This study provides strong, novel evidence that humans may introduce methicillin-resistant Staphylococcus aureus CC398 into closed pig populations; it also demonstrates that stringent control and eradication measures were effective and prevented dissemination from pig farms to the general human population.

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Farm animals have been identified as an emerging reservoir for transmission of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) to humans. The low incidence of MRSA in humans and farm animals in Norway has led to the implementation of a national strategy of surveillance and control of LA-MRSA aiming to prevent livestock becoming a domestic source of MRSA to humans. In 2015, MRSA clonal complex 1 spa-type t177 was identified in nine Norwegian pig herds in two neighboring counties. An outbreak investigation was undertaken, and measures of control through eradication were imposed. We performed a register-based cohort study including pig herds and MRSA-positive persons in Norway between 2008 and 2016 to investigate the livestock-association of MRSA CC1, the transmission of the outbreak strain to humans before and after control measures, and the effect of control measures imposed. Data from the Norwegian Surveillance System of Communicable Diseases were merged with data collected through outbreak investigations for LA-MRSA, the National Registry and the Norwegian Register for Health Personnel. Whole-genome sequencing was performed on isolates from livestock and humans identified through contact tracing, in addition to t177 and t127 isolates diagnosed in persons in the same counties. It is likely that a farm worker introduced MRSA CC1 to a sow farm, and further transmission to eight fattening pig farms through trade of live pigs confirmed the potential for livestock association of this MRSA type. The outbreak strain formed a distinct phylogenetic cluster which in addition to the pig farms included one sheep herd and five exposed persons. None of the investigated isolates from possible cases without direct contact to the MRSA positive farms were phylogenetically related to the outbreak strain. Moreover, isolates of t177 or t127 from healthcare and community-acquired cases were not closely related to the outbreak cluster. Eradication measures imposed were effective in eliminating MRSA t177 from the positive pig holdings, and the outbreak strain was not detected in the national pig population or in persons from these counties after control measures.

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A multidrug-resistant, methicillin-resistant Staphylococcus aureus (MRSA) clone, PVL-positive ST772-MRSA-V, named the Bengal Bay clone, is emerging worldwide. In Norway, where MRSA prevalence is low, a sudden increase in ST772-MRSA-V initiated a nationwide molecular epidemiological study. Clinical data were obtained from the Norwegian Surveillance System for Communicable Diseases (MSIS). S. aureus isolates were characterised by antibiotic susceptibility profiles and comprehensive genotyping (spa typing, MLVA, DNA microarray). ST772-MRSA was detected in 145 individuals during 2004-2014, with 60% of cases occurring in 2013-2014. Median age was 31 years and male/female ratio 1.16. The majority had a family background from the Indian subcontinent (70%). MRSA acquisition was mainly reported as unknown (39%) or abroad (42%), the latter associated with a home-country visit (59%), tourism (16%), and immigration (13%). Clinical infection was present in 75%, predominantly by SSTI (83%), 18% were admitted to hospital and 42% were linked to small-scale outbreaks (n = 25). All isolates were multidrug-resistant. Most isolates were resistant to erythromycin, gentamicin and norfloxacin. Genotyping revealed a conserved clone predominated by spa type t657 (83%), MLVA-type 432 (67%) and the genes lukF/S, sea, sec/sel, egc, scn, cna, ccrAA/ccrC, agrII and cap5. A few untypical ccr gene combinations were detected. Bengal Bay isolates have likely been imported on several occasions and revision of infection control guidelines may prevent further spread.

BackgroundPatients with methicillin-resistant S. aureus (MRSA) are thought to incur additional costs for hospitals due to longer stay and contact isolation. The aim of this study was to assess the costs associated with MRSA in Norwegian hospitals.MethodsAnalyses were based on data fromSouth-Eastern Norway for the year 2012 as registered in the Norwegian Surveillance System for Communicable Diseases and the Norwegian Patient Registry. We used a matched case-control method to compare MRSA diagnosed inpatients with non-MRSA inpatients in terms of length of stay, readmissions within 30 days from discharge, as well as the Diagnosis-Related Group (DRG) based costs.ResultsNorwegian patients with MRSA stayed on average 8 days longer in hospital than controls, corresponding to a ratio of mean duration of 2.08 (CI 95%, 1.75–2.47) times longer.A total of 14% of MRSA positive inpatients were readmitted compared to 10% among controls. However, the risk of readmission was not significantly higher for patients with MRSA. DRG based hospital costs were 0.37 (95% CI, 0.19–0.54) times higher among cases than controls, with a mean cost of EUR13,233(SD 26,899) and EUR7198(SD 18,159) respectively.ConclusionThe results of this study indicate that Norwegian patients with MRSA have longer hospital stays, and higher costs than those without MRSA.

IntroductionScandinavian countries have traditionally had a low prevalence of resistant organisms, but have in recent years experienced a change in their epidemiology. We aim to describe the epidemiology of carbapenemase-producing organisms (CPOs), vancomycin-resistant enterococci (VRE) and methicillin-resistant S. aureus (MRSA) in Norway, measure the importance of infections contracted abroad, and assess the morbidity and mortality associated with these resistant bacteria in Norway.Methods and materialsWe used data from the Norwegian surveillance system for communicable diseases covering all findings of the selected resistant bacteria including both infections and colonisation, in the period 2006–2017. Annual trends were assessed using negative binomial regression. For MRSA, we were able to calculate the Morisita-Horn index and transmission numbers following importation in order to assess the effect this had on further domestic transmission.ResultsThe incidence rates (per 100,000 personyears) of the three groups of resistant bacteria have increased during the period. In 2017 the incidence rates were 0.82 for CPOs, 7.09 for VRE and 43.8 for MRSA. 81% of CPO cases were diagnosed in hospitals, but 73% were infected abroad. Most VRE cases were infected in Norwegian hospitals, 85% were associated with hospitals outbreaks. MRSA was predominantly diagnosed in the community, only 21% were diagnosed in hospitals. Of all MRSA cases, 35% were infected in other countries. Most MRSA spa-types were not identified again after introduction, resulting in a transmission of MRSA equivalent to a mean of 0.30 persons infected from each spa-type identified (range: 0–22). The proportion of infections among all notified cases within each diagnose was 44% for MRSA, 9% for VRE and 45% for CPOs. Among persons notified with bacteraemia, the 30 days all-cause mortality were 20%, 16% and 50% for MRSA, VRE and CPOs respectively.DiscussionThe incidence rates of CPOs, VRE and MRSA in Norway are low, but increasing. The continuing increase of notified resistant bacteria highlights the need for a revision of existing infection prevention and control guidelines.