Methicillin-resistant Staphylococcus Aureus Carriage Research Articles

European Society of Clinical Microbiology and Infectious Diseases/European Committee on infection control clinical guidelines on pre-operative decolonization and targeted prophylaxis in patients colonized by multidrug-resistant Gram-positive bacteria before surgery

ScopeThe aim of these guidelines is to provide recommendations for decolonization and perioperative antibiotic prophylaxis (PAP) in multidrug-resistant Gram-positive bacteria (MDR-GPB) adult carriers before inpatient surgery. MethodsThese European Society of Clinical Microbiology and Infectious Diseases/European Committee on Infection Control guidelines were developed following a systematic review of published studies targeting methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, methicillin-resistant coagulase-negative Staphylococci, and pan-drug-resistant-GPB. Critical outcomes were the occurrence of surgical site infections (SSIs) caused by the colonizing MDR-GPB and SSIs-attributable mortality. Important outcomes included the occurrence of SSIs caused by any pathogen, hospital-acquired infections, all-cause mortality, and adverse events associated with the interventions, including resistance development to the agents used and the incidence of Clostridioides difficile infections. The last search of all databases was performed on 1 November 2023. The level of evidence and the strength of each recommendation were defined according to the Grading of Recommendations Assessment, Development, and Evaluation approach. Consensus of a multidisciplinary expert panel was reached for the final list of recommendations. Antimicrobial stewardship considerations were included. RecommendationsThe guideline panel reviewed the impact of decolonization, targeted PAP, and combined interventions (e.g. decolonization and targeted PAP) on the risk of SSIs and other outcomes in MDR-GPB carriers, according to the type of bacteria and type of surgery.We recommend screening for S. aureus before high-risk operations, such as cardiothoracic and orthopaedic surgery. Decolonization with intranasal mupirocin with or without a chlorhexidine bath is recommended in patients colonized with S. aureus before cardiothoracic and orthopaedic surgery and suggested in other surgeries. The addition of vancomycin to standard prophylaxis is suggested for MRSA carriers in cardiothoracic surgery, orthopaedic surgery, and neurosurgery. Combined interventions (e.g. decolonization and targeted prophylaxis) are suggested for MRSA carriers undergoing cardiothoracic and orthopaedic surgery. No recommendation could be made regarding screening, decolonization and targeted prophylaxis for vancomycin-resistant enterococci because of the lack of data. No evidence was retrieved for methicillin-resistant coagulase-negative Staphylococci and pan-drug-resistant-GPB. Careful consideration of the laboratory workload and involvement of antimicrobial stewardship and infection control teams are warranted before implementing screening procedures or performing changes in PAP policy. Future research should focus on novel decolonizing techniques, on the monitoring of resistance to decolonizing agents and PAP regimens, and on standardized combined interventions in high-quality studies.

Isolation of community-associated methicillin-resistant Staphylococcus aureus (MRSA) sequence type (ST) 30 from house rats (Rattus tanezumi) in Hong Kong.

Methicillin-resistant Staphylococcus aureus (MRSA) is of major public health concern due to its resistance to multiple antibiotics. This resistance has been observed in various settings, including hospitals and communities, and has been detected in both animals and humans. Although peridomestic rat species (Rattus spp.) are well described reservoirs of several human pathogens and antimicrobial resistant bacteria, little is known about their role in MRSA epidemiology. In order to investigate whether Rattus spp. in Hong Kong are potential carriers of MRSA, 221 rats were caught from various ecological areas and nasopharyngeal samples were cultured on MRSA selective media. Genotypic characteristics of MRSA were confirmed by whole genome sequencing. Two clonal sequence type (ST) 30 MRSA isolates, harbouring mecA on staphylococcal chromosome cassette (SCC) mec type IVc, were cultured from two house rats (Rattus tanezumi) caught in two densely populated urban areas. To the best of the authors' knowledge, this is the first detection of community-associated (CA)-MRSA strain ST30 SCCmec IVc in peridomestic rodents in Hong Kong and globally. Our finding indicates that house rats can be carriers of MRSA strains that are widely distributed in the community.

Assessing Mupirocin Resistance in MRSA Isolates in Hospitals in Cleveland, OH and Detroit, MI

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen responsible for nosocomial and community-acquired infections with high morbidity and mortality1. MRSA nasal colonization is a major risk factor for developing infection in the hospital setting2,3. Decolonization of MRSA carriers is a strategy to decrease recurrence or to prevent new MRSA infections3,4. Decolonization with nasal mupirocin 2% and chlorhexidine baths has been shown to decrease the risk of MRSA infection after hospital discharge3. Mupirocin is an RNA synthetase inhibitor with activity against MRSA5. Resistance of MRSA isolates to mupirocin has been described previously6. As topical disinfectants play a crucial role in prevention of MRSA infection in a variety of settings, it is important to monitor the emergence of resistance. The goal of this study was to determine the prevalence of mupirocin resistance among MRSA samples isolated from two different regions in the United States (U.S). Methods: Our study had a total of 474 MRSA samples that were obtained from hospitals in Detroit, MI (287 samples) and Cleveland, OH (187 samples). After whole genome sequencing using NextSeq (Illumina Inc., CA) platform the data was analyzed using ResFinder 4.1, to identify antimicrobial resistance which can be either acquired or chromosomally mediated mutations. To visualize the presence of genes of interest the resistance genes were tallied on a spread sheet. Results: Mupirocin resistance gene was detected in five of 287 (1.74%) MRSA samples from the Detroit hospitals, all of which were associated with the mupA gene. Samples collected from the Cleveland area hospital demonstrated mupirocin resistance in seven samples of 187 (3.74%), all associated again with the mupA gene. One sample from the Detroit group showed resistance to both mupirocin and chlorhexidine. Conclusions: Prevalence of mupirocin resistance gene varied between the two hospital locations. Resistance to mupirocin has been documented in association with mutations in the mupA gene as well as chromosomal point mutations that can lead to either low or high-level resistance7,8. Although the mechanisms are not fully clear, mupA gene has been associated with high-level resistance9. Mupirocin resistance among MRSA isolates has increased over time9. MRSA infections remain an important etiology of nosocomial and community-acquired infections and common practice to combat this issue is universal decolonization with mupirocin10. It is critical to understand and monitor for development of mupirocin resistance as mupirocin remains one of the most effective tools to prevent invasive infection with MRSA in many patient populations.

Prevalence of and Risk Factors Associated with Methicillin-Resistant Staphylococcus aureus (MRSA) Carriage Among Cutting Specialties at the Ospital ng Maynila Medical Center

Objective: To determine the point prevalence of, and risk factors associated with MRSA carriage among resident physicians of surgical departments at the Ospital ng Maynila Medical Center. Methods: Design: Cross-sectional Study Setting: Tertiary Government Training Hospital Participants:51 resident physicians from different surgical departments (general surgery, obstetrics and gynecology, ophthalmology, otorhinolaryngology – head and neck surgery and dermatology) underwent nasal and pharyngeal swabs with microbial culture and sensitivity testing to identify MRSA carriers. Fisher Exact Test and logistic regression were utilized to determine associations between MRSA carriage and various risk factors including frequency of hand washing and departmental affiliation. Results: Overall prevalence rate of MRSA carriage was 9.8%. Otorhinolaryngology residents had the highest combined prevalence of MRSA of 42.9%, significantly higher compared to other departments and were used as a reference in logistic regression analyses. Notably, handwashing only once daily was associated with a 20-fold increase in the risk of MRSA carriage (OR 20.5, 95% CI: 1.82 to 230, p = .014). Other departments did not demonstrate statistically significant differences in MRSA carriage rates. Conclusions: Otorhinolaryngology resident physicians had the highest combined prevalence of MRSA and nasal MRSA was found only in otorhinolaryngology residents. The surgical subspecialty and frequency of handwashing of the healthcare worker were identified as important risk factors to develop MRSA carriage. Targeted interventions (including enhanced infection control protocols and regular screening) are needed especially in high-risk departments.

Prevalence of Methicillin-Resistant Staphylococcus aureus in Nasal Cavity of Medical Students at Shendi University, Sudan

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is becoming ever more prevalent in Sudan, and the proportion of MRSA to methicillin-sensitive Staphylococcus aureus (MSSA) seems to be increasing. New strains of MRSA are ever-developing resistance to antibiotic treatment, increasing morbidity and mortality rate.
 Objectives: To detect the prevalence of methicillin-resistant Staphylococcus aureus in the nasal cavity of medical students at Shendi University and to detect variations of MRSA Colonization between student smokers and non-smoker students.
 Methodology: 60 swabs were collected from medical students of Shendi University, culture, and direct gram stain were done, then the plates were examined for any significant bacterial growth. The isolated bacteria were then identified by colonial morphology, indirect gram stain, and biochemical tests.
 Results: All data were analyzed using Statistical Package for Social Sciences (SPSS). Of these, 66.7 % (40/60) were males. 33.3% (20/60) were females. The isolated organism was Staphylococcus aureus 24 (40%), with no growth 36 (60%). The study showed that the overall resistance of Staphylococcus aureus to Methicillin was 21 (35%) and 3 (5%) Sensitive to Methicillin. Methicillin-resistant Staphylococcus aureus cases were found in nine (100%) of the students who smoked and twelve (80%) of the students who did not smoke. Of the pupils who did not smoke, three (20%) had Staphylococcus aureus. Methicillin Sensitive.
 Conclusion: The carriage rate of S. aureus is consistent with similar studies. MRSA carriage in this university study appears high as compared to the general population. Although this study did not confirm a variety of risk factors for the carriage of MRSA previously identified by others, university healthcare personnel should be aware of the changing epidemiology of MRSA and the preventive measures needed to avoid outbreaks.

Predictors for multidrug-resistant organisms (MDROs) carriage in haemodialysis patients.

Infections in haemodialysis (HD) patients are an important cause of morbidity, hospitalization, and mortality. Patients undergoing HD are more prone to develop bacterial infections by multidrug-resistant organisms (MDROs). This study is aimed to detect MDROs colonization in HD patients and its associated risk factors and outcome. A total of 62 nasal swabs and 124 rectal swabs were collected from 62 patients coming to the haemodialysis unit from of March to May 2021 and were further screened for MRSA, VRE and CRE. Out of 62 patients, 22.59% showed the presence of methicillin-resistant staphylococcus aureus (MRSA) while VRE was present in four patients (4/62). CRE was found as 24.2% (15/62). Duration of dialysis was found as a significant risk factor-associated MRSA carriage, Whereas Charlson index and drug and medication were found as significant risk factor for VRE carriage. HD patients are particularly vulnerable to life threatening infections. Therefore, continuous epidemiological surveillance for these MDROs, including genotypic analysis and implementation of adequate decolonization strategies, is crucial and will reduce the possibility of autoinfection as well as disrupt transmission of multi-resistant isolates to others.

Assessing the Concordance of MRSA Carriage Screening With MRSA Infections.

This study focused on children with confirmed methicillin-resistant Staphylococcus aureus (MRSA) infections to determine MRSA screening utility in guiding empirical anti-MRSA treatment of children without history of MRSA infection. We examined the concordance of screens to assess differences by infection type and used statistical analysis to determine significant contributors to concordance. Pediatric hospital patients admitted from 2002 through 2022 were included. Subjects had MRSA infections subsequent to MRSA surveillance screens performed the preceding year. Statistical analysis identified associations between MRSA screens and infections. Number needed to treat analysis calculated the utility of rescreening. Among 246 subjects, 39.0% had concordant screens; 151 (61.4%) screens were obtained in the 2 weeks preceding infection. Sensitivity for bacteremia was 50.0% (n = 42), for endotracheal/respiratory 44.4% (n = 81), and 29.4% (n = 102) for skin and soft-tissue infection. For children aged younger than 6 months, sensitivity was 35.9% (n = 78). Multivariable analysis significantly associated days since screening with decreasing likelihood of concordance. Regression modeled the probability of concordance to drop below 50.0% for all infections after 4 days, after 6 days for bacteremia specifically, and 12 days for endotracheal/respiratory infections. The concordance of screens was far lower than negative predictive values found previously; earlier studies were possibly impacted by low prevalence and exclusion of children at high risk to inform high negative predictive values. We suggest that negative MRSA screens should not invalidate reasonable suspicion for MRSA infection in patients with high pretest probabilities.

Genetic Determinants in MRSA Carriage and Their Association with Decolonization Outcome

Methicillin-resistant Staphylococcus aureus (MRSA) colonization increases the risk of infection. Response to decolonization treatment is highly variable and determinants for successful decolonization or failure of eradication treatment are largely unknown. Insight into genetic predictors of eradication failure is potentially useful in clinical practice. The aim of this study was to explore genetic characteristics that are associated with MRSA decolonization failure. This cohort study was performed in a tertiary care hospital in the Netherlands. Patients with ≥ 1 positive MRSA culture from any site and with available whole -genome sequencing data of the MRSA isolate between 2017 and 2022 were included. Lineages, resistance, and virulence factors were stratified by MRSA decolonization outcome. In total, 56 patients were included: 12/56 (21%) with treatment failure and 44/56 (79%) with successful decolonization (with or without preceding treatment). A significant association was found between ciprofloxacin-resistant lineages and failure of eradication (OR 4.20, 95%CI 1.11–15.96, P = 0.04). Furthermore, livestock-associated MRSA and the major community-associated MRSA lineages ST6-t304 and ST8-t008 were associated with successful eradication treatment or spontaneous clearance. In conclusion, this explorative study showed a higher eradication failure rate in complicated MRSA carriers with ciprofloxacin-resistant MRSA lineages, which are predominantly healthcare-associated. Further studies are warranted to confirm the higher eradication failure risk of ciprofloxacin-resistant lineages, and identify the underlying mechanisms.

Within-host genomic evolution of methicillin-resistant Staphylococcus aureus in long-term carriers

Assessing the genomic evolution of Staphylococcus aureus can help us understand how the bacteria adapt to its environment. In this study, we aimed to assess the mutation rate within 144 methicillin-resistant Staphylococcus aureus (MRSA) carriers with a carriage time from 4 to 11 years, including some carriers who belonged to the same households. We found that 23 of the 144 individuals had completely different MRSA types over time and were therefore not long-term carriers of the same MRSA. From the remaining 121 individuals, we performed whole-genome sequencing (WGS) on 424 isolates and then compared these pairwise using core genome multilocus sequence typing (cgMLST) and single-nucleotide polymorphism (SNP) analyses. We found a median within-host mutation rate in long-term MRSA carriers of 4.9 (3.4–6.9) SNPs/genome/year and 2.7 (1.8–4.2) allelic differences/genome/year, when excluding presumed recombination. Furthermore, we stratified the cohort into subgroups and found no significant difference between the median mutation rate of members of households, individuals with presumed continued exposure, e.g., from travel and persons without known continued exposure. Finally, we found that SNPs occurred at random within the genes in our cohort.Key points• Median mutation rate within long-term MRSA carriers of 4.9 (3.4–6.9) SNPs/genome/year• Similar median mutation rates in subgroups (households, travelers)• No hotspots for SNPs within the genome

Impact of discontinuation of contact precautions on surveillance- and whole genome sequencing-defined methicillin-resistant Staphylococcus aureus healthcare-associated infections.

Prior studies evaluating the impact of discontinuation of contact precautions (DcCP) on methicillin-resistant Staphylococcus aureus (MRSA) outcomes have characterized all healthcare-associated infections (HAIs) rather than those likely preventable by contact precautions. We aimed to analyze the impact of DcCP on the rate of MRSA HAI including transmission events identified through whole genome sequencing (WGS) surveillance. Quasi experimental interrupted time series. Acute care medical center. Inpatients. The effect of DcCP (use of gowns and gloves) for encounters among patients with MRSA carriage was evaluated using time series analysis of MRSA HAI rates from January 2019 through December 2022, compared to WGS-defined attributable transmission events before and after DcCP in December 2020. The MRSA HAI rate was 4.22/10,000 patient days before and 2.98/10,000 patient days after DcCP (incidence rate ratio [IRR] 0.71 [95% confidence interval 0.56-0.89]) with a significant immediate decrease (P = .001). There were 7 WGS-defined attributable transmission events before and 11 events after DcCP (incident rate ratio 0.90 [95% confidence interval 0.30-2.55]). DcCP did not result in an increase in MRSA HAI or, in WGS-defined attributable transmission events. Comprehensive analyses of the effect of transmission prevention measures should include outcomes specifically measuring transmission-associated HAI.

Nasal carriage of methicillin and inducible clindamycin resistant Staphylococcus aureus among healthcare workers in a tertiary care hospital, Kathmandu, Nepal

Introduction and Objectives: Transmission of methicillin-resistant Staphylococcus aureus (MRSA) from healthcare workers is one of the most frequent causes of nosocomial infections globally. There is a significant burden of nosocomial MRSA infections in low and low-middle income countries (LMICs), including Nepal. The present study investigated the rate of nasal carriage of MRSA among the healthcare workers in a tertiary care hospital, in Kathmandu, Nepal with emphasis on inducible macrolide-lincosamide-streptogramin B (iMLSB) resistance. Material and method: The study was conducted at Star Hospital, Lalitpur, Nepal, from September 2022 to November 2022. Healthcare workers (HCWs) working at the diffeerent departments of the hospital were enrolled. Nasal swabs from both anterior nares of HCWs were collected aseptically and cultured on Mannitol Salt agar. S. aureus was identified by Gram stain and standard biochemical tests. Antibiotic susceptibility of S. aureus was performed by disc diffusion method. MRSA isolates were detected phenotypically by disc diffusion method using cefoxitin disc (30 µg), and inducible clindamycin resistance was detected phenotypically by the D-zone test. Results: Total 105 HCWs were enrolled in the study. Out of 105 HCWs, 14 (13.3%) were positive for S. aureus among which 6 (5.7%) were MRSA carriers. The nasal carriage of MRSA was highest among doctors (16.7%) and the HCWs of the post-operative department (14.3%). All the isolated MRSA were susceptible to chloramphenicol and vancomycin. Inducible MLSB resistance was detected in 33.3% MRSA while the rate was 21.4% in all isolated S. aureus. Conclusion: The study demonstrated that HCWs could be the potential source of nosocomial infection by methicillin and inducible clindamycin resistant S. aureus. Thus, preventive measures should be initiated to mitigate the risk of its spread and the test for detection of inducible clindamycin resistance should be incorporated into the routine antibiotic susceptibility testing in hospital settings. IMC J Med Sci. 2024; 18(1):005. DOI: https://doi.org/10.55010/imcjms.18.005 *Correspondence: Gaurab Pandey, Non-Communicable Disease Laboratory, National Public Health Laboratory, Teku, Kathmandu, 44600, Nepal; E-mail: pandeygaurab67@gmail.com

Association between methicillin-resistant Staphylococcus aureus nasal carriage and infection after pancreatic surgery.

Methicillin-resistant Staphylococcus aureus (MRSA) infections after pancreatectomy are relatively rare; however, they can be fatal when associated with pseudoaneurysms. For the past 12 years, we have been investigating nasal MRSA carriage by polymerase chain reaction testing, postoperatively in patients admitted to the intensive care units, to prevent nosocomial infections. Here, we investigated the relationship between MRSA nasal carriage and postoperative MRSA infection at the surgical site, following pancreatectomy. This single-center retrospective study analyzed 313 pancreatectomies (220 pancreaticoduodenectomies and 93 distal pancreatectomies), performed at our hospital between January 2011 and June 2022. The incidence of surgical site infection (SSI) and postoperative MRSA infection were compared between the nasal MRSA-positive and nasal MRSA-negative groups. MRSA nasal carriage was identified in 24 cases (7.6%), and the frequency of SSIs in the nasal MRSA-positive and MRSA-negative groups were 50% and 36.7%, respectively, with no significant difference (p = .273). However, the frequency of MRSA infection among the SSI cases was significantly higher in the nasal MRSA-positive group (16.7%) than in the nasal MRSA-negative group (1.7%) (p = .003). It should be noted that MRSA carriers have a significantly higher frequency of MRSA-positive SSIs.

Prevalence study of methicillin resistant <i>Staphylococcus aureus</i> and its SCC<i>mec</i> features in horses and handlers in Zaria and Kaduna, Nigeria

Methicillin resistant Staphylococcus aureus (MRSA) is a pathogen with public health implications being resistant to most used antibiotics. It has been associated with health facilities but has now become prevalent in community settings. The presence of MRSA in 240 apparently healthy horses and 65 horse handlers in Kaduna and Zaria was studied through nasal swabs collection by a one-stage cluster sampling and analysed using standard microbiological tests and genotyping methods. Questionnaires were also administered to assess for risk factors associated with MRSA carriage. Prevalence was 10% and 6.2% from the horses and horse handlers respectively. The S. aureus isolates showed highest resistance rates of 54.6% to penicillin and oxacillin. There were high resistance rates also to erythromycin, and tetracycline of 47.7% and 34.1% respectively. Resistance of 22.7% to amikacin and gentamicin, 6.8% to sulphamethoxazole+trimethoprim, 2.3% to ciprofloxacin, and 2.3% to chloramphenicol were also observed. Multidrug resistance (MDR) was found among 74.8% of the MRSA isolates. SCCmec typing showed types I, III, and IV in both the horses and the horse handlers while one horse was found to carry SCCmec V. Possible risk factors identified for MRSA carriage by horse handlers included being a veterinarian, exposure to antimicrobial agents, healthcare facility visitation, and personal hygiene. For the horses, risk factors from this study were allergy and wound management. MRSA nasal carriage in horses and horse handlers, as well as MDR (multidrug resistant) strains of S. aureus have been established from this study, this is of public health concern.

SCREENING OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS AMONG HEALTHCARE WORKERS AND THEIR ANTIBIOTIC SUSCEPTIBILITY PATTERN IN A TERTIARY CARE HOSPITAL

Objective: Colonization of Staphylococcus aureus in the nasal flora has been proven to play an important role in the transmission of infections. Health care workers carrying Staphylococcus aureus in their nose or skin play an important role in cross-contamination and thus result in Methicillin-resistant Staphylococcus aureus (MRSA) related hospital-acquired or community-acquired infections. Implementation of hand hygiene methods and standard precautions are helpful in reducing transmission and controlling spread. Screening for carriage of MRSA is fundamental step in nosocomial infection control. The present study was undertaken to determine the prevalence of MRSA carriage rate and study their antibiogram.
 Methods: A cross-sectional study was conducted for a period of six months and samples from 185 HCWs working in high-risk areas were processed by standard protocols. As per CLSI guidelines, MRSA detection by disc diffusion method using Cefoxitin disc (30μg) and further determined by Epsilometer test (E-test) by interpreting Minimum inhibitory concentration (MIC) values (mcg/ml).
 Results: Out of 185 nasal swabs, 53 were Staphylococcus aureus isolates. MRSA colonization is seen in (8.64%) samples. Preponderance was seen in staff nurses (10.16%). Antibiogram of MRSA isolates showed sensitivity to Vancomycin and linezolid.
 Conclusion: The present study was undertaken to screen nasal carriage of MRSA among healthcare workers, as they pose a potential risk factor for nosocomial transmission leading to MRSA outbreaks. The strengthening of Infection prevention and control measures institutionalization of antimicrobial stewardship programs helps in curbing the spread of MRSA.

Molecular characterization of MRSA collected during national surveillance between 2008 and 2019 in the Netherlands

Background.Although the Netherlands is a country with a low endemic level, methicillin-resistant Staphylococcus aureus (MRSA) poses a significant health care problem. Therefore, high coverage national MRSA surveillance has been in place since 1989. To monitor possible changes in the type-distribution and emergence of resistance and virulence, MRSA isolates are molecularly characterized.Methods.All 43,321 isolates from 36,520 persons, collected 2008–2019, were typed by multiple-locus variable number tandem repeats analysis (MLVA) with simultaneous PCR detection of the mecA, mecC and lukF-PV genes, indicative for PVL. Next-generation sequencing data of 4991 isolates from 4798 persons were used for whole genome multi-locus sequence typing (wgMLST) and identification of resistance and virulence genes.Results.We show temporal change in the molecular characteristics of the MRSA population with the proportion of PVL-positive isolates increasing from 15% in 2008–2010 to 25% in 2017–2019. In livestock-associated MRSA obtained from humans, PVL-positivity increases to 6% in 2017–2019 with isolates predominantly from regions with few pig farms. wgMLST reveals the presence of 35 genogroups with distinct resistance, virulence gene profiles and specimen origin. Typing shows prolonged persistent MRSA carriage with a mean carriage period of 407 days. There is a clear spatial and a weak temporal relationship between isolates that clustered in wgMLST, indicative for regional spread of MRSA strains.Conclusions.Using molecular characterization, this exceptionally large study shows genomic changes in the MRSA population at the national level. It reveals waxing and waning of types and genogroups and an increasing proportion of PVL-positive MRSA.

Identification of Vancomycin Resistance in Methicillin-resistant Staphylococcus aureus in two macaque species and decolonization and long-term prevention of recolonization in Cynomolgus Macaques (Macaca fascicularis).

Methicillin-resistant Staphylococcus aureus (MRSA) is a S. aureus strain with resistance to beta-lactam antibiotics, making it a global human and veterinary health concern. Specifically, immunosuppressed patients have a remarkably higher risk of clinical MRSA infections with significantly increased rates of prolonged clinical recovery, morbidity, and mortality. The current treatment of choice for MRSA is vancomycin. Importantly, we report the first known vancomycin-resistant S. aureus (VRSA) carriers in a cohort of Mauritian cynomolgus macaques (CM) imported to the Oregon National Primate Research Center (ONPRC), with a MRSA carrier rate of 76.9% (10/13 animals). All MRSA isolates also demonstrated resistance to vancomycin with prevalence of vancomycin-intermediate Staphylococcus aureus (VISA) at 30% (3/10 MRSA-positive CMs) and VRSA at 70% (7/10 MRSA-positive CMs). Additionally, we identified VRSA in a rhesus macaque (RM) housed within the same room as the VRSA-positive CMs and identified a MRSA/VISA carrier rate of 18.8% in RMs (3/16 positive for both MRSA and VISA) in unexposed recently assigned animals directly from the ONPRC RM breeding colony. Considering that the MRSA and VRSA/VISA-positive CMs future study aims included significant immunosuppression, MRSA/VRSA/VISA decolonization treatment and expanded "MRSA-free" practices were employed to maintain this status. We report the first controlled study using in-depth analyses with appropriate diagnostic serial testing to definitively show an MRSA decolonization therapy (90% success rate) and expanded barrier practice techniques to successfully prevent recolonization (100%) of a cohort of CMs MRSA-free (up to 529 days with a total of 4,806 MRSA-free NHP days).

Pilot study on nasal microbiota dynamics and MRSA carriage of a pig cohort housed on straw bedding.

Methicillin-resistant Staphylococcus aureus (MRSA) can be transmitted between pigs and humans on farms. Hence, the reduction of MRSA carriage in pigs could decrease the risk of zoonotic transmission. Recently, straw bedding has been found to significantly reduce MRSA carriage in pigs. The mechanisms behind this effect remain unclear but changes in the nasal microbiome may play a role. In this exploratory study, the nasal microbiota of pigs kept on straw was examined using V1/V2 16S rRNA gene sequencing. Nasal swabs were collected from 13 pigs at six different time points during the course of a full fattening cycle resulting in 74 porcine samples. In addition, straw samples were collected at each time point. Eleven out of 13 pigs were MRSA positive at housing-in. We found a strong temporal pattern in the microbial communities. Both microbial diversity and abundance of Staphylococcus species peaked in week 5 after introduction to the straw stable decreased in week 10, when all pigs turned MRSA-negative, and increased again toward the end of the fattening period. These findings show that the introduction of pigs into a new environment has a huge impact on their nasal microbiota, which might lead to unfavorable conditions for MRSA. Moreover, other Staphylococcus species may play a role in eliminating MRSA carriage. We designed a follow-up study including two different husbandry systems to further assess these effects.

Does universal nasal/skin decolonization in nursing homes affect risk factors for MRSA carriage?

Background: A regional decolonization intervention (SHIELD-OC) involving universal chlorhexidine for routine bathing and 5 days of twice-daily nasal iodophor every other week in nursing homes (NHs) recently demonstrated marked reductions in multidrug-resistant organisms, all-cause hospitalizations, and infection-related hospitalizations in Orange County, California. Specific to methicillin-resistant Staphylococcus aureus (MRSA), NH prevalence (nares, skin, or perirectal) decreased from 43% to 29%. Methods: We conducted a retrospective cohort study evaluating the impact of decolonization on factors associated with MRSA carriage. The cohort included residents from 18 SHIELD-OC NHs who were sampled for MRSA using nares, axilla, groin, and perirectal cultures. A point-prevalence survey was conducted in 2016–2017 (before decolonization, 50 randomly sampled residents per NH) and in 2018–2019 (decolonization, all residents sampled). Resident characteristics were obtained from their most proximal admission, quarterly, and/or discharge assessment using data mandated for NH reporting (CMS minimum data set), and included demographics, medical devices, comorbidities (including Alzheimer’s disease and related dementias or ADRD), and mobility and hygiene needs. We used generalized-linear mixed models stratified by decolonization and clustered by NH to identify differences in factors associated with MRSA carriage. Results: Of the 2,351NH residents, 2,255 (96%) had characteristics available in the CMS data set. Of the 2,255 residents included, 774 (34%) were MRSA carriers. Before decolonization, medical devices (OR, 2.5), limited mobility (OR, 1.6), and diabetes (OR, 1.4) were significantly associated with MRSA carriage in an adjusted model (Table). During decolonization, these effects were mitigated (medical device OR, 2.5–1.1; diabetes OR, 1.4–0.9) and were no longer significantly associated with MRSA carriage. Male sex appeared to have more of an effect in the decolonization phase (OR, 1.3–1.6), but limited mobility remained stable (OR, 1.6–1.7). Several variables were collinear. Presence of a medical device was collinear with postacute stays (<100 days) and Medicaid insurance. Limited mobility was associated with limited ability for hygienic self-care. ADRD was collinear with age. Final adjusted models accounted for medical devices, limited mobility, diabetes, ADRD, cancer, sex, and ethnicity. Conclusions: In a large interventional cohort of 18 NHs, factors associated with MRSA carriage changed after adoption of universal decolonization. Specifically, the increased risk of MRSA associated with medical devices and diabetes were substantially mitigated by decolonization, suggesting that these risks are modifiable. These long-term care findings are consistent with clinical trials showing reductions in MRSA carriage after implementing chlorhexidine bathing in ICUs and in non-ICU patients with devices. The ability of decolonization to attenuate the risk of MRSA carriage among diabetics or other potential high-risk groups deserves further study.Disclosures: None

The Emergence of Mupirocin Resistance among Staphylococcus aureus in a Tertiary Care Hospital in South India: The Necessity for Routine Susceptibility Testing

Methicillin-resistant Staphylococcus aureus (MRSA) is difficult to treat, causing considerable morbidity and mortality. Nasal carriage of MRSA can occur both in healthcare workers and patients. Mupirocin is used as a topical agent for the eradication of such isolates. The present study aims to study the prevalence of mupirocin resistance among the MRSA and MSSA (Methicillin-sensitive Staphylococcus aureus) isolates. A total of 148 Staphylococcus aureus isolates were tested. Antibiotic susceptibility testing was done by Kirby Bauer disc diffusion method for amoxicillin, penicillin, cotrimoxazole, clindamycin, mupirocin(5 µg and 200 µg discs for low and high-level resistance), erythromycin, gentamicin and linezolid. MRSA isolates were detected by cefoxitin disc diffusion and Mec A detection by PCR (Polymerase Chain Reaction). MRSA was detected among 44 (29.7%) of the isolates. Among MSSA, good susceptibility was observed for cotrimoxazole 89 (85.5%) and clindamycin 92 (88.4%). An overall mupirocin resistance of 12(8.1%) was observed, with high-level resistance at 4 (2.7%) and low-level resistance at 8 (5.4%).The mupirocin resistance pattern between MRSA and MSSA was not statistically significant (p=0.1833). The emergence of mupirocin resistance highlights the necessity for creating cognizance among clinicians before prescribing mupirocin. In eradicating nasal carriage of MRSA, all the isolates should always be tested for mupirocin susceptibility to prevent the selection and spread of drug-resistant isolates.

Hiding in Plain Sight: Benefit of Abrasion and Laceration Swabs in Identification of Panton-Valentine Leucocidin (PVL)-Meticillin Resistant Staphylococcus aureus (MRSA) Colonisation in Military Personnel.

Background Outbreaks of Panton-Valentine Leucocidin (PVL)-producing methicillin-resistantStaphylococcus aureus(MRSA) skin and soft tissue infections (SSTIs) are a recurrent challenge for the Royal Marines at the Commando Training Centre (CTCRM). The intensity of commando training, its impact on skin integrity, and persistent colonisation reservoirs within the training centre have thwarted attempts to prevent these outbreaks. Aim To present an outbreak of PVL-producing MRSA SSTIs at a military training centre, demonstrating the benefit of additional abrasion and laceration swabs on the identification of colonised personnel and showing the effectiveness of a 10-day decolonisation regime. Method Following the identification of the outbreak of PVL-producing MRSA, all 36 members of the Recruit Troop underwent nasal MRSA screening to identify MRSA carriers. The screening was repeated on day 16 after completing an enhanced 10-day decolonisation regime. A third screening was conducted on the 110th day after a second peak of infection was identified. Various infection control measures, such as enhanced cleaning, restriction of movement and adjustments to the military training serials, were introduced to prevent further spread through the training centre. Results In this outbreak, two-thirds (eighteen) of the Recruit Troop suffered MRSA-PVL skin infections requiring antibiotic therapy and three required hospital admission for surgical management of their abscesses. The outbreak lasted 130 days, with two spikes in infections 10 weeks apart. The outbreak was successfully confined to one troop. Conclusion With concerns about low identification rates of carriers using nasal screening for MRSA, in this outbreak, we improved the identification of asymptomatic carriage with the simple step of additional culture swabs for all cuts and abrasions. Improved identification of colonised recruits, along with an enhanced decolonisation regime and rigid infection control practices, prevented the further spread of the clone through the training centre. In a population with constant ongoing skin trauma, such as the military, contact sport athletes and iIV drug users, our results show that a culture of suitable abrasions/lacerations will improve the identification of MRSA colonisation compared with nasal swabs alone. Despite ongoing skin trauma and the logistical difficulties in delivering effective decolonisation during military training, decolonisation was successful in 79% of recruits after one decolonisation and 87% after the second 10-day decolonisation.