Monitoring the spread of meticillin-resistant Staphylococcus aureus in The Netherlands from a reference laboratory perspective.

BACKGROUND: In The Netherlands, efforts to control meticillin-resistant Staphylococcus aureus (MRSA) in hospitals have been largely successful due to stringent screening of patients on admission and isolation of those that fall into defined risk categories. However, Dutch hospitals are not free of MRSA, and a considerable number of cases are found that do not belong to any of the risk categories. Some of these may be due to undetected nosocomial transmission, whereas others may be introduced from unknown reservoirs. AIM: Identifying multi-institutional clusters of MRSA isolates to estimate the contribution of potential unobserved reservoirs in The Netherlands. METHODS: We applied a clustering algorithm that combines time, place, and genetics to routine data available for all MRSA isolates submitted to the Dutch Staphylococcal Reference Laboratory between 2008 and 2011 in order to map the geo-temporal distribution of MRSA clonal lineages in The Netherlands. FINDINGS: Of the 2966 isolates lacking obvious risk factors, 579 were part of geo-temporal clusters, whereas 2387 were classified as MRSA of unknown origin (MUOs). We also observed marked differences in the proportion of isolates that belonged to geo-temporal clusters between specific multi-locus variable number of tandem repeat analysis (MLVA) clonal complexes, indicating lineage-specific transmissibility. The majority of clustered isolates (74%) were present in multi-institutional clusters. CONCLUSION: The frequency of MRSA of unknown origin among patients lacking obvious risk factors is an indication of a largely undefined extra-institutional but genetically highly diverse reservoir. Efforts to understand the emergence and spread of high-risk clones require the pooling of routine epidemiological information and typing data into central databases.

Risk factors for sporadic listeriosis in the Netherlands, 2008 to 2013.

Although the disease burden of listeriosis on population level is low, on individual level the impact is high, largely due to severe illness and a high case fatality. Identification of risk factors supports and specifies public health actions needed for prevention. We performed a case­control study to determine host- and food-related risk factors for non-perinatal listeriosis in the Netherlands. Patients with non-perinatal listeriosis reported between July 2008 and December 2013 were compared with controls from a periodic control survey who completed a questionnaire in the same period. Higher age, male sex, underlying disease, especially cancer and kidney disease, and use of immunosuppressive medicine were strong risk factors for acquiring non-perinatal listeriosis. Analysis of the food consumption in the group of cases and controls with underlying diseases did not reveal any high-risk food products. Information and advice should continue to be given to persons at risk of severe listeriosis. Univariate analyses indicate that patients using gastric acid inhibitors are at risk. It is worth adding these patients to the group of susceptible persons.

Risk factors for sporadic Shiga toxin-producing Escherichia coli O157 and non-O157 illness in The Netherlands, 2008-2012, using periodically surveyed controls.

Shiga toxin-producing Escherichia coli (STEC) infections have been associated with severe illness. Ruminants are seen as the main reservoir and the major transmission route is considered to be foodborne. In The Netherlands, a case-control study was conducted, using data collected during 2008-2012. Patients were interviewed and controls completed a self-administered questionnaire. Patients travelling abroad were excluded from the analyses. STEC O157 and non-O157 were examined separately and differentiated into two age groups (<10 years, ⩾10 years). We included 130 O157 cases, 78 non-O157 cases and 1563 controls. In both age groups of O157 patients, raw spreadable sausage was the main risk factor for infection. For STEC non-O157 cases aged <10 years, contact with farm animals was the main risk factor and in non-O157 cases aged ⩾10 years, consumption of beef was the main risk factor. During 2008-2012, risk factors for STEC infections in the Dutch population differed between age groups and serogroup categories, and were related to eating meat and contact with farm animals. Advising the public about the risks of consuming raw or undercooked meat (products) and hygiene habits in case of contact with farm animals, could help in the prevention of STEC infections.

Outbreak of Salmonella Thompson in the Netherlands since July 2012.

An ongoing outbreak of salmonellosis due to Salmonella Thompson is affecting the Netherlands. Between 2 August and 19 October 2012, 866 cases were confirmed. Their median age was 44 years (range: 0-95 years), 63% were female and 36% were hospitalised. A matched case-control study suggested smoked salmon as the vehicle. Salmonella Thompson was confirmed in four of nine batches of smoked salmon from one producer. A recall of all concerned smoked salmon products was executed starting end of September.

Molecular characterisation of PFGE non-typable methicillin-resistant Staphylococcus aureus in The Netherlands, 2007.

In 2007 in The Netherlands, 30% of all human isolates of methicillin-resistant Staphylococcus aureus (MRSA) sent to the National Institute for Public Health and the Environment could not be typed by pulsed-field gel electrophoresis (non-typable (NT)-MRSA). Molecular characterisation of the NT-MRSA isolates revealed 27 different spa types and two distinct SCCmec types, type IV and V. All NT-MRSA isolates were closely related based on spa and multi-locus sequence typing and belonged to the ST398 lineage. The rapid increase of NT-MRSA (ST398) isolates over the last years shows the importance of this relatively new clonal lineage.

Meticillin-resistant Staphylococcus aureus epidemiology and transmission in a Dutch hospital.

The application of the search and destroy (S&D) policy in Scandinavian and Dutch hospitals is associated with low rates of meticillin-resistant Staphylococcus aureus (MRSA). The objective of our study was to describe the MRSA epidemiology and transmission in a Dutch hospital. This descriptive study was performed in a teaching hospital with approximately 40,000 admissions per year. In this hospital the MRSA S&D policy has been applied for several decades. MRSA epidemiology was studied during the years 2001 to 2006. The transmission rate in this hospital was determined using (1) patient's history, (2) relation in time and place to other patients or healthcare workers (HCWs), and (3) molecular typing (pulsed-field gel electrophoresis and Spa). Ninety-five persons were identified as MRSA carriers, namely 82 patients and 13 HCWs. The annual MRSA incidence increased more than three-fold during the study period, which was entirely caused by animal-related MRSA. Twenty-three percent of the patients acquired MRSA in a foreign hospital, 26% via animals, 16% by nosocomial transmission, 4% in another Dutch healthcare institution, 10% in the community via a known MRSA-positive person, and in 22% the source was unknown. For HCWs, 69% of MRSA was due to nosocomial transmission, 15% was related to working in a foreign hospital and in 15% HCWs became colonised via an MRSA-positive partner or relative. The transmission rate of 0.30 (22 secondary cases from 73 index cases) indicates that the spread of MRSA was under control during the study period, and so the S&D policy should be continued.

A beef-associated outbreak of Salmonella Typhimurium DT104 in The Netherlands with implications for national and international policy.

A ten-fold increase in Salmonella Typhimurium DT104 cases in The Netherlands during September-November 2005 prompted an outbreak investigation. A population-based matched case-control study included 56 cases and 100 controls. Risk factors for infection were consumption of a pre-processed raw beef product (odds ratio 4.2, 95% confidence interval 1.5-12.0) and of food from mobile caterers (odds ratio 4.9, 95% confidence interval 1.1-22.1). Bacterial molecular typing established a link with another DT104 outbreak in Denmark caused by beef from a third European country. The incriminated beef was traced in The Netherlands and sampling yielded DT104 of the outbreak-associated molecular type. We concluded that this outbreak was caused by imported contaminated beef. Consumers should be informed about presence of raw meat in pre-processed food products. Optimal utilization of international networks and testing and traceability of foodstuffs has the potential to prevent foodborne infections.

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.

Transmission of a Panton-Valentine leucocidin-positive, methicillin-resistant Staphylococcus aureus strain between humans and a dog.

Panton-Valentine leucocidin-positive methicillin-resistant Staphylococcus aureus (MRSA) strains with identical resistance patterns were cultured from recurrent infections of a 51-year-old patient, her healthy husband, son, and dog, and pulsed-field gel electrophoresis showed that all MRSA strains were indistinguishable.

Emergence of virulent methicillin-resistant Staphylococcus aureus strains carrying Panton-Valentine leucocidin genes in The Netherlands.

Methicillin-resistant Staphylococcus aureus (MRSA) strains carrying the Panton-Valentine leucocidin (PVL) genes have been reported worldwide and are a serious threat to public health. The PVL genes encode a highly potent toxin which is involved in severe skin infections and necrotizing pneumonia, even in previously healthy individuals. We assessed the prevalence of PVL-positive MRSA in The Netherlands for two periods of time: (i) 1987 through 1995 and (ii) 2000 and 2002, and determined their characteristics by using multilocus sequence typing and staphylococcal chromosome cassette (SCCmec) typing. It was found that up to 15% of all MRSA isolates detected in The Netherlands harbored the PVL genes. Most PVL-positive MRSA isolates were obtained from severe soft tissue infections in relatively young individuals. The first PVL-positive MRSA described in The Netherlands, isolated in 1988, was a single-locus variant of the "Berlin" epidemic MRSA clone. The 20 PVL-positive MRSA isolates studied in 2000 and 2002 consisted of five different sequence types (STs) that belonged to four clonal complexes. One of the STs, ST80, is considered to be a widespread European clone and was the most predominant ST (60%) in this study, while ST37 had never been found to be associated with PVL-positive MRSA. Most isolates harbored SCCmec type IV, a supposed marker for community-acquired MRSA. The number and type of virulence-associated genes varied among the different STs.

Panton-Valentine leukocidin positive MRSA in 2003: the Dutch situation.

Analysis of methicillin-resistant Staphylococcus aureus (MRSA) isolates in the Netherlands in 2003 revealed that 8% of the hospital isolates carried the loci for Panton-Valentine leukocidin (PVL). Molecular subtyping showed that most Dutch PVL-MRSA genotypes corresponded to well-documented global epidemic types. The most common PVL-MRSA genotypes were sequence type ST8, ST22, ST30, ST59 and ST80. MRSA with ST8 increased in the Netherlands from 1% in 2002 to 17% in 2003. It is emphasised that PVL-MRSA might not only emerge in the community, but also in the hospital environment.

Methicillin-resistant staphylococci isolated from animals.

Staphylococci isolated from animals (n=311) were screened for methicillin resistance by oxacillin agar screening. Oxacillin-resistant strains were tested for the presence of the mecA gene by PCR. Isolates were identified by standard techniques and 16S rDNA analysis, and their antimicrobial susceptibilities were tested using an agar diffusion method. MecA-positive strains were further analyzed using pulsed-field gel electrophoresis (PFGE). From 11 multidrug-resistant staphylococci, 6 were mecA-positive: 2 methicillin-resistant Staphylococcus aureus (MRSA) and 4 Staphylococcus haemolyticus. Screening of 300 staphylococci (100 S. aureus, 100 S. intermedius and 100 coagulase-negative staphylococci (CNS)) randomly chosen from the strain collection of the Veterinary Microbiological Diagnostic Center yielded five oxacillin-resistant coagulase-negative staphylococci, four of which were mecA-positive. PFGE showed that all mecA-positive staphylococci isolated from animals had distinct patterns. However, one MRSA isolated from a flank fistula of a dog showed homology to a human epidemic MRSA cluster, suggesting that transfer of MRSA between humans and dogs might occur.

Widespread dissemination in The Netherlands of the epidemic berlin methicillin-resistant Staphylococcus aureus clone with low-level resistance to oxacillin.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen and represents a growing public health burden due to the emergence and spread of epidemic strains, particularly within the hospital environment. An epidemic MRSA clone, with characteristic low-level resistance to oxacillin, emerged in the year 2000 and became endemic in the Netherlands. Multilocus sequence typing characterized the strain as sequence type 45, which was previously designated the Berlin epidemic MRSA clone. In 2 years, this strain has become the predominant MRSA clone in the Netherlands.

Panton-Valentine leukocidin positive MRSA in 2003: the Dutch situation.

Analysis of methicillin-resistant Staphylococcus aureus (MRSA) isolates in the Netherlands in 2003 revealed that 8% of the hospital isolates carried the loci for Panton-Valentine leukocidin (PVL). Molecular subtyping showed that most Dutch PVL-MRSA genotypes corresponded to well-documented global epidemic types. The most common PVL-MRSA genotypes were sequence type ST8, ST22, ST30, ST59 and ST80. MRSA with ST8 increased in the Netherlands from 1% in 2002 to 17% in 2003. It is emphasised that PVL-MRSA might not only emerge in the community, but also in the hospital environment.

Sero types, phage types and antibiotic susceptibilities of Salmonella strains isolated from horses in The Netherlands from 1993 to 2000.

We studied 232 Salmonella strains from horses with salmonellosis in The Netherlands, isolated in the period from 1993 to 2000 in order to provide insight in the dynamics of sero-, phage types (pt) and antibiotic susceptibilities over time. The strains were tested for susceptibility to seven antimicrobial agents using the agar diffusion method. In addition, the isolates were sero typed and Salmonella enterica subspecies enterica Typhimurium and Enteritidis strains were further phage typed. S. Typhimurium strains of phage type 506 and 401 (both classified as DT 104 in the English phage typing system) were additionally tested for their susceptibility to chloramphenicol (C), streptomycin (S) and sulfonamides (Su). Resistance was common against tetracycline and ampicillin. Most strains were susceptible to enrofloxacin (Enr) and ceftiofur (Cef). Resistance to tetracycline (T), kanamycin (K), ampicillin (A) and trimethoprim/sulfonamide (Sxt) combinations decreased from 1993 to 2000, whereas the resistance to gentamicin (G), ceftiofur and enrofloxacin was stable over time. S. Typhimurium was the predominant serovar and showed more (multiple) resistance compared to other Salmonella serovars. Sixteen different resistance patterns were found, with resistance to T alone and the combination of ACSSuT and AKSxtT being the most common. The multiresistant S. typhimurium phage type 506 (DT 104) was the most common phage type isolated from horses and most of these strains showed the pentadrug resistance pattern ACSSuT. The S. Typhimurium phage type 401 (DT 104) was also found frequently with an ASSuT resistance pattern. The most common S. Typhimurium phage types in horses corresponded with those found in humans, pigs and cattle in the same period in The Netherlands.

Nosocomial infection by Staphylococcus haemolyticus and typing methods for epidemiological study.

A patient with chronic myelogenous leukemia became colonized with a Staphylococcus haemolyticus strain and experienced a septic episode caused by this strain during a cytostatic course. The strain was multiply resistant to antibiotics; the MIC and MBC of vancomycin were 2 and 4 mg/liter, and the MIC and MBC of teicoplanin were 4 and 16 mg/liter, respectively. We performed a surveillance study on the carriage of S. haemolyticus in medical and nursing staff of the hospital ward where the patient was treated. S. haemolyticus was isolated from 18 sites on 12 of the 39 people tested. A number of typing methods were performed in order to investigate the possible relationships among the isolates. Methods used were immunoblotting of staphylococcal peptides, plasmid analysis, restriction fragment length polymorphism of chromosomal DNA, and pulsed-field gel electrophoresis of total DNA. Compared with the immunoblotting technique, the molecular methods were more discriminative. The strain colonizing the patient showed a consistent pattern by all typing methods during isolation. When the immunoblot technique was used, similar patterns were found with isolates from hospital staff and isolates from unrelated sources. With the molecular techniques, no evidence of a local spread of the patient's strain was found. However, plasmid profiles and restriction fragment length polymorphism and pulsed-field gel electrophoresis patterns showed that S. haemolyticus isolates collected from hospital ward personnel were related, which was not the case with isolates collected from unrelated sources. Restriction fragment length polymorphism analysis was more discriminative when IS431 was used as a DNA probe instead of a probe based on the 16S rRNA gene. S. haemolyticus, as in this case, may develop resistance to vancomycin and teicoplanin. These antibiotics are considered the last-resort drugs for the therapy of nosocomial gram-positive infections. Thus, local spread of staphylococci resistant to these drugs is an important problem, which should be prevented by strict hygienic measures and antibiotic policy.