Changing epidemiology of methicillin-resistant Staphylococcus aureus in Finland

Bacterial extracellular vesicle-coated multi-antigenic nanovaccines protect against drug-resistant Staphylococcus aureus infection by modulating antigen processing and presentation pathways

Background: Vaccination provides an alternative to antibiotics in addressing drug-resistant Staphylococcus aureus (S. aureus) infection. However, vaccine potency is often limited by a lack of antigenic breadth and a demand on the generation of antibody responses alone.

Methods: In this study, bacterial extracellular vesicles (EVs) coating indocyanine green (ICG)-loaded magnetic mesoporous silica nanoparticles (MSN) were constructed as multi-antigenic vaccines (EV/ICG/MSN) with the ability to modulate antigen presentation pathways in dendritic cells (DCs) to induce cellular immune responses.

Results: Exposing the EV/ICG/MSNs to a laser could promote DC maturation and enhance the proteasome-dependent antigen presentation pathway by facilitating endolysosomal escape, improving proteasome activity, and elevating MHC-I expression. Immunization by EV/ICG/MSNs with laser irradiation in vivo triggered improved CD8⁺ T cell responses while maintaining CD4⁺ T cell responses and humoral immunity. In addition, in vivo tracking data revealed that the vaccine could be efficiently transported from the injection site into lymph nodes. Skin infection experiments showed that the vaccine not only prevented and treated superficial infection but also decreased bacterial invasiveness, thus strongly suggesting that EV/ICG/MSNs were effective in preventing complications resulting from the introduction of S. aureus infections.

Conclusion: This multi-antigenic nanovaccine-based modulation of antigen presentation pathways provides an effective strategy against drug-resistant S. aureus infection.

Changing epidemiology of methicillin-resistant Staphylococcus aureus in a low endemicity area-new challenges for MRSA control

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) has increased sharply in Hospital District of Southwest Finland (HD). To understand reasons behind this, a retrospective, population-based study covering 10 years was conducted. All new 983 MRSA cases in HD from January 2007 to December 2016 were analysed. Several data sources were used to gather background information on the cases. MRSA cases were classified as healthcare-associated (HA-MRSA), community-associated (CA-MRSA), and livestock contact was determined (livestock-associated MRSA, LA-MRSA). Spa typing was performed to all available strains. The incidence of MRSA doubled from 12.4 to 24.9 cases/100000 persons/year. The proportion of clinical infections increased from 25 to 32% in the 5-year periods, respectively, (p < 0.05). The median age decreased from 61 years in 2007 to 30 years in 2016. HA-MRSA accounted for 68% of all cases, of which 32% associated with 26 healthcare outbreaks. The proportion of CA-MRSA cases increased from 13% in 2007 to 43% in 2016. Of CA-MRSA cases, 43% were among family clusters, 32% in immigrants and 4% were LA-MRSA. The Gini-Simpson diversity index for spa types increased from 0.86 to 0.95 from the first to the second 5-year period. The proportion of a predominant strain t172 decreased from 43% in 2009 to 7% in 2016. The rise in the proportion of CA-MRSA, the switch to younger age groups, the complexity of possible transmission routes and the growing spa-type diversity characterize our current MRSA landscape. This creates challenges for targeted infection control measures, demanding further studies.

Methicillin-resistant Staphylococcus aureus epidemic restricted to one health district in Finland: a population-based descriptive study in Pirkanmaa, Finland, years 2001-2011

BACKGROUND

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) has been low in the Scandinavian countries, including Finland.

METHODS

We report a population-based, prospective survey of an exceptionally large ongoing MRSA epidemic in a Finnish health district (HD), Pirkanmaa HD, during 2001-2011 caused by 1 strain, spa t067 (FIN-16).

RESULTS

The first FIN-16 case in the HD was identified in 2000. Ten years later, 2447 carriers had been found in 95 different institutions. MRSA in carriers was mostly health care-associated (98%). The epidemic emerged in long-term care facilities and gradually spread to acute hospitals. The majority of carriers were elderly people (median age 78 y). Fifty-two percent of new carriers had an infection with MRSA at the time of detection.

CONCLUSIONS

The incidence of MRSA in Pirkanmaa HD is substantially higher than the incidence for all of Finland. Temporary projects to control MRSA have not proved sufficient to contain this large epidemic.

Staphylococcus aureus: a community pathogen

Staphylococcus aureus is a common human pathogen. S aureus infections most commonly clinically manifest as skin infections. There has been much interest in S aureus infections in the community over the past decade because of the rise of community-associated methicillin-resistant S aureus (CA-MRSA) infections, which have emerged globally over a relatively short period of time. In contrast to health care-associated methicillin resistant S aureus (HA-MRSA), circulating strains of CA-MRSA have characteristic pathogenesis, strain characteristics, epidemiology, and clinical manifestations that are distinct from HA-MRSA. In fact, CA-MRSA probably behaves more like community-associated methicillin-sensitive S aureus (MSSA). This article reviews current knowledge of the epidemiology and clinical manifestations of community-associated S aureus and CA-MRSA infections.

Promoting hand hygiene and prudent use of antimicrobials in long-term care facilities

A multidisciplinary team visited all long-term care facilities (n = 123) for elderly persons in the Central Finland health care district (population, 265,000) during 2004-2005. Use of alcohol-based hand rubs and ongoing systematic antimicrobials were assessed. Thereafter, regional guidelines for prudent use of antimicrobials were published. One year after the visits, a significant increase in the mean amount of alcohol-based hand rubs used was detected while usage of antimicrobials for the prevention of urinary tract reinfections had decreased.

Mortality after infection with methicillin-resistant Staphylococcus aureus (MRSA) diagnosed in the community

BACKGROUND

Outbreak reports suggest that community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections can be life-threatening. We conducted a population based cohort study to assess the magnitude of mortality associated with MRSA infections diagnosed in the community.

METHODS

We used the United Kingdom's General Practice Research Database (GPRD) to form a cohort of all patients with MRSA diagnosed in the community from 2001 through 2004 and up to ten patients without an MRSA diagnosis. The latter were frequency-matched with the MRSA patients on age, GPRD practice and diagnosis date. All patients were older than 18 years, had no hospitalization in the 2 years prior to cohort entry and medical history information of at least 2 years prior to cohort entry. The cohort was followed up for 1 year and all deaths and hospitalizations were identified. Hazard ratios of all-cause mortality were estimated using the Cox proportional hazards model adjusted for patient characteristics.

RESULTS

The cohort included 1439 patients diagnosed with MRSA and 14,090 patients with no MRSA diagnosis. Mean age at cohort entry was 70 years in both groups, while co-morbid conditions were more prevalent in the patients with MRSA. Within 1 year, 21.8% of MRSA patients died as compared with 5.0% of non-MRSA patients. The risk of death was increased in patients diagnosed with MRSA in the community (adjusted hazard ratio 4.1; 95% confidence interval: 3.5-4.7).

CONCLUSION

MRSA infections diagnosed in the community are associated with significant mortality in the year after diagnosis.

Evaluation of phenotypic and molecular methods for screening and detection of methicillin-resistant Staphylococcus aureus

An in-house PCR was compared with the GenoType MRSA and the MRSA EVIGENE tests, both of which corresponded 100% with the results of in-house PCR. The cefoxitin disk diffusion method was superior to both the oxacillin disk diffusion and minimum inhibitory concentration tests for predicting the mecA status.

Nationwide trends in molecular epidemiology of methicillin-resistant Staphylococcus aureus, Finland, 1997-2004

Background

In Finland, the annual number of MRSA notifications to the National Infectious Disease Register (NIDR) has constantly increased since 1995, and molecular typing has revealed numerous outbreak isolates of MRSA. We analyzed the data on MRSA notifications of the NIDR, and MRSA isolates were identified mainly by pulsed-field gel electrophoresis (PFGE) at the National Reference Laboratory (NRL) in Finland during 1997–2004. One isolate representative of each major PFGE type was further characterized by multilocus sequence (MLST)-, staphylococcal cassette chromosome mec (SCCmec)-, and Panton-Valentine leukocidin (PVL)-typing.

Results

The annual number of MRSA notifications to the NIDR rose over ten-fold, from 120 in 1997 to 1458 in 2004, and the proportion of MRSA among S. aureus blood isolates tripled, from <1% during 1997–2003 to 2.8% in 2004. During the same period of time, 253 different strains among 4091 MRSA isolates were identified by PFGE: 215 were sporadic and 38 outbreak/epidemic strains, including 24 new strains. Two epidemic strains resembling internationally recognized MRSA clones accounted for most of the increase: FIN-16 (ST125:IA) from <1% in 1997 to 25% in 2004, and FIN-21 (ST228:I) from 6% in 2002 to 28% in 2004. Half of the ten most common strains carried SCCmec IV or V.

Conclusion

The predominant MRSA strains seem to change over time, which encourages us to continue implementing active control measures with each new MRSA case.

National guidelines for the control and prevention of methicillin-resistant Staphylococcus aureus--what do they tell us?

Guidelines to control and prevent methicillin-resistant Staphylococcus aureus (MRSA) infection are available in many countries. Infection control and prevention teams determine local strategies using such national guidelines, but not all guidelines involve a rigorous assessment of the literature to determine the strength of the recommendations. Available guidelines drafted by national agencies or prominent professional organisations in Germany, New Zealand, North America, The Netherlands, Ireland and the UK were reviewed. Significant literature reviews were a component of guidelines from the UK and North America. Recommendations were not graded on the strength of the evidence in guidelines from New Zealand and The Netherlands. The Netherlands, a country with a very low prevalence of MRSA, had the simplest set of guidelines. Few of the recommendations in any of the guidelines achieved the highest grading, i.e., based on well-designed, experimental, clinical or epidemiological studies, even though the logic of the proposed measures is clear. The onset of community-acquired MRSA is reflected in the recent publication of guidelines from North America. New developments, such as rapid testing and mathematical modelling, are of importance in helping to control MRSA in settings of both low and high endemicity. National guidelines are increasingly evidence-based, although good scientific studies concerning some aspects of MRSA control are lacking. However, general principles, e.g., early detection and isolation, are recommended by all guidelines. There is still a role for consensus and the opinion of experts in devising national guidelines.

Staphylococcus aureus colonization among nursing home residents in a large Finnish nursing home

We studied colonization with methicillin-resistant and -sensitive Staphylococcus aureus (MRSA, MSSA) in the second largest nursing home in Finland, in which the residents volunteered had their nostrils, throats, perineums, skin lesions, and catheter exit sites swabbed, and catheter urines cultured. The specimens were cultured onto non-selective and selective agar, with or without enrichment in salt-containing trypticase soy broth (TSB). S. aureus was identified by routine methods, methicillin resistance was detected by oxacillin and cefoxitin disk diffusion and MIC E-tests, and GenoType MRSA -test was used for mecA gene confirmation. A total of 663 cultures were obtained from 213 residents. Of those, 165 specimens (25%) from 94 residents (44%) were positive for S. aureus, and 3 specimens (0.4%) from 2 (0.9%) residents were positive for MRSA. Of the 165 S. aureus isolates, 31 (19%) from 25 (27%) residents were found only from sites other than nostrils (30 MSSA and 1 MRSA). TSB enrichment detected additional 33 (5%) S. aureus isolates (32 MSSA and 1 MRSA), resulting in 8 (5%) additional residents. None of the MRSA strains would have been found if only nostrils and throat had been screened, and no enrichment broth had been used.

[Positive screening for MRSA--clinical consequences?]

BACKGROUND

The worldwide rise of MRSA is equivalent to an increase of nasal colonization with MRSA. The objectives of this study were to investigate the rate of occult nasal MRSA colonization in trauma patients, to elucidate the role of MRSA carriers for endogenous infection (nose --> wound) and to check the efficiency of mupirocin therapy.

PATIENTS AND METHODS

A total of 643 consecutive trauma patients underwent MRSA screening (nasal swabs) on admission. At the same time all MRSA wound infections were registered and all isolates were analysed with PFGE (pulsed-field gel electrophoresis) to detect cross-infection between individuals.

RESULTS

In 13 patients (2.0%) we found MRSA in the nose and limited isolation as well as therapy with mupirocin were performed. No endogenous transmission of MRSA from the nose to the wound could be seen, and no cross-infection to other patients could be detected.

CONCLUSION

Our findings suggest that in our patients with nasal colonization the risk of intra- and interindividual transmission of MRSA is very small. Therefore, in trauma patients screening on admission does not seem to be absolutely necessary either for clinical or for epidemiological reasons.

Methicillin-resistant Staphylococcus aureus on orthopaedic wards: incidence, spread, mortality, cost and control

We examined the rates of infection and colonisation by methicillin-resistant Staphylococcus aureus (MRSA) between January 2003 and May 2004 in order to assess the impact of the introduction of an MRSA policy in October 2003, which required all admissions to be screened. Emergency admissions were treated prophylactically and elective beds ring-fenced. A total of 5,594 admissions were cross-referenced with 22,810 microbiology results. The morbidity, mortality and cost of managing MRSA-carrying patients, with a proximal fracture of the femur were compared, in relation to age, gender, American Society of Anaesthesiologists grade and residential status, with a group of matched controls who were MRSA-negative. In 2004, we screened 1795 of 1,796 elective admissions and MRSA was found in 23 (1.3%). We also screened 1,122 of 1,447 trauma admissions and 43 (3.8%) were carrying MRSA. All ten ward transfers were screened and four (40%) were carriers (all p < 0.001). The incidence of MRSA in trauma patients increased by 2.6% per week of inpatient stay (r = 0.97, p < 0.001). MRSA developed in 2.9% of trauma and 0.2% of elective patients during that admission (p < 0.001). The implementation of the MRSA policy reduced the incidence of MRSA infection by 56% in trauma patients (1.57% in 2003 (17 of 1,084) to 0.69% in 2004 (10 of 1,447), p = 0.035). Infection with MRSA in elective patients was reduced by 70% (0.56% in 2003 (7 of 1,257) to 0.17% in 2004 (3 of 1,806), p = 0.06). The cost of preventing one MRSA infection was 3,200 pounds. Although colonisation by MRSA did not affect the mortality rate, infection by MRSA more than doubled it. Patients with proximal fractures of the femur infected with MRSA remained in hospital for 50 extra days, had 19 more days of vancomycin treatment and 26 more days of vacuum-assisted closure therapy than the matched controls. These additional costs equated to 13,972 pounds per patient. From this experience we have been able to describe the epidemiology of MRSA, assess the impact of infection-control measures on MRSA infection rates and determine the morbidity, mortality and economic cost of MRSA carriage on trauma and elective orthopaedic wards.

Guidelines for the control and prevention of meticillin-resistant Staphylococcus aureus (MRSA) in healthcare facilities

Meticillin-resistant Staphylococcus aureus (MRSA) remains endemic in many UK hospitals. Specific guidelines for control and prevention are justified because MRSA causes serious illness and results in significant additional healthcare costs. Guidelines were drafted by a multi-disciplinary group and these have been finalised following extensive consultation. The recommendations have been graded according to the strength of evidence. Surveillance of MRSA should be undertaken in a systematic way and should be fed back routinely to healthcare staff. The inappropriate or unnecessary use of antibiotics should be avoided, and this will also reduce the likelihood of the emergence and spread of strains with reduced susceptibility to glycopeptides, i.e. vancomycin-intermediate S. aureus/glycopeptide-intermediate S. aureus (VISA/GISA) and vancomycin-resistant S. aureus (VRSA). Screening for MRSA carriage in selected patients and clinical areas should be performed according to locally agreed criteria based upon assessment of the risks and consequences of transmission and infection. Nasal and skin decolonization should be considered in certain categories of patients. The general principles of infection control should be adopted for patients with MRSA, including patient isolation and the appropriate cleaning and decontamination of clinical areas. Inadequate staffing, especially amongst nurses, contributes to the increased prevalence of MRSA. Laboratories should notify the relevant national authorities if VISA/GISA or VRSA isolates are identified.

Epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in Sweden 2000-2003, increasing incidence and regional differences

Background

The occurrence of methicillin-resistant Staphylococcus aureus (MRSA) has gradually become more frequent in most countries of the world. Sweden has remained one of few exceptions to the high occurrence of MRSA in many other countries. During the late 1990s, Sweden experienced a large health-care associated outbreak which with resolute efforts was overcome. Subsequently, MRSA was made a notifiable diagnosis in Sweden in 2000.

Methods

From the start of being a notifiable disease in January 2000, the Swedish Institute for Infectious Disease Control (SMI) initiated an active surveillance of MRSA.

Results

The number of reported MRSA-cases in Sweden increased from 325 cases in 2000 to 544 in 2003, corresponding to an overall increase in incidence from 3.7 to 6.1 per 100000 inhabitants. Twenty five per cent of the cases were infected abroad. The domestic cases were predominantly found through cultures taken on clinical indication and the cases infected abroad through screening. There were considerable regional differences in MRSA-incidence and age-distribution of cases.

Conclusion

The MRSA incidence in Sweden increased over the years 2000–2003. Sweden now poises on the rim of the same development that was seen in the United Kingdom some ten years ago. A quarter of the cases were infected abroad, reflecting that international transmission is now increasingly important in a low-endemic setting. To remain in this favourable situation, stepped up measures will be needed, to identify imported cases, to control domestic outbreaks and to prevent transmission within the health-care sector.

Comparison of genotypes of methicillin-resistant and methicillin-sensitive Staphylococcus aureus in Finland

The frequency of horizontal transfer of the staphylococcal cassette chromosome mec to methicillin-susceptible Staphylococcus aureus is unknown. In order to gain more information regarding this frequency in Finland, the genotypes of 299 clinical methicillin-sensitive Staphylococcus aureus isolates were compared to representatives of 24 epidemic methicillin-resistant Staphylococcus aureus genotypes. Sixty-eight percent of the methicillin-sensitive isolates had a genotype similar to eight of the epidemic methicillin-resistant strains. The remaining isolates (32%) showed 22 different genotypes. The results indicate that, in Finland, several methicillin-sensitive Staphylococcus aureus genotypes may have acquired the staphylococcal cassette chromosome mec.