Prevalence of methicillin-resistant Staphylococcus aureus nasal colonization among Taiwanese children in 2005 and 2006

A Method Based on a Modified Fluorescence In Situ Hybridization (FISH) Approach for the Sensing of Staphylococcus aureus from Nasal Samples

Staphylococcus aureus is a major source of bacteremia and develops several complications, causing high morbidity and mortality. Rapid identification and detection of these bacteria have become an important issue for biomedical applications. Herein, an optical method based on a modified fluorescence in situ hybridization (FISH) approach has been established using DNA hybridization technology for the swift detection of pathogenic S. aureus from clinical samples. The platform was constructed with single-stranded genomic DNA and microbial colony by directly immobilizing in agarose-polyvinyl alcohol (AG-PVA) hydrogel on the surface of a glass slide. The probe was based on an elongation factor encoding the tuf gene, which binds with equal affinity to single-stranded DNA targets as well as surface proteins on microbial cells. The probe was labeled with MFP488 fluorophore having excitation wavelength 501 nm. The hybridization of the labeled probe with the target DNA and surface proteins was carried out under optimal FISH conditions, and the detection of bacteria was based on temporary field excitation of the labeled probe under a fluorescence microscope. Positive hybridization signals were detected by high fluorescence intensity. In comparison to genomic DNA, robust signals were observed with microbial cells, perhaps due to the moonlighting effect of the elongation factor Tu (Ef-Tu) expressed on the surface of bacterial cells. The applicability of the developed platform was tested on pediatric nasal samples, and results were verified with real-time qPCR. The designed platform is stable and sensitive, and after detailed optimization, a portable structure for on-site detection of pathogenic bacteria from clinical samples can be produced.

Discrimination of Methicillin-resistant Staphylococcus aureus by MALDI-TOF Mass Spectrometry with Machine Learning Techniques in Patients with Staphylococcus aureus Bacteremia

Early administration of proper antibiotics is considered to improve the clinical outcomes of Staphylococcus aureus bacteremia (SAB), but routine clinical antimicrobial susceptibility testing takes an additional 24 h after species identification. Recent studies elucidated matrix-assisted laser desorption/ionization time-of-flight mass spectra to discriminate methicillin-resistant strains (MRSA) or even incorporated with machine learning (ML) techniques. However, no universally applicable mass peaks were revealed, which means that the discrimination model might need to be established or calibrated by local strains’ data. Here, a clinically feasible workflow was provided. We collected mass spectra from SAB patients over an 8-month duration and preprocessed by binning with reference peaks. Machine learning models were trained and tested by samples independently of the first six months and the following two months, respectively. The ML models were optimized by genetic algorithm (GA). The accuracy, sensitivity, specificity, and AUC of the independent testing of the best model, i.e., SVM, under the optimal parameters were 87%, 75%, 95%, and 87%, respectively. In summary, almost all resistant results were truly resistant, implying that physicians might escalate antibiotics for MRSA 24 h earlier. This report presents an attainable method for clinical laboratories to build an MRSA model and boost the performance using their local data.

Community-Associated Methicillin-Resistant Staphylococcus Aureus Colonization in a Birth Cohort of Early Childhood: The Role of Maternal Carriage

Background: Methicillin-resistant Staphylococcus aureus (MRSA) colonization in infants may pose a risk for subsequent infection in children. The study aimed to determine S. aureus colonization patterns in infancy, and strain relatedness between maternal and infant colonization.

Methods: A prospective cohort study was conducted for nasopharyngeal S. aureus detection in neonates at delivery; in children at 1, 6, 12, 24, 36, and 60 months of age; and from mothers immediately after the delivery of their baby and when their child is 1 month old. A questionnaire for infants and mothers was administered at each planned visit.

Results: In total, 521 and 135 infant–mother dyads underwent nasopharyngeal swab collection at 1 month and immediately after delivery, respectively. Among the 521 dyads at 1 month of age, concordant S. aureus colonization was found in 95 dyads, including MRSA in 48.4% (46/95). No concordant MRSA carriage was present among the 135 dyads at delivery. The genetic relatedness of concurrent MRSA-colonized dyads showed that more than two-thirds (32/46 [69.6%]) had identical genotypes, mainly ST 59/PVL-negative/SCCmec IV. Infants aged 1 month had the highest incidence of S. aureus, and the trend declined to a nadir at the age of 12 months. Carrier mothers who smoked cigarettes may increase the risk of infant Staphylococcus colonization (odds ratio, 2.12; 95% confidence interval, 1.23–3.66; p < 0.01).

Conclusions: Maternal–infant horizontal transmission may be the primary source of MRSA acquisition in early infancy. The avoidance of passive smoking could be recommended for the prevention of S. aureus carriage.

A longitudinal molecular surveillance of clinical methicillin-resistant Staphylococcus aureus isolates in neonatal units in a teaching hospital, 2003-2018

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has been an important nosocomial pathogen in our neonatal units since 1990s. To understand the longitudinal changing molecular epidemiology of these MRSA isolates, we conducted this study.

MATERIALS

From 2003 to 2018, we collected clinical MRSA isolates from 536 infants hospitalized at neonatal units of a medical center in northern Taiwan. First isolate from each infant was characterized.

RESULTS

The case/isolate number ranged from 7 cases/isolates (the lowest) in 2010 to 71 cases/isolates (the highest) in 2004. Of the 536 isolates, a total of 15 pulsotypes were identified. Three major clones were identified and characterized as sequence type (ST) 239/pulsotype A/staphylococcal chromosomal cassette (SCC) mec III/Panton-Valentine leukocidin (PVL)-negative, accounting for 22.2% of the isolates, ST59/pulsotype C/SCCmec IV/PVL-negative, accounting for 34.3% and ST59/pulsotype D/SCCmec V_T/PVL-positive, accounting for 30.0%. The first clone (hospital strains) dominated in the first two years, and became weakened from 2005 through 2016. Clonal complex (CC) 59 (combined the second and third clones) dominated (>50% of the isolates) from 2005 through 2018. One community clone (ST573) demonstrated a marked increase since 2007 and vanished abruptly since 2010. Several minor MRSA clones emerged after 2010.

CONCLUSION

The molecular epidemiology of MRSA isolates in our neonatal units from 2003 to 2018 revealed that an epidemic as well as endemic hospital clone of ST239 dominated before 2005 and was replaced by the local community clone of CC59 thereafter.

Nasal Methicillin-Resistant Staphylococcus aureus Colonization in Patients with Type 1 Diabetes in Taiwan

Nasal methicillin-resistant Staphylococcus aureus (MRSA) colonies are an essential reservoir of infection, especially for patients with diabetes. However, data on MRSA colonization in patients with type 1 diabetes are limited. We investigated the epidemiology of MRSA colonization in patients with type 1 diabetes. This prospective cross-sectional study was conducted in a medical center (Chang Gung Memorial Hospital) in Taiwan from 1 July to 31 December 2020. Nasal sampling and MRSA detection were performed. The molecular characteristics of MRSA isolates were tested, and factors associated with MRSA colonization were analyzed. We included 245 patients with type 1 diabetes; nasal MRSA colonization was identified in 13 (5.3%) patients. All isolates belonged to community-associated MRSA genetic strains; the most frequent strain was clonal complex 45 (53.8%), followed by ST59 (30.8%) (a local community strain). MRSA colonization was positively associated with age ≤ 10 years, body mass index < 18 kg/m², and diabetes duration < 10 years; moreover, it was negatively associated with serum low-density lipoprotein cholesterol ≥ 100 mg/dL. No independent factor was reported. The nasal MRSA colonization rate in type 1 diabetes is approximately 5% in Taiwan. Most of these colonizing strains are community strains, namely clonal complex 45 and ST59.

Staphylococcus aureus ST59: Concurrent but Separate Evolution of North American and East Asian Lineages

Despite initially being described in North America, Staphylococcus aureus (SA) sequence type ST59 is the most commonly isolated sequence type in Eastern Asia. The origins and evolution of this strain type remains unclear and therefore we gathered a collection of ST59 isolates from Canada and mainland China for a detailed genetic analysis of the lineage. Bayesian inference phylogenomic analysis of our isolates, along with previously published ST59 sequences indicated that the lineage could be divided into 6 distinct subgroups (WGS-1 thorough 6), each having distinct molecular characteristics. Analysis also demonstrated the concurrent but separate evolution of North American and East Asian lineages, as well as the extensive diversification of the East Asian lineage. The presence of a mobile element structure (MES) was found to be the major difference between these two continental lineages, absent in all North American isolates, and present in all East Asian ones. Other mobile genetic elements, such as the Immune Evasion Complex (IEC), Panton Valentine Leukocidin (PVL), and Staphylococcal Cassette Chromosome mec (SCCmec), showed significant variability within each sub-group and likely represents local selective pressures rather than major characteristics defining the groups. Our analysis also demonstrated the existence of a more ancient ST59 sub-lineage from North America, which was MES negative and contained some of the earliest reported ST59 isolates. Combined with the existence of a MES negative isolate from Taiwan, predicted to have appeared prior to diversification of the East Asian lineages, these results hint at the possibility of a North American origin for the lineage, which gained hold in Eastern Asia following acquisition of MES, and subsequently diversified.

Characterization of SCCmec, Spa Types and Multidrug Resistant of Methicillin-Resistant Staphylococcus aureus Isolates in Ahvaz, Iran

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most pathogens associated with health care. Molecular typing methods are vital for outbreak investigations of MRSA. The aim of this study was characterization of SCCmec, spa types and multidrug resistant of methicillin-resistant Staphylococcus aureus isolates in Ahvaz, Iran.

Methods

A total of 50 MRSA isolates were determined by using the phenotypic method and mecA gene. Antibiotic resistance profile and SCCmec types were screened using disc diffusion method and PCR, respectively. For spa typing of MRSA isolates, two molecular typing methods including the PCR-sequencing and high-resolution melting (HRM) analysis were used.

Results

In the present study, the highest sensitivity of MRSA was to vancomycin and linezolid and the lowest to clindamycin. In the MRSA isolates, 22% were XDR and 78% were MDR. SCCmec type III was found commonly among MRSA. Based on PCR-sequencing and HRM results, 10 different spa types were identified. The spa types t037 and t030 were the most common in this study.

Conclusion

This study emphasizes the spa variation among MRSA isolates, which may be considered as an important criterion when treating staphylococcal infections. Accurate and early detection of MDR, XDR, or even PDR MRSA isolates strains must be commenced by all clinical microbiology laboratories to reduce the menace of antimicrobial resistance.

Using Core-genome Multilocus Sequence Typing to Monitor the Changing Epidemiology of Methicillin-resistant Staphylococcus aureus in a Teaching Hospital

Background

This study was performed to elucidate the changing epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in a Chinese teaching hospital.

Methods

We performed whole-genome sequencing and phylogenetic analysis on MRSA isolates recovered at Sir Run Run Shaw Hospital (SRRSH) from 2013 to 2015. MRSA isolates underwent susceptibility testing, resistance determinant screening, virulence assays and clinical data analysis.

Results

A total of 292 MRSA infections were identified during the study period. Of these, most belonged to sequence type (ST) 5 (51.4%; 150 of 292) and ST59 (23.3%; 68 of 292). The proportion of ST5 MRSA decreased from 68.3% in 2013 to 32.1% in 2015, and the proportion of ST59 MRSA increased from 8.9% to 41.0%. Core-genome phylogenetic analysis revealed that ST59 MRSA isolates exhibited wider genotypic diversity than ST5 MRSA isolates in both healthcare-onset and community-onset groups. Minimum spanning trees showed that a cluster of ST5 MRSA was circulating at SRRSH, whereas the ST59 MRSA infections were mostly sporadic. ST59 MRSA caused 45.2% of the 93 skin and soft-tissue infection cases and displayed lower levofloxacin (11.8%) and ciprofloxacin (19.1%) resistance rates than the ST239 and ST5 MRSA isolates. ST59 healthcare-onset MRSA displayed enhanced virulence in the skin infection model and hemolysis assays. Notably, these isolates had virulence levels similar to those of classic community-associated MRSA strains.

Conclusions

ST59 MRSA strains with high virulence potential have been replacing ST5 MRSA in predominance in SRRSH and causing nosocomial infections. Whole-genome sequencing is a powerful tool to monitor changes in the epidemiology of MRSA in hospitals.

Prevalence of methicillin-resistant Staphylococcus aureus in healthy Chinese population: A system review and meta-analysis

Objective

To comprehensively determine the prevalence of MRSA in healthy Chinese population, the influencing factors of MRSA colonization and its antibiotic resistance.

Methods

Articles that studied prevalence or influencing factors of MRSA carriage in healthy Chinese population were retrieved from PubMed, Ovid database, three Chinese electronic databases. The pooled prevalence of MRSA, its antibiotic resistance and influencing factors were analyzed by STATA12.0.

Results

37 studies were included. The pooled prevalence of MRSA was 21.2% (95% CI: 18.5%-23.9%), and the prevalence of S.aureus was 15% (95% CI: 10%-19%), with a significant heterogeneity (MRSA: I² = 97.6%, P<0.001; S.aureus: I² = 98.4%, P < 0.001). In subgroup analysis, the pooled prevalence of MRSA was 28% (95%CI: 10%-51%) for Livestock-related workers, 18% (95%CI: 11%-26%) for children, 20% (95%CI: 12%-29%) for healthcare workers, 7% (95%CI: 3%-13%) for community residents. The prevalence of MRSA in studies with oxacillin disk diffusion method (28%, 95%CI: 21%-35%) seemed higher than that with the mecA gene method(12%, 95%CI: 7%-19%). MRSA in studies conducted in Taiwan was more common than in Mainland China and Hong Kong. Similar results were found in meta-regression. Influencing factors for MRSA colonization were noted in seven eligible studies, they included younger age (OR: 3.54, 95% CI: 2.38–5.26; OR: 2.24, 95% CI: 1.73–2.9), attending day care centers (DCCs) (OR: 1.95, 95% CI: 1.4–2.72; OR: 1.53, 95% CI: 1.2–1.95), flu vaccination (OR:1.73, 95% CI: 1.28–2.35), using antibiotics within the past year (OR: 2.05, 95% CI:1.35–3.11), residing in northern Taiwan (OR: 1.45, 95% CI: 1.19–1.77), regular visits to health care facility (OR: 23.83, 95% CI: 2.72–209.01), household member working in health care facility (OR: 8.98, 95% CI:1.4–55.63), and contact with livestock (OR: 6.31, 95% CI: 3.44–11.57). Moreover, MRSA was found to be highly resistant to penicillin, ampicillin, erythromycin, and clindamycin, with a pooled resistance ratio of 100, 93, 88, and 75%, respectively. However, no resistance were noted to vancomycin.

Conclusion

The pooled prevalence of MRSA was considerably high in health Chinese population. Additionally, these strains showed extreme resistance to penicillin, ampicillin, erythromycin and clindamycin. Public MRSA protection measures and the surveillance of MRSA should be strengthened to reduce the spread of MRSA among hospitals, communities, and livestock.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Risk factors for and molecular characteristics of methicillin-resistant Staphylococcus aureus nasal colonization among healthy children in southern Taiwan, 2005-2010

BACKGROUND/PURPOSE

Nasal colonization of Staphylococcus aureus is a well-defined risk factor for subsequent infection. This study investigated the prevalence of methicillin-resistant S. aureus (MRSA) in southern Taiwan and aimed to identify the host factors for S. aureus colonization and the virulence factor of Panton-Valentine Leukocidin (PVL) genes.

METHODS

In a hospital-based study in Kaohsiung from Oct. 2005 to Dec. 2010, we performed nasal swab in the healthy children aged 2-60 months. We examined the relationship between the demographic characteristics and S. aureus nasal colonization. MRSA isolates were further analyzed for antimicrobial susceptibility and molecular characteristics.

RESULTS

Among 3020 healthy children, 840 (27.8%) children had S. aureus nasal colonization. Of 840 isolates, 246 (29.3%) isolates were MRSA. MRSA colonization was significantly associated with age 2-6 months, day care attendance, and influenza vaccination. Breastfeeding was a protective factor against MRSA colonization. Most MRSA isolates were susceptible to trimethoprim-sulfamethoxazole and doxycycline. Ninety-four percent of MRSA isolates carried either type IV staphylococcal cassette chromosome mec (SCCmec) or SCCmec V_T and 87% belonged to the local community strains, namely clonal complex 59/SCCmec IV or V_T. MRSA isolates with PVL-negative was associated with children with passive smoking.

CONCLUSIONS

Between 2005 and 2010, 27.8% and 8.14% of healthy children in southern Taiwan had nasal carriage of S. aureus and MRSA, respectively. Most MRSA isolates were local community strains. Several demographic factors associated with nasal MRSA colonization were identified.

Prevalence and molecular characteristics of methicillin-resistant Staphylococcus aureus among nasal carriage strains isolated from emergency department patients and healthcare workers in central Taiwan

BACKGROUND AND OBJECTIVE

Screening and identification of methicillin-resistant Staphylococcus aureus (MRSA) carriage are helpful for controlling MRSA dissemination in hospitals. The aim of our study was to determine the prevalence of nasal carriages and diversity of MRSA among patients and healthcare workers (HCWs) at two regional hospitals in Taiwan.

METHODS

Nasal swabs were obtained prospectively from 204 patients visiting the emergency department (ED) and 326 HCWs in two regional hospitals in Changhua, Taiwan, between February 2015 and June 2015. All the MRSA isolates were further molecularly characterized.

RESULTS

Of the 204 participating patients, the nasal carriage rates of S. aureus and MRSA were 22.1% and 7.8%, respectively. For HCWs, the S. aureus and MRSA carriage rates were 26.1% and 6.1%, respectively. There was no statistically significant difference in MRSA carriage rate between patients and HCWs (P = 0.447). Patients receiving hemodialysis were significantly associated with MRSA colonization (P = 0.012). The leading three sequence types (ST) were ST59 (16, 44.4%), ST45 (11, 30.6%), and ST239 (3, 8.3%) for all 36 MRSA isolates. ST59/SCCmec IV/t437/PVL-negative and ST45/SCCmec V/t1081/PVL-negative were the predominant clones among HCWs (30%) and participating patients (19%), respectively.

CONCLUSION

Overall, a substantial proportion of patients visiting the ED and HCWs harbored CA-MRSA, mostly ST59 strains, in their nares. It is noteworthy that MRSA ST45 strains supplanted ST239 as the second leading nasal MRSA colonization strain in our study.

Nasal methicillin-resistant Staphylococcus aureus colonization among otherwise healthy children aged between 2 months and 5 years in northern Taiwan, 2005-2010

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have been increasingly reported worldwide and are associated with nasal colonization. In Taiwan, available data disclosed a similar trend. We conducted a study for the updated childhood nasal MRSA carriage.

METHODS

From July 2005 to December 2010, children aged between 2 months and 5 years who presented for a well-child health care visit to a medical center or from kindergarten/daycare center were invited and a nasal swab specimen was obtained for the detection of MRSA. All MRSA isolates were characterized.

RESULTS

A total of 3226 children were included and the rate of nasal MRSA carriage was 10.2%. Children aged 2-6 months and >3 years were significantly associated with MRSA carriage, while pneumococcus colonization (p = 0.033) and breastfeeding (p = 0.025) were negatively associated with MRSA carriage. Of the 330 MRSA isolates, a total of 13 pulsotypes with two major patterns (type C, 47.0% and D, 29%) were identified. Most MRSA isolates belonged to two major clones, characterized as sequence type 59 (ST59)/pulsotype C/staphylococcal cassette chromosome (SCCmec) IV/Panton-Valentine leukocidin (PVL)-negative (45.8%) and ST59/pulsotype D/SCCmec V_T/PVL-positive (22.7%). Two new clones as ST 508/SCCmec IV (9.7%) and ST573/SCCmec IV (7.3%) emerged and increased markedly since 2007.

CONCLUSION

Between 2005 and 2010, 10.2% of healthy children in northern Taiwan carried MRSA in anterior nares, with the highest carriage rate for infants aged 2-6 months. Two emerging clones, ST 508 and ST 573, were identified and the clinical significance needs further surveillance.

Diagnosis and management of Panton-Valentine leukocidin toxin associated Staphylococcus aureus infection: an update

The incidence of invasive Staphylococcus aureus (SA) infection has increased in the past decade and is associated with poor outcomes and high mortality rates. Of all the virulence factors, Panton-Valentine Leukocidin (PVL) has received the greatest attention. PVL producing SA strains are more likely to produce severe skin and soft tissue infections (SSTIs) and necrotizing pneumonia. This review focuses on the current evidence on PVL-SA virulence, epidemiology, clinical disease and treatment with relevance to healthcare in India.

Prevalence of and risk factors for nasal methicillin-resistant Staphylococcus aureus colonization among children in central Taiwan

BACKGROUND/PURPOSE

Staphylococcus aureus (S. aureus) causes diseases ranging from mild skin infections to invasive diseases. Carriage of S. aureus, including methicillin-resistant S. aureus (MRSA), is a significant risk factor for subsequent staphylococcal infection. Several studies discussed MRSA colonization in Taiwan, but mostly in northern Taiwan. This is the first study that estimates the prevalence of MRSA nasal colonization in healthy children and identifies the potential risk factors in central Taiwan.

METHODS

A total of 3144 healthy children aged 2-60 months who visited Taichung Veterans General Hospital (TCVGH) were screened for nasal S. aureus carriage from July 2005 to December 2010. Questionnaires included demographic information and potential risk factors for carriage of S. aureus were completed by parents/guardians.

RESULTS

Prevalence of MSSA and MRSA were 12.09% and 5.25%, respectively. The youngest group aged 2-6 months had the highest S. aureus carriage rate, and the carriage rate revealed a peak in summer. The nasal colonization of Streptococcus pneumoniae (S. pneumoniae) was a protective factor against S. aureus colonization. 85% of the MRSA colonizing isolates belonged to clonal complex 59/staphylococcal cassette chromosome type IV or V_T, the local community clone in Taiwan.

CONCLUSION

An increasing trend of MRSA nasal carriage rate in Taiwan had been brought forward, however, it was not observed in central Taiwan during the period of 2005-2010. We found a summer peak on both MRSA and MSSA carriages.

Longitudinal investigation of nasopharyngeal methicillin-resistant Staphylococcus aureus colonization in early infancy: The PATCH birth cohort study

OBJECTIVES

The study aimed to determine the long-term Staphylococcus aureus colonization patterns and strain relatedness, and the association between maternal and infant colonization in infancy.

METHODS

A birth cohort study was conducted from January 2012 to November 2014. Nasopharyngeal swabs for S. aureus detection were collected from infants at the age of 1, 2, 4, 6 and 12 months and from mothers when their children were 1-month-old.

RESULTS

In total, 254 samples were collected at each planned visit during the first 12-month study. The prevalence of S. aureus colonization decreased in the first year of life, ranging from 61.0% (155/254) at the age of 1 month to 12.2% (31/254) at 12 months. Persistent colonization, defined as a positive culture on four or five occasions, was detected in only 13.8% (35/254) of carriers. Most of the persistent carriers were colonized with methicillin-resistant S. aureus (MRSA) only, and among persistent MRSA carriers, 61.1% (11/18) had indistinguishable genotypes. Of the mothers with MRSA colonization, 77.1% (27/35) had infants who were concomitantly colonized at the age of 1 month; 70.4% (19/27) of the infant-mother paired isolates belonged to indistinguishable or related subtypes, which suggests that surrounding carriers, probably their mothers, may be the possible source for MRSA acquisition in early infancy.

CONCLUSIONS

Staphylococcus aureus colonization including MRSA was commonly observed in our cohort. Strains of persistent MRSA among infant-mother pairs were usually of indistinguishable genotypes. Therefore, horizontal spread within households is possibly an important factor related to infant MRSA colonization.

Changing epidemiology of community-associated methicillin-resistant Staphylococcus aureus in the Asia-Pacific region

INTRODUCTION

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has become an important threat to public health in the Asia-Pacific region, which is characterized by a large population and relatively insufficient resources. Better understanding on the current status of CA-MRSA in the region is of paramount importance. Areas covered: This article reviews the published literatures on the prevalence, molecular epidemiology, colonization, and hospital spread of CA-MRSA. Expert commentary: The burden of CA-MRSA has been increasing in the past two decades. The molecular epidemiology of CA-MRSA in the Asia-Pacific region shows a marked diversity in each country. Still, some strains - multilocus sequence type (MLST) ST59, ST30, ST72, ST8, and ST772 - are unique clones that have successfully established themselves as predominant, often spreading into nosocomial settings. More coordinated and comprehensive surveillance to understand the true epidemiology of CA-MRSA in the Asia-Pacific region is urgently needed.

Methicillin-Resistant Staphylococcus aureus Nasal Colonization in Chinese Children: A Prevalence Meta-Analysis and Review of Influencing Factors

OBJECTIVE

To determine the pooled prevalence and review the influencing factors of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization in Chinese children.

METHODS

Articles published between January 2005 and October 2015 that studied prevalence or influencing factors of MRSA nasal colonization in Chinese children were retrieved from Chinese Biomedical Literature database (CBM), China National Knowledge Infrastructure (CNKI) database, Chinese VIP database, Chinese Wanfang database, Medline database and Ovid database. Prevalence and influencing factors were analyzed by STATA 13.1.

RESULTS

Thirteen articles were included. The overall prevalence of MRSA nasal colonization was 4.4% (95% confidence interval [CI]: 0.027-0.062). With an MRSA prevalence of 3.9% (95% CI: 0.018-0.061) in healthy children and 5.8% (95% CI: 0.025-0.092) in children with underlying medical conditions. Children recruited in the hospitals presented MRSA prevalence of 6.4% (95% CI: 0.037-0.091), which was higher than those recruited in the communities [2.7% (95% CI: 0.012-0.043)]. A number of influencing factors for MRSA nasal colonization were noted in three eligible studies: gender (male vs female; OR: 0.67; 95% CI: 0.55-0.82), younger age (OR: 2.98; 95% CI: 1.31-6.96 and OR: 1.56; 95% CI: 1.21-2.00), attending day care centers (OR: 2.97; 95% CI: 1.28-6.76), having infectious diseases (OR: 2.31; 95% CI: 1.10-4.52), using antibiotics (OR: 2.77; 95% CI: 1.45-5.05), residing in northern Taiwan (OR: 1.41; 95% CI: 1.15-1.71), passive smoking (OR: 1.30; 95% CI: 1.02-1.63), and pneumococcal vaccination (OR: 1.22; 95% CI: 1.01-1.48).

CONCLUSIONS

Children could act as reservoirs of MRSA transmissions. Hospitals remained the most frequent microorganism-circulated settings. More MRSA infection control strategies are required to prevent the dissemination among children.

Identification of Infantile Diarrhea Caused by Breast Milk-Transmitted Staphylococcus aureus Infection

Staphylococcus aureus is a well-known organism which is responsible for a variety of human infectious diseases including skin infections, pneumonia, bacteremia, and endocarditis. Few of the microorganisms can be transmitted from mother to the newborn or infant by milk breastfeeding. This study aims to identify transmission of S. aureus from healthy, lactating mothers to their infants by breastfeeding. Stool specimens of diarrheal infants and breast milk of their mother (totally three pairs) were collected and six Staphylococcus aureus isolates were cultured positively. Homology and molecular characters of isolated strains were tested using pulsed-field gel electrophoresis (PFGE), spa typing, and multilocus sequence typing. Furthermore, toxin genes detection was also performed. Each pair of isolates has the same PFGE type and spa type. Four Sequence types (STs) were found among all the isolates; they are ST15, ST188, and ST59, respectively. Among the strains, seb, sec, and tst genes were found, and all were negative for pvl gene. The homology of the S. aureus strains isolated from the infants' stool and the mothers' milk was genetically demonstrated, which indicated that breastfeeding may be important in the transmission of S. aureus infection, and the character of S. aureus needed to be further evaluated.

Antibiotic susceptibility and genomic variations in Staphylococcus aureus associated with Skin and Soft Tissue Infection (SSTI) disease groups

Background

Staphylococcus aureus is associated with human skin and soft tissue infections (SSTIs); however, the involvement of virulence factors in different clinical presentations is unclear.

Methods

We analyzed methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains from Taiwan to determine correlations among the clinical characteristics of SSTIs, antimicrobial susceptibility and virulence factors of S. aureus with specific genetic backgrounds.

Results

We identified 177 MRSA isolates and 130 MSSA isolates among the 307 SSTI-associated S. aureus isolates. Hospital-acquired (HA)- and community-acquired (CA)-MRSA isolates accounted for 61.6 % and 38.4 % of the isolates, respectively. Clinical presentations in SSTI patients differed significantly for the disease groups. Deep-seated MRSA infections presented with higher amputation rate than MSSA infections. MRSA isolates were all susceptible to linezolid, teicoplanin, and vancomycin, and >94 % of isolates were erythromycin- and clindamycin-resistant. Staphylococcal cassette chromosome (SCCmec) types IV, V, and VII were the most frequent in the CA-MRSA group (n = 68); types III, IV and V were the most frequent in the HA-MRSA group (n = 109). Panton-Valentine leukocidin (PVL) genes were significantly more frequent in CA-MRSA strains (75.0 %) than in HA-MRSA (33.0 %) and MSSA (24.6 %) and were found in 66.7 % (74/111) strains isolated from the abscess group. Exfoliatin A genes were more common in catheter-related exit-site MSSA infections (37.5 %) compared with other MSSA disease groups (P < 0.05). Exfoliatin B and superantigen exotoxin genes were uncommon in all SSTI disease types. Pulsotypes A (ST239), C, and D (ST59) were the predominant MRSA genotypes in deep-seated infections.

Conclusions

If not treated appropriately, deep-seated MRSA-associated infections present with higher amputation rates than deep-seated MSSA-associated infections. PVL-positive MRSA strains caused more frequently pus-forming lesions and less bacteremia and invasive diseases. Methods for discriminating CA-MRSA from HA-MRSA strains are now unreliable due to circulation of both ST 239 and ST 59 strains in the community and nosocomial settings. Initial antibiotic treatments should consider MRSA for patients with SSTIs in areas where MRSA is prevalent.

Novel pandemic influenza A (H1N1) and community-associated methicillin-resistant Staphylococcus aureus pneumonia

Postinfluenza bacterial pneumonia is a leading cause of influenza-associated death, and Staphylococcus aureus and Streptococcus pneumoniae have been important pathogens that have caused pneumonia since the influenza pandemic in 1919. Emergence of novel influenza A (H1N1) pdm09 and the concomitant global spread of community-associated methicillin-resistant S. aureus (CA-MRSA) have led to increasing prevalence of CA-MRSA pneumonia following influenza infection. Such an epidemiologic change poses a therapeutic challenge due to a high risk of inappropriate empiric antimicrobial therapy and poor clinical outcomes. Early diagnosis and initiation of appropriate antimicrobial therapy for post-influenza bacterial pneumonia have become even more important in the era of CA-MRSA. Therefore, novel molecular diagnostic techniques should be applied to more readily diagnose MRSA pneumonia.

Drug resistance and genetic characteristics of clinical isolates of staphylococci in Myanmar: high prevalence of PVL among methicillin-susceptible Staphylococcus aureus belonging to various sequence types

Prevalence, drug resistance and genetic characteristics were analysed for a total of 128 clinical isolates of staphylococci obtained from a tertiary hospital in Myanmar. The dominant species were S. aureus (39%) and S. haemolyticus (35%), followed by S. epidermidis (6%) and S. saprophyticus (5%). The majority of S. haemolyticus isolates (71.1%) harboured mecA, showing high resistance rates to ampicillin, cephalosporins, erythromycin and levofloxacin, while methicillin-resistant S. aureus (MRSA) was only 8% (four isolates) among S. aureus with type IV SCCmec. Panton-Valentine leukocidin (PVL) genes were detected in 20 isolates of S. aureus (40%), among which only one isolate was MRSA belonging to sequence type (ST) 88/agr-III/coa-IIIa, and the other 19 methicillin-susceptible S. aureus (MSSA) isolates were classified into six STs (ST88, ST121, ST1153, ST1155, ST1930, ST3206). An ST1153 MSSA isolate with PVL was revealed to belong to a novel coa type, XIIIa. ST121 S. aureus was the most common in the PVL-positive MSSA (47%, 9/19), harbouring genes of bone sialoprotein and variant of elastin binding protein as a distinctive feature. Although PVL-positive MSSA was susceptible to most of the antimicrobial agents examined, ST1930 isolates were resistant to erythromycin and levofloxacin. ST59 PVL-negative MRSA and MSSA had more resistance genes than other MRSA and PVL-positive MSSA, showing resistance to more antimicrobial agents. This study indicated higher prevalence of mecA associated with multiple drug resistance in S. haemolyticus than in S. aureus, and dissemination of PVL genes to multiple clones of MSSA, with ST121 being dominant, among hospital isolates in Myanmar.

Comparative Molecular Characteristics of Community-Associated and Healthcare-Associated Methicillin-Resistant Staphylococcus aureus Isolates From Adult Patients in Northern Taiwan

Methicillin-resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen in hospitals, and increases rapidly in the community, named as community-associated MRSA (CA-MRSA). We conducted a prospective/retrospective study to understand the epidemiology, antimicrobial susceptibility, and molecular characteristics of MRSA infections in adult patients in Taiwan.From March to June, 2012, all clinical MRSA isolates were prospectively collected from adult patients in a tertiary hospital in northern Taiwan. Selective isolates were further characterized. We reviewed the detailed medical record of each case retrospectively.A total of 857 clinical isolates were collected from 555 patients. A total of 749 isolates from 453 patients were classified as healthcare-associated (HA)-MRSA and 108 isolates from 102 patients as CA-MRSA by the epidemiologic criteria. Compared to HA-MRSA, CA-MRSA isolates were significantly more frequently identified from pus (78% vs 28%, P < 0.001) and less frequently from sputum (4.6% vs 43.8%, P < 0.001) and blood (3.7% vs 15%, P = 0.002). CA-MRSA isolates were more susceptible to all antibiotics tested. A total of 102 CA-MRSA and 101 HA-MRSA isolates were characterized, showing significantly different molecular characteristics between CA and HA isolates (P < 0.001). The clone of sequence type (ST) 59/t437 complex, with 2 pulsotypes, accounted for 70% of CA isolates. Three major clones were identified from HA-MRSA isolates, namely clonal complex (CC) 59 (32.7%), CC239 (29.7%), and CC5 (24.8%). Among HA isolates, a significant difference was also seen between community-onset and hospital-onset MRSA isolates in terms of the source of specimens, antibiotic susceptibility patterns, and molecular characteristics.CA-MRSA isolates from adults in northern Taiwan were genetically significantly different from HA isolates. The community clones, CC59, spread into hospitals.

Emergence of community-acquired methicillin-resistant Staphylococcus aureus in an Iranian referral paediatric hospital

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals has been changed in recent years due to the arrival of community-associated MRSA (CA-MRSA) strains into healthcare settings. The aim of this study is to investigate the distribution of staphylococcal cassette chromosome mec (SCCmec) type V as well as SCCmec IV subtypes, which have been associated with community-acquired infection among healthcare-associated MRSA (HA-MRSA) isolates. Antimicrobial susceptibility, SCCmec type, spa type and the presence of Panton-Valentine leukocidin (PVL) genes were determined for all HA-MRSA isolates in an Iranian referral hospital. In this study of 48 HA-MRSA isolates, 13 (27%), three (6.2%), five (10.4%) and one (2%) belonged to SCCmec subtypes IVa, IVb, IVc and IVd, respectively. Only two isolates (4.2%) belonged to SCCmec types V Notably, one isolate was found to harbour concurrent SCCmec subtypes IVb and IVd. MRSA containing SCCmec subtype IVb, IVc and IVd as well as type V isolates were all susceptible to chloramphenicol, clindamycin and rifampicin, while the sensitivity to these antibiotics was lower among MRSA containing SCCmec subtype IVa. The most frequently observed spa ttype was t037, accounting for 88% (22/25). Three other spa type was t002, t1816 and t4478. Large reservoirs of MRSA containing type IV subtypes and type V now exist in patients in this Iranian hospital. Therefore, effective infection control management in order to control the spread of CA-MRSA is highly recommended.

Comparative evaluation of MRSA nasal colonization epidemiology in the urban and rural secondary school community of Kurdistan, Iraq

BACKGROUND

To study the nasal carriage rate of Staphylococcus aureus (S. aureus) (including methicillin-resistant strains) in secondary school community of the urban and rural districts of the Kurdistan region of Iraq, a cross-sectional population based survey was carried out in the city Duhok and rural areas of Amedya, Akre and Zakho.

METHODS

Nasal swabs were obtained from nostrils of 509 students aged 14-23 years. Resistance to methicillin was assessed by Kirby-Bauer disk diffusion and agar dilution assay. Vancomycin sensitivity was also tested on Muller-Hinton agar.

RESULTS

It was found that the frequency of overall S. aureus nasal carriage (SANC) was 17.75% (90/509, CI95, 14.58-21.42%). In urban areas, the carriage rate was 20.59% (49/239, CI95, 15.64-26.29%), whereas it was 15.24% (41/270, CI95, 11.17-20.10%) in rural districts. The frequency of methicillin-resistant S. aureus (MRSA) among the isolated strains was found to be 2.04% (1/49) and 21.95% (9/41) in urban and rural areas respectively. It was found that in urban residents, the odd ratio (OR) of acquiring SANC was 1.44 (CI95, 0.91-2.27%) and risk ratio (RR) was at least 1.35 (CI95, 0.92-1.96%) while OR decreased to 0.12 (CI95, 0.01-0.96%) for MRSA carriage. Hence, the S. aureus carriage rate was higher in urban districts compared to rural areas while more MRSA were found in rural areas compared to urban districts. All studied strains were sensitive to vancomycin.

CONCLUSION

This study provided baseline information for S. aureus nasal colonization in the region. Also, it showed that living in rural areas increased the odds of MRSA colonization. More attention should be paid to control MRSA colonization in rural communities.

Frequency of methicillin-resistant Staphylococcus aureus nasal carriage in healthy children

BACKGROUND AND OBJECTIVE

The prevalence of community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) is increasing around the world. It involves healthy people and causes a variety of diseases.

MATERIAL AND METHODS

This cross sectional study was conducted from September 2010-June 2011 on children less than 14 years of Ahvaz, southwest Iran. The participants were selected with two staged cluster sampling. A sterile cotton nasal swab was used to collect the samples from the 864 participants. MRSA isolates were identifed by catalase and coagulase tests and 1 μg oxacillin disk method. Polymerase chain reaction (PCR) was performed on all the MRSA colonies to detect the mecA gene. Data was put in SPSS 16 software and descriptive statistics and chi-square test were used for analysis.

RESULTS

Out of 864 children, 471 (54.51%) were male and 393 (45.49%) were female. 235 children (27.1%) had Staphylococcus aureus and 11 (1.3%) of all children diagnosed with MRSA. PCR showed that 7 colonies (0.8%) had the mecA gene.

CONCLUSION

The results of this study indicate that MRSA exists in healthy children of Ahvaz. Although the prevalence of CA-MRSA is lower than many other regions, it still needs close attention to prevent its transmission. Further studies are needed to identify the risk factors of CA-MRSA.

New epidemiology of Staphylococcus aureus infection in Asia

Not only is Asia the most populous region in the world, but inappropriate therapy, including self-medication with over-the-counter antimicrobial agents, is a common response to infectious diseases. The high antibiotic selective pressure among the overcrowded inhabitants creates an environment that is suitable for the rapid development and efficient spread of numerous multidrug-resistant pathogens. Indeed, Asia is among the regions with the highest prevalence rates of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) and community-associated methicillin-resistant S. aureus (CA-MRSA) in the world. Most hospitals in Asia are endemic for multidrug-resistant methicillin-resistant S. aureus (MRSA), with an estimated proportion from 28% (in Hong Kong and Indonesia) to >70% (in Korea) among all clinical S. aureus isolates in the early 2010s. Isolates with reduced susceptibility or a high level of resistance to glycopeptides have also been increasingly identified in the past few years. In contrast, the proportion of MRSA among community-associated S. aureus infections in Asian countries varies markedly, from <5% to >35%. Two pandemic HA-MRSA clones, namely multilocus sequence type (ST) 239 and ST5, are disseminated internationally in Asia, whereas the molecular epidemiology of CA-MRSA in Asia is characterized by clonal heterogeneity, similar to that in Europe. In this review, the epidemiology of S. aureus in both healthcare facilities and communities in Asia is addressed, with an emphasis on the prevalence, clonal structure and antibiotic resistant profiles of the MRSA strains. The novel MRSA strains from livestock animals have been considered to constitute a public health threat in western countries. The emerging livestock-associated MRSA strains in Asia are also included in this review.

Effect of mupirocin decolonization on subsequent methicillin-resistant Staphylococcus aureus infection in infants in neonatal intensive care units

OBJECTIVE

To evaluate whether topical mupirocin treatment can effectively decolonize methicillin-resistant Staphylococcus aureus (MRSA) carriage and reduce subsequent MRSA infection in neonates.

METHODS

During a 1-year period, the infants admitted to our neonatal intensive care units (NICUs)-1 and NICU-2 were included, and specimens from the nares and umbilicus were obtained within 24 hours, and specimen collection was repeated weekly for 2 weeks. Mupirocin was administered for 5 days to the infants with MRSA colonization in NICU-1 during the first half of the year and then switched to those in NICU-2 during the second half of the year.

RESULTS

A total of 525 infants were recruited: 257 infants in the treatment group and 268 in the control group. MRSA colonization was detected in 130 infants (25%) during NICU stay, which is a similar rate in both groups. Twenty-two (4.2%) episodes of MRSA infection were identified. The rate of MRSA infection was significantly higher in infants with prior colonization than in those without (10.2% vs. 2.3%, P<0.001). Among the infants with prior colonization, the rate of MRSA infection in the treatment group was significantly lower than that in the control group (3.2% vs. 16%, P=0.014), and the rate in the treatment group was comparable to that in those without colonization (P=0.7804). Of the 15 infants with both clinical and colonizing isolates, indistinguishable strains between the paired isolates from the same infant by molecular methods were identified in 14 infants (93%).

CONCLUSION

Administering mupirocin topical therapy to MRSA-colonized infants in NICUs might reduce subsequent MRSA infections during hospitalization in these infants. A large-scale study should be conducted.

Nasal carriage of methicillin-resistant Staphylococcus aureus during the first 2 years of life in children in northern Taiwan

BACKGROUND

Most reported studies of methicillin-resistant Staphylococcus aureus (MRSA) carriage have represented 1 time point. To better understand dynamic changes of nasal MRSA carriage, we conducted this longitudinal study in Taiwan.

METHODS

We recruited 304 newborn babies and obtained samples from nares for detection of S. aureus within 3 days of life, and obtained further samples periodically up to 2 years of age. A total of 12 samplings were attempted to be obtained.

RESULTS

Totally, 273 subjects with ≥9 samples were included for analysis. One hundred and ten subjects (40%) harbored MRSA, on one or more occasions; of these 82 (75%) had ≥2 positive specimens and 84 (76%) had colonization ≤4 months of age. Fourteen infants (5.1%) carried MRSA within 3 days of life, the rate peaked at the age of 2 months (21%) and it was lowest (3.1%) at the age of 18 months. All but 4 first MRSA isolates from the colonized subjects carried either staphylococcal cassette chromosome (SCCmec) IV or V(T). Of 32 subjects with ≥4 MRSA isolates, all isolates from the same subject were genetically indistinguishable in 17 (53%) and genetically related in an additional 9 (28%). Five episodes of skin and soft tissue infections (SSTIs) were identified in 4 subjects.

CONCLUSION

In Taiwan, during the first 2 years of life, two-fifths of the children ever harbored MRSA, whereas fewer than 2% of them had SSTIs. Three-fourths of the colonization occurred within the first 4 months and were persistent. More than half of the persistent colonizing isolates were genetically indistinguishable.

Staphylococcus aureus spa type t437: identification of the most dominant community-associated clone from Asia across Europe

Methicillin-resistant Staphylococcus aureus (MRSA) belonging to the multilocus sequence type clonal complex 59 (MLST CC59) is the predominant community-associated MRSA clone in Asia. This clone, which is primarily linked with the spa type t437, has so far only been reported in low numbers among large epidemiological studies in Europe. Nevertheless, the overall numbers identified in some Northern European reference laboratories have increased during the past decade. To determine whether the S. aureus t437 clone is present in other European countries, and to assess its genetic diversity across Europe, we analysed 147 S. aureus t437 isolates from 11 European countries collected over a period of 11 years using multiple locus variable number tandem repeat fingerprinting/analysis (MLVF/MLVA) and MLST. Additionally 16 S. aureus t437 isolates from healthy carriers and patients from China were included. Most isolates were shown to be monophyletic with 98% of the isolates belonging to the single MLVA complex 621, to which nearly all included isolates from China also belonged. More importantly, all MLST-typed isolates belonged to CC59. Our study implies that the European S. aureus t437 population represents a genetically tight cluster, irrespective of the year, country and site of isolation. This underpins the view that S. aureus CC59 has been introduced into several European countries, not being restricted to particular geographical regions or specific host environments. The European S. aureus t437 isolates thus bear the general hallmarks of a high-risk clone.

Nasal Carriage and Resistance Pattern of Multidrug Resistant Staphylococcus aureus Among Healthy Children in Kashan, Iran

Background:

Nasal carriage of Staphylococcus aureus is a substantial source of human infections. Detection and treatment of nasal carriage in children with methicillin-resistant and multidrug resistant S. aureus (MRSA and MDRSA, respectively) may be an important modality in prevention of infections.

Objectives:

This study determined the prevalence, antibiotic resistance patterns and risk factors for nasal carriage of MDRSA among healthy children.

Patients and Methods:

This cross-sectional study was carried out on 350 one-month to 14-year-old healthy children in Kashan city, Iran. From all health-care centers, four were chosen by simple random sampling. Nasal samples were cultured in blood agar medium for S. aureus and antibiotic susceptibility profile was determined by disc diffusion and E-test. Risk factors for nasal carriage of MDRSA were also determined.

Results:

A total of 92 (26.3%) S. aureus isolates were obtained, of which 33 (35.9%) were MRSA and 27 (29.3%) were MDRSA. Of MRSA strains, 19 (70.4%) were MDRSA. S. aureus isolates showed 52.2% resistance to cephalothin, 33.7% to co-trimoxazole, 26.1% to clindamycin, 26.1% to ciprofloxacin, 4.3% to vancomycin, and 35.9% to oxacillin. The risk factors for nasal carriage of MDRSA were antibiotic usage during the last three months (P = 0.006), family size of more than four members (P = 0.044), and parental smoking (P = 0.045).

Conclusions:

MDRSA was not uncommon among healthy children in Kashan and prevention of its spread in the population is judicious.

Risk Factors for Methicillin Resistant Staphylococcus aureus Nasal Colonization of Healthy Children

Background:

Nasal colonization of healthy children with Staphylococcus aureus is an important risk factor for different infections. Detection of colonized individuals with methicillin resistant S. aureus (MRSA) and its eradication is the proper prevention strategy for infection spread in the community and health-care centers.

Objectives:

The aim of this study was to determine the prevalence, associated risk factors and antibiotic resistance pattern among healthy children who were nasal carriers of S. aureus.

Patients and Methods:

This cross-sectional study was conducted on 350 one month to 14-year-old healthy children living in Kashan/Iran. The nasal specimens were cultured in blood agar medium for S. aureus. Positive cultures were evaluated for cephalothin, co-trimoxazole, clindamycin, ciprofloxacin, oxacillin and vancomycin susceptibility by the disc diffusion method and E-test. Risk factors for nasal carriage of S. aureus and MRSA were evaluated.

Results:

Frequency of S. aureus nasal carriage was 92 from 350 cases (26.2%), amongst which 33 (35.9%) were MRSA. Isolates indicated an overall resistance of 52.2% to cephalothin, 33.7% to co-trimoxazol, 26.1% to ciprofloxacin, 26.1% to clindamycin, 35.9% to oxacillin and 4.3% to vancomycin. Factors associated with MRSA nasal carriage included gender (P value 0.001), age of less than four years (P value 0.016), number of individuals in the family (P value < 0.001), antibiotic use (P value < 0.001) and admission (P value < 0.001) during the previous three months, parental smoking (P value < 0.001) and sleeping with parents (P value 0.022).

Conclusions:

Age of less than four years, male sex, family size being more than four, antibiotic use and admission during the previous three months, parental smoking and sleeping with parents were independent risk factors for nasal colonization with MRSA.

Differences in epidemiological and molecular characteristics of nasal colonization with Staphylococcus aureus (MSSA-MRSA) in children from a university hospital and day care centers

Background

Clinical significance of Staphylococcus aureus colonization has been demonstrated in hospital settings; however, studies in the community have shown contrasting results regarding the relevance of colonization in infection by community-associated MRSA (CA-MRSA). In Colombia there are few studies on S. aureus colonization. The aim of this study was to determine the molecular and epidemiological characteristics of nasal colonization by S. aureus (MSSA-MRSA) in children from a university hospital and day care centers (DCCs) of Medellin, Colombia.

Methods

An observational cross-sectional study was conducted in 400 children (200 in each setting), aged 0 months to 5 years, during 2011. Samples were collected from each nostril and epidemiological information was obtained from the parents. Genotypic analysis included spa typing, PFGE, MLST, SCCmec typing, detection of genes for virulence factors and agr groups.

Results

Frequency of S. aureus colonization was 39.8% (n = 159) (hospital 44.5% and DCCs 35.0%) and by MRSA, 5.3% (n = 21) (hospital 7.0% and DCCs 3.5%). Most S. aureus colonized children were older than two years (p = 0.005), the majority of them boys (59.1%), shared a bedroom with a large number of people (p = 0.028), with history of β-Lactamase inhibitors usage (p = 0.020). MSSA strains presented the greatest genotypic diversity with 15 clonal complexes (CC). MRSA isolates presented 6 CC, most of them (47.6%) belonged to CC8-SCCmec IVc and were genetically related to previously reported infectious MRSA strains.

Conclusion

Differences in epidemiological and molecular characteristics between populations may be useful for the understanding of S. aureus nasal colonization dynamics and for the design of strategies to prevent S. aureus infection and dissemination. The finding of colonizing MRSA with similar molecular characteristics of those causing infection demonstrates the dissemination capacity of S. aureus and the risk of infection among the child population.

Does Staphylococcus aureus nasal carriage require eradication prior to elective ambulatory surgery in children?

PURPOSE

Rates of community-associated Staphylococcus aureus, and particularly of methicillin-resistant Staphylococcus aureus (MRSA) in children, have increased in recent years. We investigated rates of nasal colonization of S. aureus, and a possible correlation between nasal carriage and wound infection.

METHODS

A prospective study of children scheduled for elective day-care surgical procedures between January 2008 and December 2012 at one medical center. Nasal swabs were taken before surgery, and follow-up was performed 1-2 weeks following surgery.

RESULTS

Of 1,127 children (median age 2 years, 70.6% males), positive nasal swabs were detected in 228 (20.2%). Rates of S. aureus nasal carriage were lowest for ages 6 months to 2 years and highest for ages 4-11 years. Child's sex did not associate with the risk for positive nasal swabs. Positive nasal swabs for MRSA were detected in five boys (0.62% of the population). Five children (0.44%) had wound infection. None of them was a nasal carrier.

CONCLUSIONS

No correlation was observed between positive nasal swabs and wound infection in children who were candidates for elective ambulatory operations. This suggests that evaluation of S. aureus nasal carriage and eradication may not be necessary in this population.

Nasal carriage of multi-drug resistant Panton-Valentine leucocidin-positive methicillin-resistant Staphylococcus aureus in children in Tripoli-Libya

Methicillin-resistant Staphylococcus aureus (MRSA) colonized children are at an increased risk of developing infections than methicillin-sensitive S. aureus colonized children. Nasal specimens from inpatient children, mothers of inpatient children, healthcare workers, and outpatient children at Tripoli Children Hospital (TCH) were examined for MRSA by chromogenic MRSA ID medium. Susceptibility of MRSA isolates to antibiotics was determined by the disc diffusion method. The nasal carriage rate of MRSA among inpatient children (8.3%, 24 of 289), their mothers (11%, 22 of 200), and healthcare workers (12.4%, 22 of 178) was significantly higher than among outpatient children (2.2%, 2 of 91) (P < 0.05, P < 0.02, and P < 0.006, respectively). Of the examined MRSA isolates (N = 35) 10 (28.6%) were positive for Panton-Valentine leucocidin genes by polymerase chain reaction. Multidrug resistance was found in 24.3% (17 of 70) of MRSA isolates. Nasal carriage of multidrug-resistant Panton-Valentine leucocidin-positive MRSA is not uncommon among inpatient children and their mothers in Tripoli.

Prevalence and molecular characterization of Staphylococcus aureus colonization among neonatal intensive care units in Taiwan

BACKGROUND

Staphylococcus aureus, particularly methicillin-resistant (MRSA), is an important pathogen in neonatal intensive care units (NICUs). Carriage of S. aureus is a significant risk factor for subsequent infection.

OBJECTIVES

To determine the current status of MRSA prevalence among NICU-hospitalized infants in Taiwan, we conducted this pilot island-wide survey.

METHODS

On two designated dates in 2011, each patient who stayed in the NICUs of 7 participating hospitals was included. Nasal and umbilical swabs were obtained and sent for detection of S. aureus. The prevalence and risk factors for MRSA carriage were analyzed. MRSA strains were tested for antimicrobial susceptibility and underwent molecular characterization.

RESULTS

A total of 251 subjects were included. The overall prevalence of S. aureus and MRSA carriage was 13 and 4.4%, respectively. Previous skin and soft tissue infection was the only predictor in multivariate analysis (OR 40.36; 95% CI 2.32-702.64; p = 0.011). Among 11 MRSA isolates, 3 pulsotypes were identified, with one major type (73%). Nine isolates carried a type IV staphylococcal chromosomal cassette, and 2 carried the type VT. All but one MRSA isolate belonged to linage sequence type 59, the community clone in Taiwan.

CONCLUSIONS

On a designated date, 4.4% of the infants staying in NICUs in Taiwan carried almost genetically identical community strains of MRSA. MRSA colonization in these infants was significantly associated with previous skin and soft tissue infection.

Methicillin-resistant Staphylococcus aureus nasal carriage in neonates and children attending a pediatric outpatient clinics in Brazil

Background

In Latin America, few studies have been carried out on methicillin-resistant Staphylococcus aureus carriage in the pediatric population. We conducted a survey of nasal S. aureus carriage in neonates and in children attending the pediatric outpatient clinics in a large Brazilian city with high antimicrobial consumption.

Methods

Pernasal swabs of neonates were collected upon admission and at discharge in four neonatal intensive care units and of children less than five years of age during outpatient visits. Methicillin-resistant S. aureus isolates were characterized for antibiotic susceptibility, mec gene presence, pulsed-field gel electrophoresis, spa type, SCCmec-type, multilocus sequence type, and presence of Panton-Valentine leukocidin genes.

Results

S. aureus was carried by 9.1% and 20.1% of the 701 neonates and of 2034 children attending the outpatient clinics, respectively; methicillin-resistant S. aureus carriage was detected in 0.6% and 0.2%, of the these populations, respectively. Healthcare-associated methicillin-resistant S. aureus strains found in neonates from neonatal intensive care units and outpatients were genetically related to the Brazilian (SCCmec-III, ST239) and to the Pediatric (SCCmec-IV, ST5) clones. Community-associated methicillin-resistant S. aureus was only detected in outpatients. None of the methicillin-resistant S. aureus strains contained the Panton-Valentine leukocidin gene. Methicillin-resistant S. aureus strains related to the Brazilian clone showed multidrug resistance pattern.

Conclusions

Despite the high antibiotic pressure in our area, and the cross transmission of the healthcare-associated methicillin-resistant S. aureus clones between neonatal intensive care units and outpatients, the prevalence of methicillin-resistant S. aureus carriage is still low in our setting.

Characterization and comparison of 2 distinct epidemic community-associated methicillin-resistant Staphylococcus aureus clones of ST59 lineage

Sequence type (ST) 59 is an epidemic lineage of community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) isolates. Taiwanese CA-MRSA isolates belong to ST59 and can be grouped into 2 distinct clones, a virulent Taiwan clone and a commensal Asian-Pacific clone. The Taiwan clone carries the Panton–Valentine leukocidin (PVL) genes and the staphylococcal chromosomal cassette mec (SCCmec) V_T, and is frequently isolated from patients with severe disease. The Asian-Pacific clone is PVL-negative, carries SCCmec IV, and a frequent colonizer of healthy children. Isolates of both clones were characterized by their ability to adhere to respiratory A549 cells, cytotoxicity to human neutrophils, and nasal colonization of a murine and murine sepsis models. Genome variation was determined by polymerase chain reaction of selected virulence factors and by multi-strain whole genome microarray. Additionally, the expression of selected factors was compared between the 2 clones. The Taiwan clone showed a much higher cytotoxicity to the human neutrophils and caused more severe septic infections with a high mortality rate in the murine model. The clones were indistinguishable in their adhesion to A549 cells and persistence of murine nasal colonization. The microarray data revealed that the Taiwan clone had lost the ø3-prophage that integrates into the β-hemolysin gene and includes staphylokinase- and enterotoxin P-encoding genes, but had retained the genes for human immune evasion, scn and chps. Production of the virulence factors did not differ significantly in the 2 clonal groups, although more α-toxin was expressed in Taiwan clone isolates from pneumonia patients. In conclusion, the Taiwan CA-MRSA clone was distinguished by enhanced virulence in both humans and an animal infection model. The evolutionary acquisition of PVL, the higher expression of α-toxin, and possibly the loss of a large portion of the β-hemolysin-converting prophage likely contribute to its higher pathogenic potential than the Asian-Pacific clone.

Major characteristics of Staphylococcus aureus colonizing Jordanian infants

BACKGROUND

Colonization of infants with methicillin-resistant Staphylococcus aureus (MRSA) carries specific toxin genes. In particular, Panton-Valentine leukocidin (PVL) are a risk factor for subsequent infection during hospitalization. This prospective study investigated important epidemiological characteristics of Staphylococcus aureus colonizing the nares and intestines of Jordanian infants.

METHODS

A total of 860 nasal and stool specimens were obtained from each of the 430 infants admitted to the neonatal intensive care unit or referred to outpatient clinics of Jordan University Hospital. All specimens were cultured to recover S. aureus, all isolates were tested for antimicrobial susceptibility and the MRSA strains for presence of specific toxin genes and SCCmec using polymerase chain reaction.

RESULTS

Eighty of the 430 (18.6%) infants were colonized with S. aureus, of these, 27 (6.3%) harbored the organism in both the nose and intestine. The frequency of S. aureus nasal and intestinal carriage in outpatient infants compared to inpatients admitted to the neonatal intensive care unit was significantly higher (27.3% vs 2.8%) and (17.1% vs 2.3%), respectively. MRSA accounted for 57/107 (53.3%) of all isolates, and of these 16/57 (28%) were PVL-positive and carried SCCmec type IV, except one, which was type III. All nasal and intestinal MRSA carried at least one toxin gene (tst, eta, seb), but few carried two toxin genes.

CONCLUSION

This study demonstrates that S. aureus strains are more frequently colonizing Jordanian outpatient infants than inpatients and all MRSA strains carried 1-3 clinically important staphylococcal toxin genes. Further studies are needed to investigate the role of these toxins in hospitalized infants.

MRSA nasal colonization in children: prevalence meta-analysis, review of risk factors and molecular genetics

BACKGROUND

We report a meta-analysis of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization prevalence in children and a review of the risk factors as well as molecular genetic characterization.

METHODS

All relevant studies reporting prevalence data on MRSA nasal colonization in children published between January 2000 and August 2010 were retrieved from the MEDLINE database and analyzed.

RESULTS

After screening 544 studies, 50 studies were included. We obtained an estimate of MRSA prevalence of 2.7% (95% confidence interval [CI]: 2.2-3.1); of 5.2% (95% CI: 3.1-7.3) in children with underlying conditions and of 2.3% (95% CI: 1.8-2.7) in healthy children; 5.4% (95% CI: 3.1-7.7) in children recruited in hospitals and 3% (95% CI: 2.4-3.6) in children recruited in the community. Staphylococcal cassette chromosome mec type IV is the most diffused cassette globally.

CONCLUSION

The hospital remains the environment where the microorganism circulates most. Children with underlying conditions could act as vectors of microorganisms between the hospital and the community. MRSA prevention strategies should be tailored to each specific institution, taking into account the nosocomial prevalence of MRSA nasal colonization and infections, and the prevalence of nasal colonization in the community that refers to the specific health care center.

A cluster of methicillin-sensitive Staphylococcus aureus colonization in a nursery

BACKGROUND

Staphylococcus aureus is among the most important pathogens of bacteremia in hospitals. Colonizing strains may spread to other patients.

METHODS

Ninety-two mothers visiting delivery rooms were included in this study. From the mothers, specimens were obtained from the nares and vagina for the detection of S. aureus. From the babies, specimens were obtained from the nares and umbilicus within 24 h in the nursery.

RESULTS

The carriage rates of S. aureus were 25% in the parturient mothers and 30.9% in their babies. The majority (55 isolates, 94.8%) of the isolates were methicillin-sensitive S. aureus (MSSA). Of the 55 MSSA isolates, 11 genotypes were identified for isolates from the mothers and five geno-types for isolates from the infants. A major clone was identified and accounted for 82% of 34 isolates from the babies. Nine pairs of mothers and babies were colonized with MSSA; by molecular methods, the paired isolates were indistinguishable in two pairs.

CONCLUSION

Newborn babies acquire S. aureus colonization soon after birth, partly from their mothers. Once S. aureus is introduced into a nursery, spread of the strain may occur if health-care workers do not execute infection control measures strictly.

Clinical spectrum of acute rhinosinusitis among atopic and nonatopic children in Taiwan

BACKGROUND

Rhinitis and sinusitis are very common medical conditions and have been shown to be frequently associated. The role of allergies in the pathogenesis of chronic rhinosinusitis has been confirmed; however, the role of allergies in acute rhinosinusitis is debatable. Nonetheless, allergies are an important factor in the development of rhinosinusitis.

OBJECTIVE

To evaluate the incidence of allergic rhinitis in patients with acute rhinosinusitis and identify the clinical spectrum in Taiwan.

METHODS

This study randomly recruited 69 participants between 3 and 12 years of age with acute rhinosinusitis over the period of one and a half years. All participants underwent a nasal peak expiratory flow rate (nPEFR) test, skin-Prick test (SPT), nasal smear examination, nasal culture, radiography (Water's projection) and were requested to complete the Pediatric Rhinoconjunctivitis Quality of Life Questionnaire (PRQLQ) as well as provide their allergic history.

RESULTS

Among the 69 participants in the study, 27 (39.1%) participants were shown to have allergic rhinitis. The most troublesome symptoms among the 69 participants with acute rhinosinusitis were postnasal drip (3.00 ± 1.29), nasal obstruction (2.94 ± 1.39) and cough (2.67 ± 1.42). The most troublesome symptoms among the 27 participants with acute rhinosinusitis combined with allergic rhinitis were nasal obstruction (3.33 ± 1.24), postnasal drip (3.22 ± 1.09) and itchy eyes (2.74 ± 1.43) and with the higher values. In addition, the participants (≧ 6 y/o) with acute rhinosinusitis combined with allergic rhinitis had significantly lower nPEFR values compared with the nonatopic children (75.2 ± 18.2 vs 96.6 ± 21.4, p<0.05). If nPEFR is below 75 mL/min, the positive predict value in the patients of acute rhinosinusitis is 75.0% combined with allergic rhinitis (sensitivity 63.2%; specificity 85.7%). Streptococcus pneumoniae (29.0%), Haemophilus influenzae (20.3%), and Moraxella catarrhalis (17.4%) were the major isolated pathogens in this study. The prevalence of colonization with Staphylococcus aureus in the 69 participants with acute rhinosinusitis was 23.2%, and 15.9% for methicillin-resistant S. aureus (MRSA).

CONCLUSION

This study demonstrated that the bacteriological properties of acute rhinosinusitis among children in Taiwan are the same as those in other parts of the world; however, the prevalence of colonization by MRSA was higher than among healthy children. Second, atopic children were more likely to develop acute rhinosinusitis than nonatopic children. Third, most Taiwanese children with acute rhinosinusitis complained of postnasal drip, nasal obstruction and cough. If a child suffering from acute rhinosinusitis complained of severe nasal obstruction (nPEFR≦75 mL/min), the doctor should be alerted to atopic conditions requiring further treatment. The issues dealt with in this study may require further research with a larger sample population over an extended period of time to verify these conclusions.

Molecular characterization and antimicrobial susceptibility of nasal Staphylococcus aureus isolates from a Chinese medical college campus

Staphylococcus aureus colonization and infection occur more commonly among persons living or working in crowded conditions, but characterization of S. aureus colonization within medical communities in China is lacking. A total of 144 (15.4%, 144/935) S. aureus isolates, including 28 (3.0%, 28/935) MRSA isolates, were recovered from the nares of 935 healthy human volunteers residing on a Chinese medical college campus. All S. aureus isolates were susceptible to vancomycin, quinupristin/dalfopristin and linezolid but the majority were resistant to penicillin (96.5%), ampicillin/sulbactam (83.3%) and trimethoprim/sulfamethoxazole (93.1%). 82%, (23/28) of the MRSA isolates and 66% (77/116) of the MSSA isolates were resistant to multiple antibiotics, and 3 MRSA isolates were resistant to mupirocin—an agent commonly used for nasal decolonization. 16 different sequence types (STs), as well as SCCmec genes II, III, IVd, and V, were represented among MRSA isolates. We also identified, for the first time, two novel STs (ST1778 and ST1779) and 5 novel spa types for MRSA. MRSA isolates were distributed in different sporadic clones, and ST59-MRSA-VId- t437 was found within 3 MRSA isolates. Moreover, one isolate with multidrug resistance belonging to ST398-MRSA-V- t571 associated with animal infections was identified, and 3 isolates distributed in three different clones harbored PVL genes. Collectively, these data indicate a high prevalence of nasal MRSA carriage and molecular heterogeneity of S. aureus isolates among persons residing on a Chinese medical college campus. Identification of epidemic MRSA clones associated with community infection supports the need for more effective infection control measures to reduce nasal carriage and prevent dissemination of MRSA to hospitalized patients and health care workers in this community.

Neutrophils in innate host defense against Staphylococcus aureus infections

Staphylococcus aureus has been an important human pathogen throughout history and is currently a leading cause of bacterial infections worldwide. S. aureus has the unique ability to cause a continuum of diseases, ranging from minor skin infections to fatal necrotizing pneumonia. Moreover, the emergence of highly virulent, drug-resistant strains such as methicillin-resistant S. aureus in both healthcare and community settings is a major therapeutic concern. Neutrophils are the most prominent cellular component of the innate immune system and provide an essential primary defense against bacterial pathogens such as S. aureus. Neutrophils are rapidly recruited to sites of infection where they bind and ingest invading S. aureus, and this process triggers potent oxidative and non-oxidative antimicrobial killing mechanisms that serve to limit pathogen survival and dissemination. S. aureus has evolved numerous mechanisms to evade host defense strategies employed by neutrophils, including the ability to modulate normal neutrophil turnover, a process critical to the resolution of acute inflammation. Here we provide an overview of the role of neutrophils in host defense against bacterial pathogens and discuss strategies employed by S. aureus to circumvent neutrophil function.

Retrospective study of necrotizing fasciitis and characterization of its associated methicillin-resistant Staphylococcus aureus in Taiwan

Background

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a prevalent pathogen of necrotizing fasciitis (NF) in Taiwan. A four-year NF cases and clinical and genetic differences between hospital acquired (HA)- and community-acquired (CA)-MRSA infection and isolates were investigated.

Methods

A retrospective study of 247 NF cases in 2004-2008 and antimicrobial susceptibilities, staphylococcal chromosomal cassette mec (SCCmec) types, pulsed field gel electrophoresis (PFGE) patterns, virulence factors, and multilocus sequence typing (MLST) of 16 NF-associated MRSA in 2008 were also evaluated.

Results

In 247 cases, 42 microbial species were identified. S. aureus was the major prevalent pathogen and MRSA accounted for 19.8% of NF cases. Most patients had many coexisting medical conditions, including diabetes mellitus, followed by hypertension, chronic azotemia and chronic hepatic disease in order of decreasing prevalence. Patients with MRSA infection tended to have more severe clinical outcomes in terms of amputation rate (p < 0.05) and reconstruction rate (p = 0.001) than those with methicillin-sensitive S. aureus or non-S. aureus infection. NF patients infected by HA-MRSA had a significantly higher amputation rate, comorbidity, C-reactive protein level, and involvement of lower extremity than those infected by CA-MRSA. In addition to over 90% of MRSA resistant to erythromycin and clindamycin, HA-MRSA was more resistant than CA-MRSA to trimethoprim-sulfamethoxazole (45.8% vs. 4%). ST59/pulsotype C/SCCmec IV and ST239/pulsotype A/SCCmec III isolates were the most prevalent CA- and HA-MRSA, respectively in 16 isolates obtained in 2008. In contrast to the gene for γ-hemolysin found in all MRSA, the gene for Panton-Valentine leukocidin was only identified in ST59 MRSA isolates. Other three virulence factors TSST-1, ETA, and ETB were occasionally identified in MRSA isolates tested.

Conclusion

NF patients with MRSA infection, especially HA-MRSA infection, had more severe clinical outcomes than those infected by other microbial. The prevalent NF-associated MRSA clones in Taiwan differed distinctly from the most predominant NF-associated USA300 CA-MRSA clone in the USA. Initial empiric antimicrobials with a broad coverage for MRSA should be considered in the treatment of NF patients in an endemic area.

Successful control of methicillin-resistant Staphylococcus aureus in endemic neonatal intensive care units--a 7-year campaign

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is among the most important nosocomial pathogens in the intensive care unit (ICU) worldwide, including Taiwan. Since 1997, our neonatal ICUs (NICUs) had become endemic for MRSA.

Methodology/Principal Findings

To control MRSA spread in our NICUs, we implemented a series of infection control measures stepwise, including reinforcement of hand hygiene since January 2000, augmentation of aseptic care over the insertion site of central venous catheter since July 2001, introduction of alcohol-based handrubs since April 2003, surveillance culture for MRSA and cohort care for the colonized patients between March 2003 and February 2004, and surveillance culture with subsequent decolonization of MRSA between August 2005 and July 2006. After implementation of these measures, MRSA healthcare-associated infection (HAI) density reduced by 92%, from 5.47 episodes per 1000 patient-days in 1999 to 0.45 episodes per 1000 patient-days in 2006; MRSA bloodstream infection reduced from 40 cases in 1999 to only one case in 2006. Compared to those obtained during the period of surveillance culture without decolonization, both rates of MRSA colonization (8.6% vs. 41%, p<0.001) and infection (1.1% vs. 12%, p<0.001) decreased significantly during the period of surveillance and decolonization. Molecular analysis of the clinical isolates during the study period showed that the endemic clone, which dominated between 1998 and 2005, almost disappeared in 2006, while the community clones increased significantly in 2006–2007.

Conclusion/Significance

Through infection control measures, MRSA HAIs can be successfully controlled, even in areas with high levels of endemic MRSA infections such as our NICUs.