Community-acquired methicillin-resistant Staphylococcus aureus among military recruits

Bacterial Genotype, Carrier Risk Factors, and an Antimicrobial Stewardship Approach Relevant To Methicillin-resistant Staphylococcus Aureus Prevalence in a Population of Macaques Housed in a Research Facility

Methicillin-resistant Staphylococcus aureus (MRSA) remains a significant problem for human and animal health and can negatively affect the health status of macaques and other nonhuman primates (NHP) in research colonies. However, few publications provide guidance on the prevalence, genotype, or risk factors for macaques with MRSA and even fewer on how to effectively respond to MRSA once identified in a population. After having a clinical case of MRSA in a rhesus macaque, we sought to determine the MRSA carrier prevalence, risk factors, and genotypes of MRSA in a population of research NHPs. Over a 6-wk period in 2015, we collected nasal swabs from 298 NHPs. MRSA was isolated from 28% (n = 83). We then reviewed each macaque's medical record for a variety of variables including animal housing room, sex, age, number of antibiotic courses, number of surgical interventions, and SIV status. Analysis of these data suggests that MRSA carriage is associated with the room location, age of the animal, SIV status, and the number of antibiotic courses. We used multilocus sequence typing and spa typing on a subset of MRSA and MSSA isolates to determine whether the MRSA present in NHPs was comparable with common human strains. Two MRSA sequence types were predominant: ST188 and a novel MRSA genotype, neither of which is a common human isolate in the United States. We subsequently implemented antimicrobial stewardship practices (significantly reducing antimicrobial use) and then resampled the colony in 2018 and found that MRSA carriage had fallen to 9% (26/285). These data suggest that, as in humans, macaques may have a high carrier status of MRSA despite low clinically apparent disease. Implementing strategic antimicrobial stewardship practices resulted in a marked reduction in MRSA carriage in the NHP colony, highlighting the importance of limiting antimicrobial use when possible.

Genomic Epidemiology Suggests Community Origins of Healthcare-Associated USA300 Methicillin-Resistant Staphylococcus aureus

BACKGROUND

Hospital-onset (HO) methicillin-resistant Staphylococcus aureus (MRSA) infections have declined over the past decade due to infection control strategies; community-onset (CO) and healthcare-associated community-onset (HACO) MRSA, particularly USA300, has declined less. We examined the role of community strains to explain the difference.

METHODS

We performed whole-genome sequencing (WGS) on MRSA clinical isolates from Cook County Health patients during 2011-2014. We defined infections as CO, HO, or HACO epidemiologically. We integrated genomic, community exposure, and statewide hospital discharge data to infer MRSA origin.

RESULTS

Among 1020 individuals with available WGS, most were USA300 wound infections (580 CO, 143 HO, 297 HACO). USA300 HO, CO, and HACO infections were intermixed on the USA300 phylogeny, consistent with common strains circulating across community and healthcare settings. Community exposures (eg, substance abuse, incarceration, homelessness) were associated with HACO and HO infections, and genetically linked individuals from both groups had little overlap in healthcare facilities, supporting community origins. Most repeat infections-over months to years-occurred in individuals persistently carrying their own strains. These individuals were more likely to have genetic linkages, suggesting a role of persistent colonization in transmission.

CONCLUSIONS

Efforts to reduce presumed nosocomial USA300 spread may require understanding and controlling community sources and transmission networks, particularly for repeat infections.

Nasal microbiota evolution within the congregate setting imposed by military training

The human microbiome is comprised of a complex and diverse community of organisms that is subject to dynamic changes over time. As such, cross-sectional studies of the microbiome provide a multitude of information for a specific body site at a particular time, but they fail to account for temporal changes in microbial constituents resulting from various factors. To address this shortcoming, longitudinal research studies of the human microbiome investigate the influence of various factors on the microbiome of individuals within a group or community setting. These studies are vital to address the effects of host and/or environmental factors on microbiome composition as well as the potential contribution of microbiome members during the course of an infection. The relationship between microbial constituents and disease development has been previously explored for skin and soft tissue infections (SSTIs) within congregate military trainees. Accordingly, approximately 25% of the population carries Staphylococcus aureus within their nasal cavity, and these colonized individuals are known to be at increased risk for SSTIs. To examine the evolution of the nasal microbiota of U.S. Army Infantry trainees, individuals were sampled longitudinally from their arrival at Fort Benning, Georgia, until completion of their training 90 days later. These samples were then processed to determine S. aureus colonization status and to profile the nasal microbiota using 16S rRNA gene-based methods. Microbiota stability differed dramatically among the individual trainees; some subjects exhibited great stability, some subjects showed gradual temporal changes and some subjects displayed a dramatic shift in nasal microbiota composition. Further analysis utilizing the available trainee metadata suggests that the major drivers of nasal microbiota stability may be S. aureus colonization status and geographic origin of the trainees. Nasal microbiota evolution within the congregate setting imposed by military training is a complex process that appears to be affected by numerous factors. This finding may indicate that future campaigns to prevent S. aureus colonization and future SSTIs among high-risk military trainees may require a ‘personalized’ approach.

Opportunities and Obstacles in the Prevention of Skin and Soft-Tissue Infections Among Military Personnel

INTRODUCTION

Skin and soft-tissue infections (SSTIs) are an important cause of infectious disease morbidity among military populations. Due to the high direct and indirect costs associated with SSTIs, particularly with methicillin-resistant Staphylococcus aureus (MRSA) infections, there remains a critical need for the development and evaluation of SSTI prevention strategies among high-risk military personnel. Herein, we review efforts of the Infectious Disease Clinical Research Program (IDCRP) related to the prevention of SSTIs in the military.

METHODS

The IDCRP of the Uniformed Services University has conducted clinical research protocols on SSTI epidemiology and prevention among military personnel since 2009. Observational studies have examined the epidemiology of Staphylococcus aureus colonization and SSTI in training and deployment settings. Two randomized controlled trials of personal hygiene strategies for SSTI prevention at Marine Corps Base Quantico (Virginia) and Fort Benning (Georgia) were performed. Lastly, two vaccine trials have been conducted by the IDCRP, including a Phase 2 S. aureus vaccine trial (currently ongoing) among military trainees.

RESULTS

Military recruits and deployed personnel experience an intense and prolonged exposure to S. aureus, the major causative agent of SSTI. The burden of S. aureus colonization and SSTI is particularly high in military trainees. Hygiene-based trials for S. aureus decolonization among military trainees were not effective in reducing rates of SSTI. In January 2018, the IDCRP initiated a Phase 2 S. aureus vaccine trial among the US Army Infantry training population at Fort Benning.

CONCLUSIONS

In the military, a disproportionate burden of SSTIs is borne by the recruit population. Strategies relying upon routine application of agents for S. aureus decolonization have not been effective in preventing SSTIs. A novel S. aureus vaccine candidate is being currently evaluated in a military training population and may represent a new opportunity to prevent SSTIs for the military.

Intersection of HIV and community-associated methicillin-resistant Staphylococcus aureus

The epidemiology of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has evolved over the past approximately 20 years, with certain populations appearing to have disproportionate risk. Of concern is the potential worsening of S. aureus infections in light of the continued opioid crisis. This review will discuss how CA-MRSA has significantly impacted HIV-infected individuals and address additional factors and populations that are associated with increased risk for MRSA. It will review therapeutic options and infection control strategies as well as highlight how whole genome sequencing can be used to extend traditional epidemiologic analysis and ultimately, inform infection prevention efforts. Continued work identifying those at the highest risk for MRSA, what the best infection prevention settings are in community settings and how to effectively implement and target these strategies is needed. Ultimately, infection control efforts will likely need to extend beyond healthcare settings to effectively and sustainably reduce MRSA infections.

Characterization of patients with bacteremia by methicillin-resistant Staphylococcus aureus in a high-complexity military hospital

Introduction: In Colombia, there are about 500,000 members in the national armed forces who consult military health institutions. In this population, methicillin-resistant Staphylococcus aureus (MRSA) has become a high-incidence pathogen. Objective: The aim of this study was to characterize patients with MRSA bacteremia in the Hospital Militar Central between 2012 and 2015. Materials and methods: This was an observational descriptive study with a retrospective review of clinical histories of hospitalized patients older than 18 years of age with positive blood cultures for methicillin-resistant S. aureus. The identification of the patients was made using the Whonet system, version 5.6. Results: From cultures positive for S. aureus, 24.8% were methicillin-resistant strains, with a higher prevalence in active military personnel. A similar frequency was observed for community-acquired MRSA bacteremias and those acquired at the hospital, with the community phenotype being the most frequent in both groups. The main infectious focus related to the development of bacteremia was soft tissue, followed by pulmonary tissue. There were higher complication rates in nosocomial bacteremias; 34.9% of the patients had prolonged stays attributable to complications triggered by the bacteremia. Conclusions: Active military personnel was the most affected population by MRSA, with a similar frequency in community-acquired and nosocomial bacteremias. The main infectious focus was soft tissue. Taking into account these data, studies that establish the prevalence of skin infections by MRSA should be carried out.

Life After USA300: The Rise and Fall of a Superbug

The community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) epidemic in the United States is largely attributable to the meteoric rise of a single clone, referred to as USA300. This strain not only spread across the United States in just a few years to become the predominant cause of staphylococcal disease, but it also appears to have increased the overall number of skin and soft-tissue infections (SSTIs), increasing the overall disease burden. While USA300 still constitutes a major public health burden, its prevalence may be decreasing in some parts of the United States. Other than an epidemic in South America due to a closely related strain, USA300 also seems to have been largely unable to establish itself as an endemic infection in other geographic locations. While there have been several hypotheses put forward to explain the enormous success of USA300, the reasons for its failures and its potential fall remain obscure. Far from being unique to USA300, the rise and fall of specific clones of S. aureus in human populations seems to be a common process that has occurred multiple times and in multiple locations. This review charts the rise of USA300 and the evidence that suggests that it may be in decline, and it considers how best to understand the future spread, containment, and possible extinction of CA-MRSA.

Safety and immunogenicity of a recombinant Staphylococcus aureus α-toxoid and a recombinant Panton-Valentine leukocidin subunit, in healthy adults

We conducted a randomized, double-blind, placebo-controlled dose-escalation study in healthy adults to evaluate the safety and immunogenicity of recombinant Staphylococcus aureus candidate vaccine antigens, recombinant α-toxoid (rAT) and a sub-unit of Panton-Valentine leukocidin (rLukS-PV). 176 subjects were enrolled and randomized within 1 of 11 treatment cohorts: monovalent rAT or rLukS-PV dosages of 10, 25, 50, and 100 μg; bivalent rAT:rLukS dosages of 10:10, 25:25, and 50:50 μg; and alum or saline placebo. All subjects were assessed at Days 0, 7, 14, 28, and 84. Subjects in the 50:50 μg bivalent cohort received a second injection on Day 84 and were assessed on Days 98 and 112. Incidence and severity of reactogenicity and adverse events (AEs) were compared. Geometric mean serum concentrations (GMC) and neutralizing activity of anti-rAT and anti-rLukS-PV IgG were assessed. Reactogenicity incidence was significantly higher in vaccine than placebo recipients (77% versus 55%, respectively; p = 0.006). However, 77% of reactogenicity events were mild and 19% were moderate in severity. The AE incidence and severity were similar between the cohorts. All monovalent and bivalent rAT dosages resulted in a significant increase in the anti-rAT IgG and anti- rLukS-PV GMCs between day 0 and 28 compared with placebo, and persisted through Day 84. Exploratory subgroup analyses suggested a higher GMC and neutralizing antibody titers for the 50 μg monovalent or bivalent rAT and rLukS-PV dose as compared to the other doses. No booster effect was observed after administration of the second dose. We conclude that the rAT and rLukS-PV vaccine formulations were well-tolerated and had a favorable immunogenicity profile, producing antibody with neutralizing activity through day 84. There was no benefit observed with a booster dose of the vaccine.

Bacterial Etiology and Risk Factors Associated with Cellulitis and Purulent Skin Abscesses in Military Trainees

Military trainees are at high risk for skin and soft-tissue infections (SSTIs). Although Staphylococcus aureus is associated with purulent SSTI, it is unclear to what degree this pathogen causes nonpurulent cellulitis. To inform effective prevention strategies and to provide novel insights into SSTI pathogenesis, we aimed to determine the etiology of SSTI in this population. We conducted a prospective observational study in US Army Infantry trainees with SSTI (cutaneous abscesses and cellulitis) from July 2012 through December 2014. We used standard microbiology, serology, and high-throughput sequencing to determine the etiology of SSTI. Furthermore, we compared purported risk factors as well as anatomic site colonization for S. aureus. Among 201 SSTI cases evaluated for SSTI risk factors, cellulitis was associated with lower extremity blisters (P = 0.01) and abscess was associated with methicillin-resistant S. aureus (MRSA) colonization (P<0.001). Among the 22 tested cellulitis cases that were part of the microbiome analysis, only 1 leading edge aspirate was culturable (Coagulase-negative Staphylococcus). Microbiome evaluation of aspirate specimens demonstrated that Rhodanobacter terrae was the most abundant species (66.8% average abundance), while abscesses were dominated by S. aureus (92.9% average abundance). Although abscesses and cellulitis share the spectrum of clinical SSTI, the bacterial etiologies as determined by current technology appear distinct. Furthermore, the presence of atypical bacteria within cellulitis aspirates may indicate novel mechanisms of cellulitis pathogenesis.

CLINICAL TRIALS REGISTRATION

NCT01105767.

Multi-Body-Site Microbiome and Culture Profiling of Military Trainees Suffering from Skin and Soft Tissue Infections at Fort Benning, Georgia

While it is evident that nasal colonization with S. aureus increases the likelihood of SSTI, there is a significant lack of information regarding the contribution of extranasal colonization to the overall risk of a subsequent SSTI. Furthermore, the impact of S. aureus colonization on bacterial community composition outside the nasal microbiota is unclear. Thus, this report represents the first investigation that utilized both culture and high-throughput sequencing techniques to analyze microbial dysbiosis at multiple body sites of healthy and diseased/colonized individuals. The results described here may be useful in the design of future methodologies to treat and prevent SSTIs.

Skin and soft tissue infections (SSTIs) are common in the general population, with increased prevalence among military trainees. Previous research has revealed numerous nasal microbial signatures that correlate with SSTI development and Staphylococcus aureus colonization. Thus, we hypothesized that the ecology of the inguinal, oropharynx, and perianal regions may also be altered in response to SSTI and/or S. aureus colonization. We collected body site samples from 46 military trainees with purulent abscess (SSTI group) as well as from 66 asymptomatic controls (non-SSTI group). We also collected abscess cavity samples to assess the microbial composition of these infections. Samples were analyzed by culture, and the microbial communities were characterized by high-throughput sequencing. We found that the nasal, inguinal, and perianal regions were similar in microbial composition and significantly differed from the oropharynx. We also observed differences in Anaerococcus and Streptococcus abundance between the SSTI and non-SSTI groups for the nasal and oropharyngeal regions, respectively. Furthermore, we detected community membership differences between the SSTI and non-SSTI groups for the nasal and inguinal sites. Compared to that of the other regions, the microbial compositions of the nares of S. aureus carriers and noncarriers were dramatically different; we noted an inverse correlation between the presence of Corynebacterium and the presence of Staphylococcus in the nares. This correlation was also observed for the inguinal region. Culture analysis revealed elevated methicillin-resistant S. aureus (MRSA) colonization levels for the SSTI group in the nasal and inguinal body sites. Together, these data suggest significant microbial variability in patients with SSTI as well as between S. aureus carriers and noncarriers.

IMPORTANCE While it is evident that nasal colonization with S. aureus increases the likelihood of SSTI, there is a significant lack of information regarding the contribution of extranasal colonization to the overall risk of a subsequent SSTI. Furthermore, the impact of S. aureus colonization on bacterial community composition outside the nasal microbiota is unclear. Thus, this report represents the first investigation that utilized both culture and high-throughput sequencing techniques to analyze microbial dysbiosis at multiple body sites of healthy and diseased/colonized individuals. The results described here may be useful in the design of future methodologies to treat and prevent SSTIs.

Methicillin-susceptible Staphylococcus aureus skin infections among military conscripts undergoing basic training in Bangkok, Thailand, in 2014

Background

Skin and soft tissue infections are common among military conscripts undergoing close-contact training activities. On June 4, 2014, an outbreak of Staphylococcus aureus skin infection was reported among military conscripts undergoing basic training in Bangkok, Thailand. An investigation was performed to verify the outbreak and recommend future prevention and control strategies.

Case presentation

The outbreak resulted in a rate of infection of 19.2 % and a fatality rate of 2.5 % (one death). All were Thai men aged 21.2 ± 1.0 years. Risk factors associated with infection were multiple erythematous papules and training in certain subunits. Randomly selected isolates were evaluated by pulsed field gel electrophoresis to confirm the clonal identity.

Conclusions

This report confirms that S. aureus skin infection can be fatal. Our study highlights the role of military personnel in the early detection, prompt treatment, and containment of outbreaks of skin infection, as well as other health issues among conscripts.

Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management

Staphylococcus aureus is a major human pathogen that causes a wide range of clinical infections. It is a leading cause of bacteremia and infective endocarditis as well as osteoarticular, skin and soft tissue, pleuropulmonary, and device-related infections. This review comprehensively covers the epidemiology, pathophysiology, clinical manifestations, and management of each of these clinical entities. The past 2 decades have witnessed two clear shifts in the epidemiology of S. aureus infections: first, a growing number of health care-associated infections, particularly seen in infective endocarditis and prosthetic device infections, and second, an epidemic of community-associated skin and soft tissue infections driven by strains with certain virulence factors and resistance to β-lactam antibiotics. In reviewing the literature to support management strategies for these clinical manifestations, we also highlight the paucity of high-quality evidence for many key clinical questions.

Community-associated methicillin-resistant Staphylococcus aureus: prevalence in skin and soft tissue infections at emergency departments in the Greater Toronto Area and associated risk factors

Objective:

Community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA), which is caused primarily by the Canadian methicillin-resistantStaphylococcus aureus-10 (CMRSA-10) strain (also known as the USA300 strain) has emerged rapidly in the United States and is now emerging in Canada. We assessed the prevalence, risk factors, microbiological characteristics and outcomes of CA-MRSA in patients with purulent skin and soft tissue infections (SSTIs) presenting to emergency departments (EDs) in the Greater Toronto Area.

Methods:

Patients withStaphylococcus aureusSSTIs who presented to 7 EDs between Mar. 1 and Jun. 30, 2007, were eligible for inclusion in this study. Antimicrobial susceptibilities and molecular characteristics of MRSA strains were identified. Demographic, risk factor and clinical data were collected through telephone interviews.

Results:

MRSA was isolated from 58 (19%) of 299 eligible patients. CMRSA-10 was identified at 6 of the 7 study sites and accounted for 29 (50%) of all cases of MRSA. Telephone interviews were completed for 161 of the eligible patients. Individuals with CMRSA-10 were younger (median 34 v. 63 yr,p= 0.002), less likely to report recent antibiotic use (22% v. 67%,p= 0.046) or health care–related risk factors (33% v. 72%,p= 0.097) and more likely to report community-related risk factors (56% v. 6%,p= 0.008) than patients with other MRSA strains. CMRSA-10 SSTIs were treated with incision and drainage (1 patient), antibiotic therapy (3 patients) or both (5 patients), and all resolved. CMRSA-10 isolates were susceptible to clindamycin, tetracycline and trimethoprimsulfamethoxazole.

Conclusion:

CA-MRSA is a significant cause of SSTIs in the Greater Toronto Area, and can affect patients without known community-related risk factors. The changing epidemiology of CA-MRSA necessitates further surveillance to inform prevention strategies and empiric treatment guidelines.

Prevalence of methicillin-resistant Staphylococcus aureus in skin and soft tissue infections in patients presenting to Canadian emergency departments

Background:

Community-associated methicillin-resistantStaphylococcus aureus(MRSA) is an increasingly common cause of skin and soft tissue infection (SSTI) worldwide. The prevalence of MRSA in SSTIs across Canada has not been well described. Studies in the United States have shown significant geographic variability in the prevalence of MRSA. This study characterizes the geographic prevalence and microbiology of MRSA in patients presenting to Canadian emergency departments with SSTIs.

Methods:

Using a prospective, observational design, we enrolled patients with acute purulent SSTIs presenting to 17 hospital emergency departments and 2 community health centres (spanning 6 Canadian provinces) between July 1, 2008, and April 30, 2009. Eligible patients were those whose wound cultures grewS. aureus. MRSA isolates were characterized by antimicrobial susceptibility testing and pulsed-field gel electrophoresis. All patients were subjected to a structured chart audit, and patients whose wound swabs grew MRSA were contacted by telephone to gather detailed information regarding risk factors for MRSA infection, history of illness, and outcomes.

Results:

Of the 1,353S. aureus–positive encounters recorded, 431 (32%) grew MRSA and 922 (68%) wounds grew methicillin-susceptibleS. aureus. We observed significant variation in both the prevalence of MRSA (11–100%) and the proportion of community-associated strains of MRSA (0– 100%) across our study sites, with a significantly higher prevalence of MRSA in western Canada.

Interpretation:

MRSA continues to emerge across Canada, and the prevalence of MRSA in SSTIs across Canada is variable and higher than previously expected.

USA300 Methicillin-Resistant Staphylococcus aureus Emerging as a Cause of Bloodstream Infections at Military Medical Centers

Background.

USA300 methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of skin and soft-tissue infection (SSTI) in military personnel. USA300 MRSA has emerged as an important cause of healthcare-associated bloodstream infection (BSI) in metropolitan centers.

Objective.

To determine the prevalence, risk factors, and patient outcomes associated with USA300 MRSA BSI in military tertiary medical centers.

Design.

Retrospective case-control study.

Patients.

Patients admitted during the period 2001–2009 with MRSA BSI.

Setting.

Walter Reed Army Medical Center (Washington, DC) and National Naval Medical Center (Bethesda, MD) tertiary medical centers with 500 inpatient beds combined, which provide care to active duty service members and military beneficiaries.

Methods.

After identifying patients with MRSA BSI, we collected epidemiological data from electronic medical records and characterized bacterial isolates using pulsed-field gel electrophoresis (PFGE).

Results.

A total of 245 MRSA BSI cases were identified, and 151 isolates were available for analysis. Epidemiological characteristics for the 151 patients with available isolates included the following: mean age, 61 years; male sex, 70%; white race, 62%; and combat-wounded service members, 11%. The crude in-hospital mortality rate was 17%. PFGE demonstrated that 30 (20%) of 151 MRSA BSI cases with isolates available for analysis were due to USA300, and 27 (87%) of these 30 cases were healthcare-associated infection. USA300 was associated with a significantly increasing proportion of MRSA BSI when examined over sequential time periods: 2 (4%) of 51 isolates during 2001–2003, 9 (19%) of 47 isolates during 2004–2006, and 19 (36%) of 53 isolates during 2007–2009 (P<.001).

Conclusion.

USA300 MRSA is emerging as a cause of healthcare-associated BSI in tertiary military medical centers.

Chlorhexidine-Impregnated Cloths to Prevent Skin and Soft-Tissue Infection in Marine Recruits: A Cluster-Randomized, Double-Blind, Controlled Effectiveness Trial

Background.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) causes skin and soft-tissue infection (SSTI) in military recruits.

Objective.

To evaluate the effectiveness of 2% Chlorhexidine gluconate (CHG)-impregnated cloths in reducing rates of SSTI and S. aureus colonization among military recruits.

Design.

A cluster-randomized (by platoon), double-blind, controlled effectiveness trial.

Setting.

Marine Officer Candidate School, Quantico, Virginia, 2007.

Participants.

Military recruits.

Intervention.

Application of CHG-impregnated or control (Comfort Bath; Sage) cloths applied over entire body thrice weekly.

Measurements.

Recruits were monitored daily for SSTI. Baseline and serial nasal and/or axillary swabs were collected to assess S. aureus colonization.

Results.

Of 1,562 subjects enrolled, 781 (from 23 platoons) underwent CHG-impregnated cloth application and 781 (from 21 platoons) underwent control cloth application. The rate of compliance (defined as application of 50% or more of wipes) at 2 weeks was similar (CHG group, 63%; control group, 67%) and decreased over the 6-week period. The mean 6-week SSTI rate in the CHG-impregnated cloth group was 0.094, compared with 0.071 in the control group (analysis of variance model rate difference, 0.025 ± 0.016; P = .14). At baseline, 43% of subjects were colonized with methicillin-susceptible S. aureus (MSSA), and 2.1% were colonized with MRSA. The mean incidence of colonization with MSSA was 50% and 61% (P = .026) and with MRSA was 2.6% and 6.0% (P = .034) for the CHG-impregnated and control cloth groups, respectively.

Conclusions.

CHG-impregnated cloths applied thrice weekly did not reduce rates of SSTI among recruits. S. aureus colonization rates increased in both groups but to a lesser extent in those assigned to the CHG-impregnated cloth Intervention. Antecedent S. aureus colonization was not a risk factor for SSTI. Additional studies are needed to identify effective measures for preventing SSTI among military recruits.

Clinical Trials Registration.

ClinicalTrials.gov identifier: NCT00475930.

Correlation between nasal microbiome composition and remote purulent skin and soft tissue infections

The incidence of skin and soft tissue infections (SSTIs) has increased dramatically over the past decade, resulting in significant morbidity in millions of otherwise healthy individuals worldwide. Certain groups, like military personnel, are at increased risk for SSTI development. Although nasal colonization with Staphylococcus aureus is an important risk factor for the development of SSTIs, it is not clear why some colonized individuals develop disease while others do not. Recent studies have revealed the importance of microbial diversity in human health. Therefore, we hypothesized that the nasal microbiome may provide valuable insight into SSTI development. To examine this hypothesis, we obtained anterior-naris samples from military trainees with cutaneous abscesses and from asymptomatic (non-SSTI) participants. We also obtained samples from within abscess cavities. Specimens were analyzed by culture, and the microbial community within each sample was characterized using a 16S sequencing-based approach. We collected specimens from 46 non-SSTI participants and from 40 participants with abscesses. We observed a significantly higher abundance of Proteobacteria in the anterior nares in non-SSTI participants (P < 0.0001) than in participants with abscesses. Additionally, we noted a significant inverse correlation between Corynebacterium spp. and S. aureus (P = 0.0001). The sensitivity of standard microbiological culture for abscesses was 71.4%. These data expand our knowledge of the complexity of the nasal and abscess microbiomes and potentially pave the way for novel therapeutic and prophylactic countermeasures against SSTI.

Multidrug-resistant and methicillin-resistant Staphylococcus aureus (MRSA) in hog slaughter and processing plant workers and their community in North Carolina (USA)

BACKGROUND

Use of antimicrobials in industrial food-animal production is associated with the presence of antimicrobial-resistant Staphylococcus aureus (S. aureus) among animals and humans. Hog slaughter/processing plants process large numbers of animals from industrial animal operations and are environments conducive to the exchange of bacteria between animals and workers.

OBJECTIVES

We compared the prevalence of multidrug-resistant S. aureus (MDRSA) and methicillin-resistant S. aureus (MRSA) carriage among processing plant workers, their household members, and community residents.

METHODS

We conducted a cross-sectional study of hog slaughter/processing plant workers, their household members, and community residents in North Carolina. Participants responded to a questionnaire and provided a nasal swab. Swabs were tested for S. aureus, and isolates were tested for antimicrobial susceptibility and subjected to multilocus sequence typing.

RESULTS

The prevalence of S. aureus was 21.6%, 30.2%, and 22.5% among 162 workers, 63 household members, and 111 community residents, respectively. The overall prevalence of MDRSA and MRSA tested by disk diffusion was 6.9% and 4.8%, respectively. The adjusted prevalence of MDRSA among workers was 1.96 times (95% CI: 0.71, 5.45) the prevalence in community residents. The adjusted average number of antimicrobial classes to which S. aureus isolates from workers were resistant was 2.54 times (95% CI: 1.16, 5.56) the number among isolates from community residents. We identified two MDRSA isolates and one MRSA isolate from workers as sequence type 398, a type associated with exposure to livestock.

CONCLUSIONS

Although the prevalence of S. aureus and MRSA was similar in hog slaughter/processing plant workers and their household and community members, S. aureus isolates from workers were resistant to a greater number of antimicrobial classes. These findings may be related to the nontherapeutic use of antimicrobials in food-animal production.

Prospective multicenter study of community-associated skin and skin structure infections due to methicillin-resistant Staphylococcus aureus in Buenos Aires, Argentina

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is now the most common cause of skin and skin structure infections (SSSI) in several world regions. In Argentina prospective, multicenter clinical studies have only been conducted in pediatric populations.

OBJECTIVE

PRIMARY: describe the prevalence, clinical and demographic characteristics of adult patients with community acquired SSSI due to MRSA; secondary: molecular evaluation of CA-MRSA strains. Patients with MRSA were compared to those without MRSA.

MATERIALS AND METHODS

Prospective, observational, multicenter, epidemiologic study, with molecular analysis, conducted at 19 sites in Argentina (18 in Buenos Aires) between March 2010 and October 2011. Patients were included if they were ≥ 14 years, were diagnosed with SSSI, a culture was obtained, and there had no significant healthcare contact identified. A logistic regression model was used to identify factors associated with CA-MRSA. Pulse field types, SCCmec, and PVL status were also determined.

RESULTS

A total of 311 patients were included. CA-MRSA was isolated in 70% (218/311) of patients. Clinical variables independently associated with CA-MRSA were: presence of purulent lesion (OR 3.29; 95%CI 1.67, 6.49) and age <50 years (OR 2.39; 95%CI 1.22, 4.70). The vast majority of CA-MRSA strains causing SSSI carried PVL genes (95%) and were SCCmec type IV. The sequence type CA-MRSA ST30 spa t019 was the predominant clone.

CONCLUSIONS

CA-MRSA is now the most common cause of SSSI in our adult patients without healthcare contact. ST30, SCCmec IV, PVL+, spa t019 is the predominant clone in Buenos Aires, Argentina.

Prospective Analysis Methicillin-resistant Staphylococcus aureus and its Risk Factors

Background:

Since the early nineties, a new methicillin-resistant Staphylococcus aureus (MRSA) has existed in a form correlating with community health personnel. Community-acquired MRSA (CA-MRSA) could be differentiated from healthcare-associated MRSA (HA-MRSA) microbiologically, epidemiologically, and molecularly.

Aims:

To determine the prevalence, risk factors of MRSA infections in community and hospital.

Settings:

The incidence and risk factors for CA-MRSA and HA-MRSA among patients of medical, surgical, and pediatrics wards and ICU at a Kuwaiti teaching hospital between 1 March 2011 and 30 November 2011 were studied.

Materials and Methods:

Cultures for MRSA were taken from nasal (nostril), groin, axilla, wound, sputum, or throat, and the inguinal area in all enrolled patients upon admission. All preserved isolates were examined for their susceptibility to different types of antibiotics.

Results and Conclusion:

A total of 71 MRSA patients admitted to different hospital wards were examined. Among these patients, 52 (73.2%) were carriers of MRSA before they were admitted to the hospital. Nineteen patients (26.8%) were found to have acquired MRSA during their stay in the hospital. Twenty-nine patients (40.8%) were given mupirocin local skin antibiotic. Binomial and the t-test (paired) were used to compare the prevalence of CA-MRSA and HA-MRSA; significant correlation (P < 0.05) between the type of MRSA and different wards, sites, and lengths of hospital stay was found. The level of serum albumin that is routinely measured at hospital admission is a predictor to MRSA infection. This study suggests that S. aureus and MRSA should become a national priority for disease control to avoid outbreaks.

Community-associated methicillin-resistant Staphylococcus aureus colonization burden in HIV-infected patients

BACKGROUND

The epidemic of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has had a disproportionate impact on patients with human immunodeficiency virus (HIV).

METHODS

We evaluated CA-MRSA colonization burden (number of colonized sites per total number sampled) among HIV-infected and HIV-negative inpatients within 72 hours of hospitalization. From March 2011 through April 2012, we obtained cultures from nasal and extranasal sites (throat, axilla, inguinal, perirectal, and chronic wound if present) and collected risk factor data.

RESULTS

Of 745 patients (374 HIV-infected, 371 HIV-negative), 15.7% were colonized with CA-MRSA at any site: 20% of HIV and 11% of HIV-negative patients (relative prevalence=1.8, P=.002). HIV-infected patients had a higher prevalence of nasal, extranasal, and exclusive extranasal colonization as well as higher colonization burden. Perirectal and inguinal areas were the extranasal sites most frequently colonized, and 38.5% of colonized patients had exclusive extranasal colonization. Seventy-three percent of isolates were identified as USA300. Among HIV-infected patients, male sex, younger age, and recent incarceration were positively associated whereas Hispanic ethnicity was negatively associated with higher colonization burden. Among HIV-negative patients, temporary housing (homeless, shelter, or substance abuse center) was the only factor associated with higher colonization burden. Predictors of USA300 included HIV, younger age, illicit drug use, and male sex; all but 1 colonized individual with current or recent incarceration carried USA300.

CONCLUSIONS

HIV-infected patients were more likely to have a higher CA-MRSA colonization burden and carry USA300. In certain populations, enhanced community and outpatient-based infection control strategies may be needed to prevent CA-MRSA cross-transmission and infection.

Staphylococcus aureus colonization in children with community-associated Staphylococcus aureus skin infections and their household contacts

OBJECTIVES

To measure prevalence of Staphylococcus aureus colonization in household contacts of children with acute S aureus skin and soft tissue infections (SSTI), determine risk factors for S aureus colonization in household contacts, and assess anatomic sites of S aureus colonization in patients and household contacts.

DESIGN

Cross-sectional study.

SETTING

St Louis Children's Hospital Emergency Department and ambulatory wound center and 9 community pediatric practices affiliated with a practice-based research network.

PARTICIPANTS

Patients with community-associated S aureus SSTI and S aureus colonization (in the nose, axilla, and/or inguinal folds) and their household contacts.

OUTCOME MEASURES

Colonization of household contacts of pediatric patients with S aureus colonization and SSTI.

RESULTS

Of 183 index patients, 112 (61%) were colonized with methicillin-resistant S aureus (MRSA); 54 (30%), with methicillin-sensitive S aureus (MSSA); and 17 (9%), with both MRSA and MSSA. Of 609 household contacts, 323 (53%) were colonized with S aureus: 115 (19%) with MRSA, 195 (32%) with MSSA, and 13 (2%) with both. Parents were more likely than other household contacts to be colonized with MRSA (odds ratio, 1.72; 95% CI, 1.12 to 2.63). Methicillin-resistant S aureus colonized the inguinal folds more frequently than MSSA (odds ratio, 1.67; 95% CI, 1.16 to 2.41), and MSSA colonized the nose more frequently than MRSA (odds ratio, 1.75; 95% CI, 1.19 to 2.56).

CONCLUSIONS

Household contacts of children with S aureus SSTI had a high rate of MRSA colonization compared with the general population. The inguinal fold is a prominent site of MRSA colonization, which may be an important consideration for active surveillance programs in hospitals.

Epidemiologic Similarities in Pediatric Community-Associated Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus in the San Francisco Bay Area

BACKGROUND

Risk factors differentiating methicillin-resistant Staphylococcus aureus (MRSA) from methicillin-sensitive S aureus (MSSA) infections in the pediatric community have been unclear.

METHODS

We performed a prospective case-comparison investigation of clinical, epidemiological, and molecular factors in pediatric community-associated (CA) MRSA and MSSA cases in the San Francisco Bay Area. Chart reviews were conducted in 270 CA-MRSA and 313 CA-MSSA cases. Fifty-eight CA-MRSA (21.4%) and 95 CA-MSSA (30.4%) cases were interviewed. Molecular typing was performed on 111 isolates.

RESULTS

MSSA represented 53.7% of CA cases and was more likely to cause invasive disease (6.2% vs 1.1%, P = .004). Few potential epidemiologic risk factors distinguished CA-MRSA from CA-MSSA. No differences were found in factors related to crowding, cleanliness, or prior antibiotic use. Compromised skin integrity due to eczema (24.3% vs 13.5%, P = .001) was associated with CA-MSSA. Many exposures to potentially infected or colonized contacts or contaminated objects were assessed; only three were associated with CA-MSSA: having a household contact who had surgery in the past year (18.9% vs 6.0%, P = .02), and regular visits to a public shower (9.1% vs 2.0%, P = .01) or gym (12.6% vs 3.3%, P = .04). Molecular typing identified clonal complex 8 as the predominant genetic lineage among CA-MRSA (96.4%) and CA-MSSA (39.3%) isolates.

CONCLUSIONS

In the context of recent heightened focus on CA-MRSA, the burden of serious disease caused by CA-MSSA among children should not be overlooked. MRSA and MSSA may be growing epidemiologically similar; thus, research, clinical, and public health efforts should focus on S aureus as a single entity.

Self-reported incidence of skin and soft tissue infections among deployed US military

The incidence of skin and soft tissue infections has steadily increased over the past decade, and military populations, particularly recruits, have been affected. However, the epidemiology of skin and soft tissue infections in deployed personnel has not previously been described. We conducted a cross-sectional study of United States military personnel in mid-deployment using self-reported questionnaire data containing 11 demographic questions and 20 questions related to skin and soft tissue infections. The primary outcome was self-reported incident SSTI. Descriptive analyses were conducted and incidence estimates calculated. Multivariable regression models were developed to evaluate the association between SSTI and important covariates. Self-reported treatment modalities and effect on work performance were also assessed. The study was approved by the Institutional Review Board. 2125 questionnaires were completed over 12 months using convenience sampling. 110 personnel (5%) reported one or more skin and soft tissue infection during their most recent employment, for an incidence of 52 cases per 100,000 person-days. The majority reported a single infection. A higher proportion of individuals reporting skin and soft tissue infection were female, reported antibiotic use in the 6 months prior to completing the survey, had a family member in the healthcare occupation, and were senior enlisted or officers. 40 (36%) were treated with antibiotics and 24 (22%) underwent incision and drainage. Less than 5% (3 patients) required admission. Eighty eight respondents (81%), reported no days of lost job performance. There is a higher than expected incidence of skin and soft tissue infections in deployed military personnel. Although fewer than 20% of patients report missing at least one day of work, this can have a significant impact on the military mission. Further study should be conducted into how to prevent skin and soft tissue infections in military populations.

Nasal carriage of methicillin resistant Staphylococcus aureus and their antibiotic susceptibility patterns in children attending day-care centers

Nasal colonization with community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) is being increasingly reported, especially in places where people are in close contact and in reduced hygiene, such as day-care centers. In this study we investigated the frequency of MRSA colonization and their antibiotic susceptibility patterns in 1-6 years old children of day-care centers in Hamadan, West of Iran.Five hundred nasal swabs were collected from children of 27 day-care centers that had no risk factors for colonization by S. aureus. The specimens were cultured for isolation of S. aureus by standard methods. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. For evaluation of the frequency of erythromycin induced clindamycin resistance, disk approximation test (D-test) was applied.Totally, 148 (29.6%) children were colonized by S. aureus. Out of 260 male, 94 (36.2%) and of 240 female, 54 (22.5%) cases were nasal carriers of S. aureus (P value = 0.001). Six (4.1%) of the 148 S. aureus isolated from children were MRSA strains. None of MRSA and methicillin susceptible S. aureus (MSSA) was resistant to vancomycin and clindamycin. Three of the 6 strains of MRSA and 7 (4.9%) of the 142 MSSA strains were resistant to erythromycin, and D-test was positive in all of them.We conclude that the rate of colonization by S. aureus is high in children attending day-care centers but colonization with MRSA is not common in our areas. Clindamycin or trimethoprim-sulfamethoxazol could be used in mild to moderataly severe diseases caused by CA-MRSA. However, if the CA-MRSA isolates are erythromycin resistant, D-test should be carried out for detection of inducible clindamycin resistance.

A nosocomial outbreak of community-associated methicillin-resistant Staphylococcus aureus among healthy newborns and postpartum mothers

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has increasingly been isolated from individuals with no predisposing risk factors; however, such strains have rarely been linked to outbreaks in the hospital setting. The present study describes the investigation of an outbreak of CA-MRSA that occurred in the maternal-newborn unit of a large community teaching hospital in Toronto, Ontario.

METHODS

Screening and clinical specimens collected from mothers and newborns delivered during the outbreak period, as well as from staff on the affected unit, were submitted for microbiological testing. Computerized delivery logs and nursing notes were reviewed, and a case control study was conducted.

RESULTS

Analysis by pulsed-field gel electrophoresis revealed 38 babies and seven mothers with MRSA colonization and/or infection by the same unique strain (Canadian MRSA-10-related) from September to December 2004. Isolates were characterized as having the staphylococcal chromosome cassette mec type IVa and were positive for the Panton-Valentine leukocidin gene. No one health care worker was associated with all cases; however, mothers and newborns exposed to one particular nurse (Nurse A) were almost 23 times (odds ratio 22.7, 95% CI 3.3 to 195.9) more likely to acquire MRSA than those with no such contact. MRSA was successfully isolated from Nurse A and from an environmental swab of a telephone recently used by Nurse A; both isolates matched the pulsed-field gel electrophoresis pattern of the outbreak strain.

CONCLUSION

The first nosocomial outbreak of CA-MRSA among healthy newborns and postpartum mothers in Canada is described. Effective control of sustained MRSA transmission within an institution may require prompt identification, treatment and monitoring of colonized and/or infected staff.

Investigation of classical epidemiological links between patients harbouring identical, non-predominant meticillin-resistant Staphylococcus aureus genotypes and lessons for epidemiological tracking

According to molecular epidemiology theory, two isolates belong to the same chain of transmission if they are similar according to a highly discriminatory molecular typing method. This has been demonstrated in outbreaks, but is rarely studied in endemic situations. Person-to-person transmission cannot be established when isolates of meticillin-resistant Staphylococcus aureus (MRSA) belong to endemically predominant genotypes. By contrast, isolates of infrequent genotypes might be more suitable for epidemiological tracking. The objective of the present study was to determine, in newly identified patients harbouring non-predominant MRSA genotypes, whether putative epidemiological links inferred from molecular typing could replace classical epidemiology in the context of a regional surveillance programme. MRSA genotypes were defined using double-locus sequence typing (DLST) combining clfB and spa genes. A total of 1,268 non-repetitive MRSA isolates recovered between 2005 and 2006 in Western Switzerland were typed: 897 isolates (71%) belonged to four predominant genotypes, 231 (18%) to 55 non-predominant genotypes, and 140 (11%) were unique. Obvious epidemiological links were found in only 106/231 (46%) patients carrying isolates with non-predominant genotypes suggesting that molecular surveillance identified twice as many clusters as those that may have been suspected with classical epidemiological links. However, not all of these molecular clusters represented person-to-person transmission. Thus, molecular typing cannot replace classical epidemiology but is complementary. A prospective surveillance of MRSA genotypes could help to target epidemiological tracking in order to recognise new risk factors in hospital and community settings, or emergence of new epidemic clones.

Future challenges and treatment of Staphylococcus aureus bacteremia with emphasis on MRSA

Staphylococcus aureus bacteremia (SAB) is an urgent medical problem due to its growing frequency and its poor associated outcome. As healthcare delivery increasingly involves invasive procedures and implantable devices, the number of patients at risk for SAB and its complications is likely to grow. Compounding this problem is the growing prevalence of methicillin-resistant S. aureus (MRSA) and the dwindling efficacy of vancomycin, long the treatment of choice for this pathogen. Despite the recent availability of several new antibiotics for S. aureus, new strategies for treatment and prevention are required for this serious, common cause of human infection.

Panton-Valentine leukocidin associated staphylococcal disease: a cross-sectional study at a London hospital, England

Recently, there has been international concern at the rapid emergence of highly pathogenic strains of Staphylococcus aureus associated with a toxin called Panton-Valentine leukocidin (PVL). In the UK, these strains are considered to be rare and mainly severe. We estimate the proportion of staphylococcal infections that are caused by strains containing the PVL genes, and describe risk factors for these infections. Three hundred and ninety consecutive S. aureus clinical isolates, submitted for routine diagnostic purposes were screened for PVL genes. Risk factors for infection were identified from the patient medical record. 9.7% (95% CI 7.0-13.1%) of clinical isolates and 20.8% of skin and soft tissue specimens contained the genes for PVL. Methicillin-resistant S. aureus with PVL was rare (0.8% of all isolates) but PVL with methicillin-sensitive S. aureus was common (9.0% of all specimens). PVL infection was more frequent in males (OR 3.0, 95% CI 1.3-7.0), and in young adults aged 20-39 years (OR 3.7, 95% CI 1.3-10.4). Over half of PVL positive S. aureus infections originated in patients based in the community. Community-onset PVL-associated disease is common in the UK and mainly causes skin and soft tissue infections that do not require admission to hospital. Consideration should be given to current infection control strategy, which advocates household contact screening and decolonization on the assumption that PVL-associated disease is rare.

Effective state-based surveillance for multidrug-resistant organisms related to health care-associated infections

In September 2008, the Council of State and Territorial Epidemiologists and the Centers for Disease Control and Prevention sponsored a meeting of public health and infection-control professionals to address the implementation of surveillance for multidrug-resistant organisms (MDROs)-particularly those related to health care-associated infections. The group discussed the role of health departments and defined goals for future surveillance activities. Participants identified the following main points: (1) surveillance should guide prevention and infection-control activities, (2) an MDRO surveillance system should be adaptable and not organism specific, (3) new systems should utilize and link existing systems, and (4) automated electronic laboratory reporting will be an important component of surveillance but will take time to develop. Current MDRO reporting mandates and surveillance methods vary across states and localities. Health departments that have not already done so should be proactive in determining what type of system, if any, will fit their needs.

Methicillin-resistant Staphylococcus aureus: a community health threat

Methicillin-resistant Staphylococcus aureus (MRSA), one of the most common causes of infections, has been traditionally recognized as a nosocomial pathogen. However, in recent years, its epidemiology has radically changed, being now observed even more frequently in the community, and accounting for > 50% of staphylococcal infections in the US outpatient setting. Community-acquired (CA)-MRSA strains typically cause infections among otherwise healthy individuals, with risk factors differing from those of nosocomial MRSA. The clinical manifestations may range from a furuncle to life-threatening infections, such as necrotizing fasciitis and pneumonia. The antibiotic treatment of these infections may also differ because CA-MRSA strains often retain susceptibility to antimicrobials other than glycopeptides and newer agents. Moreover, the production of toxins, such as the Panton-Valentine leukocidin (PVL), should influence the antibiotic choice because in these cases the use of a combination therapy with antimicrobial agents able to decrease toxin production is suggested. There are still many unanswered key questions regarding the epidemiology, prevention, and treatment of CA-MRSA infections. This article reviews current knowledge of CA-MRSA.

Factors associated with nasal colonization of methicillin-resistant Staphylococcus aureus among healthy children in Taiwan

Methicillin-resistant Staphylococcus aureus (MRSA) has been identified as a major cause of community-associated (CA) S. aureus infections in the past decade. The main reservoir in the community for MRSA and the factors contributing to its worldwide spread remain poorly defined. Between July 2005 and June 2008, a total of 6,057 healthy children 2 to 60 months of age were screened for carriage of S. aureus and Streptococcus pneumoniae in Taiwan. The prevalence and epidemiological factors influencing MRSA carriage were determined. MRSA strains were tested for antimicrobial susceptibility and underwent molecular characterization. The overall prevalences of MRSA and S. aureus carriage were 7.8% and 23.2%, respectively. A majority (88%) of MRSA isolates belonged to a common Asian-Pacific CA-MRSA lineage, multilocus sequence type 59, and were resistant to multiple non-beta-lactam antibiotics. The carriage rate of MRSA was higher among subjects 2 to 6 months old (P < 0.0001), residing in northern Taiwan (P = 0.0003), and enrolled later in the study (P < 0.0001). MRSA colonization was associated with the number of children in the family (adjusted odds ratio [aOR], 1.114; 95% confidence interval [CI], 1.002 to 1.240; P = 0.0463) and day care attendance (aOR, 1.530; 95% CI, 1.201 to 1.949; P = 0.0006). Breast feeding (P < 0.0001) and colonization with S. pneumoniae (P = 0.0170) were protective against MRSA colonization. We concluded that epidemic CA-MRSA strains increasingly colonized Taiwanese children between 2005 and 2008. The carriage rate varied significantly across different demographical features. Crowding was an independent environmental risk factor that might accelerate CA-MRSA transmission in the community.

[Multiresistant bacteria in ophthalmology]

Multidrug-resistant bacteria have emerged as an increasing threat in many areas of medicine. The most prominent multidrug-resistant pathogens are methicillin-resistant S. aureus (MRSA), vancomycin-resistant MRSA (VMRSA), vancomycin-resistant enterococci (VRE), and Enterobacteriaceae with extended-spectrum beta-lactamase (ESBL). In particular, MRSA and VRE cause infections seen in ophthalmology. The lids, lacrimal duct, and ocular surface are frequently involved.

Association of methicillin-resistant Staphylococcus aureus (MRSA) USA300 genotype with mortality in MRSA bacteremia

OBJECTIVES

To evaluate the association of USA300 genotype with outcomes in persons with MRSA bacteremia and examine the epidemiology of MRSA bacteremia over time.

METHODS

Population-based surveillance for MRSA bacteremia was performed in 8-county Atlanta from 2005 to 2008. Cases of MRSA bacteremia were classified as healthcare-associated hospital-onset (HAHO), healthcare-associated community-onset (HACO), or community-associated (CA) disease. A survival analysis was performed on a nested cohort of cases with isolates characterized by pulse field gel electrophoresis (PFGE).

RESULTS

4344 MRSA bacteremia cases were identified; 2579 (59.4%) HACO, 1144 (26.3%) HAHO; and 601 (13.8%) CA. Overall incidence rates of MRSA bacteremia declined from 33.9/100,000 in 2005-24.8/100,000 in 2008. Rates were highest in persons ≥ 65 years, blacks, males, and persons with AIDS. In multivariate analysis of 1104 cases, USA300 genotype was associated with increased in-hospital mortality (HR 1.63, 95% CI 1.19-2.23). USA300 strains were also associated with increased mortality when compared to USA100 strains (HR 1.79, 95% CI 1.24-2.58).

CONCLUSIONS

MRSA bacteremia incidence declined over 4 years but CA disease rates remained stable. Persons with HIV, the elderly, and blacks were disproportionately affected. Bacteremia due to USA300 MRSA strains was associated with increased mortality, suggesting that USA300 strains may be more virulent.

Methicillin-resistant Staphylococcus aureus colonization in HIV-infected outpatients is common and detection is enhanced by groin culture

SUMMARYAlthough high rates of clinical infection with methicillin-resistant Staphylococcus aureus (MRSA) have been reported in HIV-infected adults, data on MRSA colonization are limited. We enrolled HIV-infected adults receiving care at the Atlanta VA Medical Center. Swabs from each participant's nares and groin were cultured with broth enrichment for S. aureus. Of 600 HIV-infected adults, 79 (13%) were colonized with MRSA and 180 (30%) with methicillin-susceptible S. aureus. MRSA pulsed-field gel electrophoresis types USA300 (n=44, 54%) and USA500/Iberian (n=29, 35%) predominated. Inclusion of groin swabs increased MRSA detection by 24% and USA300 detection by 38%. In multivariate analysis, MRSA colonization compared to no MRSA colonization was associated with a history of MRSA clinical infection, rarely or never using condoms, and contact with prisons and jails. In summary, the prevalence of MRSA colonization was high in this study of HIV-infected adults and detection of USA300 was enhanced by groin culture.

Community-Associated Methicillin-Resistant Staphylococcus Aureus Skin and Soft Tissue Infections

The prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections is increasing globally and in Singapore. Skin and soft tissue infections (SSTIs) are the most common manifestations, ranging from common furuncles to the rare but life-threatening necrotizing fasciitis. Surgical drainage and debridement where feasible are the mainstay of therapy, whereas MRSA-active antibiotics are essential when surgery is not possible or as adjunctive therapy for severe and/or complicated SSTIs. In itself, the continued inexorable rise in CA-MRSA rates poses difficult challenges for primary healthcare and hospital infection control. Innovative approaches are required to mitigate its impact in both the community and hospital settings.

Staphylococcus aureus: a continuously evolving and formidable pathogen in the neonatal intensive care unit

Staphylococcus aureus is a continuously evolving and formidable pathogen that has been a problem for both healthy and sick neonates for decades. Much focus over the past 20 years has been on hospital-associated methicillin-resistant S aureus (HA-MRSA); however, a global epidemic because of virulent community-associated MRSA (CA-MRSA) that has no "fitness cost" for carrying antibiotic-resistance genes has moved into neonatal intensive care units (NICUs). Recently, methicillin-susceptible S aureus has adopted some of the virulence factors of CA-MRSA and is an increasingly common cause of hospital-acquired infections in NICUs. This article reviews the changing epidemiology, clinical manifestations, and treatment of S aureus in neonates.

Nanosized aluminum altered immune function

On the basis of their uses in jet fuels and munitions, the most likely scenario for aluminum nanoparticle (NP) exposure is inhalation. NPs have been shown to be capable of penetrating deep into the alveolar regions of the lung, and therefore human alveolar macrophages (U937) with human type II pneumocytes (A549) were cultured together and exposed to NPs dispersed in an artificial lung surfactant to more accurately mimic the lung microenvironment. Two types of NPs were evaluated: aluminum (Al) and aluminum oxide (Al2O3). Following a 24-h incubation, cell viability was assessed using MTS, and mild toxicity was observed at higher doses with the U937 cells affected more than the A549. Since the U937 cells provided protection from NP toxicity, the cocultures were exposed to a benign concentration of NPs and infected with the respiratory pathogen community-associated methicillin-resistant Staphylococcus aureus (ca-MRSA) to determine any changes in cellular function. Phagocytosis assays demonstrated that the NPs impaired phagocytic function, and bacterial growth curves confirmed that this reduction in phagocytosis was not related to NP-bacteria interactions. Furthermore, NFkappaB PCR arrays and an IL-6 and TNF-alpha real time PCR demonstrated that both types of NPs altered immune response activation. This change was confirmed by ELISA assays that evaluated the secretion of IL-6, IL-8, IL-10, IL-1beta, and TNF-alpha and illustrated that the NPs repressed secretion of these cytokines. Therefore, although the NPs were not toxic to the cells, they did impair the cell's natural ability to respond to a respiratory pathogen regardless of NP composition.

Public health surveillance for methicillin-resistant Staphylococcus aureus: comparison of methods for classifying health care- and community-associated infections

OBJECTIVES

We compared 3 methods for classifying methicillin-resistant Staphylococcus aureus (MRSA) infections as health care associated or community associated for use in public health surveillance.

METHODS

We analyzed data on MRSA infections reported to the Michigan Department of Community Health from October 1, 2004, to December 31, 2005. Patient demographics, risk factors, infection information, and susceptibility were collected for 2151 cases. We classified each case by the health care risk factor, infection-type, and susceptibility pattern methods and compared the results of the 3 methods.

RESULTS

Demographic, clinical, and microbiological variables yielded similar health care-associated and community-associated distributions when classified by risk factor and infection type. When 2 methods yielded the same classifications, the overall distribution was similar to classification by 3 methods. No specific combination of 2 methods was superior.

CONCLUSIONS

MRSA categorization by 2 methods is more accurate than it is by a single method. The health care risk factor and infection-type methods yield comparable classification results. Accuracy is increased by using more variables; however, further research is needed to identify the optimal combination.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infections

PURPOSE OF REVIEW

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has become increasingly important as a cause of skin and soft tissue infections (SSTIs), particularly abscesses, in patients seen in the emergency department setting. The antibiotic sensitivity profile of Staphylococcus aureus isolates from SSTIs has changed over time in many geographic locations. Whether antibiotics are needed in the management of skin abscesses, and, if so, when, is controversial.

RECENT FINDINGS

A number of studies have looked at antibiotic therapy in conjunction with incision and drainage in managing abscesses. Factors evaluated were resolution of infection, need for change in antibiotic therapy, hospitalization after initial outpatient management, need for an additional drainage procedure, and recurrence of infection within 30 days after the initial incision and drainage procedure. For abscesses, clinical failure was associated with lack of adequate incision and drainage and not antibiotic use, regardless of the size of the abscess or the choice of antibiotic therapy. For other soft tissue infections, when antibiotic susceptibility data were available for the infection (impetigo or cellulitis with purulent drainage but no abscess), there was no difference in clinical resolution of MRSA infection even if the infecting organism was resistant to the antibiotic chosen for therapy.

SUMMARY

CA-MRSA has become an important cause of SSTIs. Current data suggest that most abscesses can be treated successfully with incision and drainage alone. Antibiotic choice is more crucial for management of cellulitis and should be guided by the prevalence of CA-MRSA in the community and its antibiotic susceptibility profile.

The human nasal microbiota and Staphylococcus aureus carriage

Background

Colonization of humans with Staphylococcus aureus is a critical prerequisite of subsequent clinical infection of the skin, blood, lung, heart and other deep tissues. S. aureus persistently or intermittently colonizes the nares of ∼50% of healthy adults, whereas ∼50% of the general population is rarely or never colonized by this pathogen. Because microbial consortia within the nasal cavity may be an important determinant of S. aureus colonization we determined the composition and dynamics of the nasal microbiota and correlated specific microorganisms with S. aureus colonization.

Methodology/Principal Findings

Nasal specimens were collected longitudinally from five healthy adults and a cross-section of hospitalized patients (26 S. aureus carriers and 16 non-carriers). Culture-independent analysis of 16S rRNA sequences revealed that the nasal microbiota of healthy subjects consists primarily of members of the phylum Actinobacteria (e.g., Propionibacterium spp. and Corynebacterium spp.), with proportionally less representation of other phyla, including Firmicutes (e.g., Staphylococcus spp.) and Proteobacteria (e.g. Enterobacter spp). In contrast, inpatient nasal microbiotas were enriched in S. aureus or Staphylococcus epidermidis and diminished in several actinobacterial groups, most notably Propionibacterium acnes. Moreover, within the inpatient population S. aureus colonization was negatively correlated with the abundances of several microbial groups, including S. epidermidis (p = 0.004).

Conclusions/Significance

The nares environment is colonized by a temporally stable microbiota that is distinct from other regions of the integument. Negative association between S. aureus, S. epidermidis, and other groups suggests microbial competition during colonization of the nares, a finding that could be exploited to limit S. aureus colonization.

Community-based intervention to manage an outbreak of MRSA skin infections in a county jail

This article describes a community-based intervention to manage an outbreak of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infections in a midwestern county jail. A systematic investigation conducted by a family medicine residency program identified 64 total cases and 19 MRSA cases between January 1 and December 31, 2007. Factors contributing to MRSA transmission included inadequate surveillance, lack of antibacterial soap, and a defective laundry process. All 19 isolates were CA-MRSA and all seven tested by pulsed-field gel electrophoresis (PFGE) were USA300. Four of the seven isolates showed variation of their PFGE patterns. A primary care approach using community-based resources effectively reduced the number of cases in this heterogeneous outbreak of CA-MRSA, with the last MRSA being isolated in October 2007.

Patient referral patterns and the spread of hospital-acquired infections through national health care networks

Rates of hospital-acquired infections, such as methicillin-resistant Staphylococcus aureus (MRSA), are increasingly used as quality indicators for hospital hygiene. Alternatively, these rates may vary between hospitals, because hospitals differ in admission and referral of potentially colonized patients. We assessed if different referral patterns between hospitals in health care networks can influence rates of hospital-acquired infections like MRSA. We used the Dutch medical registration of 2004 to measure the connectedness between hospitals. This allowed us to reconstruct the network of hospitals in the Netherlands. We used mathematical models to assess the effect of different patient referral patterns on the potential spread of hospital-acquired infections between hospitals, and between categories of hospitals (University medical centers, top clinical hospitals and general hospitals). University hospitals have a higher number of shared patients than teaching or general hospitals, and are therefore more likely to be among the first to receive colonized patients. Moreover, as the network is directional towards university hospitals, they have a higher prevalence, even when infection control measures are equally effective in all hospitals. Patient referral patterns have a profound effect on the spread of health care-associated infections like hospital-acquired MRSA. The MRSA prevalence therefore differs between hospitals with the position of each hospital within the health care network. Any comparison of MRSA rates between hospitals, as a benchmark for hospital hygiene, should therefore take the position of a hospital within the network into account.

The prevalence of hospital acquired infections is widely believed to reflect the quality of health care in individual hospitals, and is therefore often used as a benchmark. Intuitively, the idea is that infections spread more easily in hospitals with a poor quality of health care. This assumes that the rate at which admitted patients introduce new infections is the same for all hospitals. In this article, we show that this assumption is unlikely to be correct. Using national data on patient admissions, we are able to reconstruct the entire hospital network consisting of patients referred between hospitals. This network reveals that university hospitals admit more patients that recently stayed in other hospitals. Consequently, they are more likely to admit patients that still carry pathogens acquired during their previous hospital stay. Therefore, the prevalence of infections does not only reflect the quality of health care but also the connectedness to hospitals from which patients are referred. This phenomenon is missed at the single hospital level; our study is the first to address the connectedness between hospitals in explaining the prevalence of hospital acquired infections. Our findings imply that interventions should focus on hospitals that are central in the network of patient referrals.