Aina Elisabeth Fossum Moen

Nasal carriage of Staphylococcus aureus: frequency and molecular diversity in a randomly sampled Norwegian community population

Skråmm I, Moen AEF, Bukholm G. Nasal carriage of Staphylococcus aureus: frequency and molecular diversity in a randomly sampled Norwegian community population. APMIS 2011; 119: 522–8.

Surgical Site Infections in Orthopaedic Surgery Demonstrate Clones Similar to Those in Orthopaedic Staphylococcus aureus Nasal Carriers

BACKGROUND Staphylococcus aureus is the main microbial pathogen in orthopaedic infections, and it adds considerable extra costs to the national health-care system each year. Nasal carriers of Staphylococcus aureus have an increased risk of invasive disease, including surgical site infection. The purpose of the present study was to investigate whether the Staphylococcus aureus carrier clones found in patients undergoing elective orthopaedic surgery were the same as the clones found in isolates from orthopaedic patients with Staphylococcus aureus surgical site infections. METHODS Patients admitted for elective orthopaedic surgery underwent nasal cultures for Staphylococcus aureus. Further, orthopaedic patients with a deep surgical site infection caused by Staphylococcus aureus were characterized using the same genotyping methods: multilocus sequence typing and staphylococcal protein A typing. RESULTS Multilocus sequence typing revealed a large number of genotypes in the two populations. However, 85% of nasal carriers and 90% of surgical site infection isolates could be classified into the same four multilocus sequence typing clonal complexes. The risk of Staphylococcus aureus surgical site infection in nasal carriers compared with non-carriers was 5.8 times higher (95% confidence interval, 1.5 to 23.1 times). Of the nasal carriers, 6.3% (95% confidence interval, 1.7% to 10.9% [seven of 111 patients]) developed a deep Staphylococcus aureus surgical site infection, and all but one patient had identical genotypes in the nasal and surgical site infection isolates. CONCLUSIONS Staphylococcus aureus isolates from nasal carriers and patients with surgical site infection clustered into the same few multilocus sequence typing clonal complexes. This finding confirms the existence of some commonly occurring Staphylococcus aureus clones in different population groups within a geographically restricted area. The almost complete individual concordance between Staphylococcus aureus genotypes in carriers who developed a deep surgical site infection strongly supports transmission from the nose, skin surfaces, and other endogenous body regions as a possible route. CLINICAL RELEVANCE Surgical site infections might be more frequently caused by endogenous transmission than was previously assumed. Perioperative preventive efforts must focus more on this route to further decrease the risk of postoperative orthopaedic infections.

Methicillin-Resistant Staphylococcus aureus (MRSA) Is Increasing in Norway: A Time Series Analysis of Reported MRSA and Methicillin-Sensitive S. aureus Cases, 1997–2010

Background Accurate estimates of the incidence and prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections are needed to inform public health policies. In Norway, where both MRSA infection and carriage are notifiable conditions, the reported incidence of MRSA is slowly increasing. However, the proportion of MRSA in relation to all S. aureus isolates is unknown, making it difficult to determine if the rising incidence is real or an artifact of an increasing number of tests performed. Aim To characterize recent trends in MRSA infections and obtain a more complete understanding of the MRSA level in Norway. Methods All reported cases of MRSA and methicillin-sensitive S. aureus (MSSA) from Oslo County (1997–2010) and Health Region East (2008–2008), representing approximately 11% and 36% of the Norwegian population, respectively, were analyzed using a stochastic time series analysis to characterize trends. Results In Oslo County, the proportion of methicillin-resistant cases increased from 0.73% to 3.78% during the study period and was well modeled by an exponential growth with a doubling constant of 5.7 years (95% CI 4.5–7.4 years). In Health Region East, the proportion of MRSA cases increased from 0.4% to 2.1% from 2002 to 2008, with a best-fitting linear increase of 0.26% (95% CI 0.21–0.30%) per year. In both cases, the choice of a linear or exponential model for the time trend produced only marginally different model fits. We found no significant changes due to revised national MRSA guidelines published in June 2009. Significant variations in the increasing time trend were observed in the five hospitals within the region. The yearly reported incidence of MSSA was relatively stable in both study areas although we found seasonal patterns with peaks in August. Conclusion The level of MRSA is increasing in Norway, and the proportion of methicillin resistance in all S. aureus isolates are higher than the reported proportion of MRSA in invasive infections.

Distribution of methicillin-resistant Staphylococcus aureus in a low-prevalence area

Investigating circulating methicillin-resistant Staphylococcus aureus (MRSA) strains and identifying their accumulations in society are important in the search for strategies for eradicating the pathogen. The aim of this study was to describe the distribution of MRSA in a low-prevalence area where MRSA could be establishing endemicity. MRSA isolates from 802 patients (803 isolates) were included and placed into a timeline (1991-2006) under different categories: hospital (n=270), long-term care facility (LTCF) (n=175) and general practitioner (GP) (n=358). MRSA isolates had been characterized using multilocus sequence-typing, staphylococcal cassette chromosome mec-typing and detection of Panton-Valentine leukocidin-encoding genes (lukS/F-PVL), and were placed in exotoxin-encoding gene clusters. The GP category increased mainly in a cluster with few exotoxin-encoding genes (r=0.760), the LTCF (r=0.804) and the hospital category (r=0.876) mainly in clusters with more exotoxin-encoding genes. ST8-IV, lukS/F-PVL present, increased in the community (1-41 isolates) in the time period 2002-2006, later in the hospital (1-8 isolates, 2004-2006), and finally reached the LTCF (1 isolate, 2006). ST8-IV, lukS/F-PVL absent, could have attained endemicity in LTCFs, where 51 isolates were isolated in 2006. ST125-IV, lukS/F-PVL absent, showing epidemic qualities abroad, caused outbreaks at five LTCFs.

Nasal Carriage of Staphylococcus aureus: Which Sequence Types Do Orthopedic Surgical Healthcare Workers Carry?

Using sequence typing methods, we found that healthcare workers on our orthopedic surgery unit were persistent carriers of a limited number of sequence types of Staphylococcus aureus for a limited time. Multilocus sequence typing characterized 3 clonal complexes that accounted for more than 80% of the clonal complexes identified.

Simultaneous purification of DNA and RNA from microbiota in a single colonic mucosal biopsy

BackgroundNucleic acid purification methods are of importance when performing microbiota studies and especially when analysing the intestinal microbiota as we here find a wide range of different microbes. Various considerations must be taken to lyse the microbial cell wall of each microbe. In the present article, we compare several tissue lysis steps and commercial purification kits, to achieve a joint RNA and DNA purification protocol for the purpose of investigating the microbiota and the microbiota-host interactions in a single colonic mucosal tissue sample.ResultsA further optimised tissue homogenisation and lysis protocol comprising mechanical bead beating, lysis buffer replacement and enzymatic treatment, in combination with the AllPrep DNA/RNA Mini Kit (Qiagen, Hilden, Germany) resulted in efficient and simultaneous purification of microbial and human RNA and DNA from a single mucosal colonic tissue sample.ConclusionsThe present work provides a unique possibility to study RNA and DNA from the same mucosal biopsy sample, making a direct comparison between metabolically active microbes and total microbial DNA. The protocol also offers an opportunity to investigate other members of a microbiota such as viruses, fungi and micro-eukaryotes, and moreover the possibility to extract data on microbiota and host interactions from one single mucosal biopsy.

USA300 methicillin‐resistant Staphylococcus aureus in Norway

Moen AEF*, Tannæs TM, Leegaard TM. USA300 methicillin‐resistant Staphylococcus aureus (MRSA) in Norway.

MRSA infections in Norway: A study of the temporal evolution, 2006-2015

Background Norway has one of the lowest prevalences of methicillin-resistant Staphylococcus aureus (MRSA) infections in the world. This study exploits the extensive data on MRSA infections in the Norwegian surveillance system to investigate the important factors defining the MRSA epidemiology. Methods We performed a quasi-Poisson regression of the monthly notification rate (NR) of MRSA infections reported from January 2006 to December 2015, comparing the time trend among people with an immigrant vs. Norwegian background and domestic vs. imported infections, stratified by age groups. Findings A total of 5289 MRSA infections were reported during the study period, of which 2255 (42·6%) were acquired in Norway, 1370 (25·9%) abroad, and 1664 (31·5%) with an unknown place of acquisition. Overall, the monthly NR increased significantly from 2006 to 2015 (+0·8% each month). The monthly increase in immigrants (+1·3%) was steeper than that in people with a Norwegian background (+0·6%). There was a significant growth (+0·4%) in the rate of domestically acquired infections, however, the NR of infections acquired abroad increased faster (+0·8%). For both imported and domestic infections, the increase occurred in persons aged < 70 years. Interpretation Our analysis suggests that immigration and importation, especially among persons aged < 40 years, represent important factors for the increasing notification rate of MRSA infections in Norway.

Challenges in the identification of methicillin-resistant Staphylococcus argenteus by routine diagnostics

Current clinical diagnostic procedures have shortcomings in the differentiation of Staphylococcus argenteus from Staphylococcus aureus. This article presents three cases of Staphylococcus argenteus obtained from clinical samples. The initial results from biochemical and molecular methods led to an incorrect identification of the isolates as methicillin‐resistant Staphylococcus aureus. Whole genome sequencing and real‐time PCR targeting the nonribosomal peptide synthetase gene led to their correct identification as methicillin‐resistant Staphylococcus argenteus. The study shows that real‐time PCR can be used to differentiate the two species in routine diagnostics. For purposes of identification based on whole genome sequencing, the MinION portable sequencer is a simple and affordable approach which could be used by many laboratories.

Studying the time trend of Methicillin-resistant Staphylococcus aureus (MRSA) in Norway by use of non-stationary γ-Poisson distributions

Objectives Study the time development of methicillin-resistant Staphylococcus aureus (MRSA) and forecast future behaviour. The major question: Is the number of MRSA isolates in Norway increasing and will it continue to increase? Design Time trend analysis using non-stationary γ-Poisson distributions. Setting Two data sets were analysed. The first data set (data set I) consists of all MRSA isolates collected in Oslo County from 1997 to 2010; the study area includes the Norwegian capital of Oslo and nearby surrounding areas, covering approximately 11% of the Norwegian population. The second data set (data set II) consists of all MRSA isolates collected in Health Region East from 2002 to 2011. Health Region East consists of Oslo County and four neighbouring counties, and is the most populated area of Norway. Participants Both data sets I and II consist of all persons in the area and time period described in the Settings, from whom MRSA have been isolated. Primary and secondary outcome measures MRSA infections have been mandatory notifiable in Norway since 1995, and MRSA colonisation since 2004. In the time period studied, all bacterial samples in Norway have been sent to a medical microbiological laboratory at the regional hospital for testing. In collaboration with the regional hospitals in five counties, we have collected all MRSA findings in the South-Eastern part of Norway over long time periods. Results On an average, a linear or exponential increase in MRSA numbers was observed in the data sets. A Poisson process with increasing intensity did not capture the dispersion of the time series, but a γ-Poisson process showed good agreement and captured the overdispersion. The numerical model showed numerical internal consistency. Conclusions In the present study, we find that the number of MRSA isolates is increasing in the most populated area of Norway during the time period studied. We also forecast a continuous increase until the year 2017.