the institutions. MRSA was eradicated from all the colonized and infected subjects. This study shows that it is possible to control an MRSA outbreak in institutions for multi-handicapped children where there is a high degree of physical contact.

The throat: an important site for MRSA colonization

In order to evaluate the value of bacterial cultures taken from the throat, 266 patients with MRSA were retrospectively assessed. At the time when MRSA was first detected in the patient, the most frequent sites positive for MRSA were a skin lesion (110 patients, 41%), the anterior nares (109 patients, 41%), and the throat (102 patients, 38%). In 26%, 17%, and 17% of the patients, a skin lesion, the anterior nares, and the throat, respectively, were the only site where MRSA was seen. In 123 patients cultured for MRSA because of a close contact with an already known MRSA patient, 65 patients (53%) were positive for MRSA in their throat and in 40 patients (33%), throat was the only sample site with MRSA at the time when the patient was found to be MRSA positive. 146 of the 266 patients (55%) were colonized with MRSA in the throat any time throughout the period they were MRSA positive. We conclude that throat is an important reservoir for MRSA and that samples taken from the throat should be included in screening patients for MRSA.