Surgical site infections

Surgical site infections are a major contributor to morbidity and mortality in postsurgical care. Risk for surgical site infection is multifactorial and includes a host of microbial, patient-related, and procedure-related factors. Prevention of surgical infection relies on optimization of patient factors and use of a variety of evidence-based pharmacologic and nonpharmacologic measures. At the forefront of these measures is antimicrobial prophylaxis, which has been shown to be effective at reducing risk of surgical site infection. As guidelines for prevention of surgical site infection become increasingly complex and nuanced, surgical infection outcomes are increasing tied to quality outcome and performances measures.

Methicillin-sensitive and methicillin-resistant Staphylococcus aureus nasal carriage in a random sample of non-hospitalized adult population in northern Germany

Objective

The findings from truly randomized community-based studies on Staphylococcus aureus nasal colonization are scarce. Therefore we have examined point prevalence and risk factors of S. aureus nasal carriage in a non-hospitalized population of Braunschweig, northern Germany.

Methods

A total of 2026 potential participants were randomly selected through the resident's registration office and invited by mail. They were requested to collect a nasal swab at home and return it by mail. S. aureus was identified by culture and PCR. Logistic regression was used to determine risk factors of S. aureus carriage.

Results

Among the invitees, 405 individuals agreed to participate and 389 provided complete data which was included in the analysis. The median age of the participants was 49 years (IQR: 39–61) and 61% were females. S. aureus was isolated in 85 (21.9%; 95% CI: 18.0–26.2%) of the samples, five of which were MRSA (1.29%; 95% CI: 0.55–2.98%). In multiple logistic regression, male sex (OR = 3.50; 95% CI: 2.01–6.11) and presence of allergies (OR = 2.43; 95% CI: 1.39–4.24) were found to be associated with S. aureus nasal carriage. Fifty five different spa types were found, that clustered into nine distinct groups. MRSA belonged to the hospital-associated spa types t032 and t025 (corresponds to MLST CC 22), whereas MSSA spa types varied and mostly belonged to spa-CC 012 (corresponds to MLST CC 30), and spa-CC 084 (corresponds to MLST CC 15).

Conclusion

This first point prevalence study of S. aureus in a non-hospitalized population of Germany revealed prevalence, consistent with other European countries and supports previous findings on male sex and allergies as risk factors of S. aureus carriage. The detection of hospital-associated MRSA spa types in the community indicates possible spread of these strains from hospitals into the community.

Student self-screening for methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization in hand hygiene education

OBJECTIVE

To determine the feasibility and effectiveness of adding a hand hygiene exercise in self-screening for Methicillin-Resistant Staphylococcus Aureus (MRSA) nasal colonization to a health care delivery course for first-year pharmacy (P1) students.

DESIGN

About one month after students were trained in hand hygiene technique and indications, faculty members demonstrated how to self-screen for MRSA nasal colonization. Students were then asked to screen themselves during the required class time. Aggregated class results were shared and compared to prevalence estimates for the general population and health care providers.

ASSESSMENT

The 71 students present in class on the day of the self-screening exercise chose to participate. A survey comparing presecreening and postscreening responses indicated incremental improvements in student knowledge and awareness of health care associated infections and motivation to perform hand hygiene. On the written exam, student performance demonstrated improved knowledge compared to previous class years.

CONCLUSION

Self-screening for MRSA nasal colonization in a health care delivery course for P1 students increased students' motivation to perform hand hygiene techniques and follow indications promulgated by the World Health Organization.

The prevalence of methicillin-resistant Staphylococcus aureus colonization in emergency department fast track patients

BACKGROUND

Over the past two decades, methicillin-resistant Staphylococcus aureus (MRSA) has evolved from a hospital-associated infection to a significant public health threat in the community, causing outbreaks of soft tissue infections in otherwise healthy individuals. The goal of this study was to determine the prevalence of nasal MRSA colonization in low acuity Emergency Department (ED) Fast Track patients in order to better characterize the epidemiology of this pathogen.

METHODS

We conducted a cross-sectional study of a convenience sample of adult patients from our ED Fast Track. Nasal swabs were analyzed for MRSA using a polymerase chain reaction assay. Study participants completed a survey assessing traditional risk factors for CA-MRSA colonization.

RESULTS

A total of 106 ED Fast Track patients were tested. Four (3.8%, 95% CI 1.5%-9.3%) were MRSA positive. Three traditional CA-MRSA risk factors (personal history of abscess, family history of abscess, and participation in contact sports) were examined. In patients with a positive MRSA nasal swab, only a personal prior history of abscess retained signifi cance (OR 33, 95% CI 1.7-676, P=0.02).

CONCLUSION

This study found a higher prevalence of nasal MRSA colonization in low acuity ED Fast Track patients compared with historical community surveillance studies. A personal history of prior abscess was a signifi cant risk for CA-MRSA carriage.

Methicillin-resistant Staphylococcus aureus biofilm formation on dacryocystorhinostomy silicone tubes depends on the genetic lineage

PURPOSE

The aim of this study was to investigate biofilm formation on silicone tubes by genetically diverse methicillin-resistant Staphylococcus aureus (MRSA) strains.

METHODS

Capacity of biofilm formation on dacryocystorhinostomy silicone tubes was tested on 30 MRSA strains. Identification and methicillin resistance were confirmed by PCR for nuc and mecA genes. Strains were genotypically characterised (SCCmec, agr and spa typing). Biofilm formation was tested in microtiter plate and on silicone tubes.

RESULTS

Tested MRSA strains were classified into SCCmec type I (33.3%), II (3.3%), III (20.0%), IV (26.7%) and V (16.7%), agr type I (56.7%), II (36.7%) and III (6.6%), and eight spa clonal complexes (CCs). All tested MRSA strains showed ability to form biofilm on microtiter plate. Capacity of biofilm formation on silicone tubes was as follows: 33.3% of strains belonged to the category of low biofilm producers, and 66.7% to moderate biofilm producers. There was statistically significant correlation between spa CC and the category of biofilm production on silicone tubes (p = 0.01): CC5 and CC45 with moderate amount of biofilm, and CC8 with low amount of biofilm. A moderate amount of biofilm formed on silicone tubes correlated with agr type II MRSA strains (p = 0.008).

CONCLUSIONS

Biofilm formation by MRSA on silicone tubes is highly dependent on genetic characteristics of the strains. Therefore, MRSA genotyping may aid the determination of the possibility of biofilm-related ocular device infections. Genotyping and biofilm quantification may be helpful in determining when decolonisation and cohort isolation are required to prevent device-related infections.

Staphylococcus aureus nasopharyngeal carriage in rural and urban northern Vietnam

Background

Staphylococcus aureus is a common human pathogen that can colonise the respiratory tract and cause infection. Here we investigate the risk factors associated with nasopharyngeal carriage of S. aureus (including methicillin-resistant S. aureus [MRSA]) in Vietnam.

Methods

Between February and June 2012, nasal and pharyngeal swabs for S. aureus culture, and demographic and socioeconomic data were taken from 1016 participants in urban and rural northern Vietnam, who were randomly selected from pre-specified age strata.

Results

Overall S. aureus prevalence was 303/1016 (29.8%; adjusted for age: 33.8%). Carriage in the main cohort was found to be associated with younger age (≤5 years [OR 3.13, CI 1.62–6.03]; 6–12 [OR 6.87, CI 3.95–11.94]; 13–19 [OR 6.47, CI 3.56–11.74]; 20–29 [OR 4.73, CI 2.40–9.31]; 30–59 [OR 1.74, CI 1.04–2.92); with ≥60 as reference), living in an urban area (OR 1.36, CI 1.01–1.83) and antibiotics use (OR 0.69, CI 0.49–0.96). MRSA was detected in 80/1016 (7.9%). Being aged ≤5 years (OR 4.84, CI 1.47–15.97); 6–12 (OR 10.21, CI 3.54–29.50); 20–29 (OR 4.01, CI 1.09–14.77) and wealth (>3/5 wealth index, OR 1.63 CI 1.01–2.62) were significant risk factors for MRSA carriage.

Conclusions

Nasopharyngeal carriage of S. aureus is present in one-third of the Vietnamese population, and is more prevalent among children. Pharyngeal carriage is more common than nasal carriage. Risk factors for S. aureus (including MRSA) carriage are identified in the community.

Quantitative assessment of human MRSA risks from swine

The public health community, news media, and members of the general public have expressed significant concern that methicillin-resistant Staphylococcus aureus (MRSA) transmitted from pigs to humans may harm human health. Studies of the prevalence and dynamics of swine-associated (ST398) MRSA have sampled MRSA at discrete points in the presumed causative chain leading from swine to human patients, including sampling bacteria from live pigs, retail meats, farm workers, and hospital patients. Nonzero prevalence is generally interpreted as indicating a potential human health hazard from MRSA infections, but quantitative assessments of resulting risks are not usually provided. This article integrates available data from several sources to construct a conservative (plausible upper bound) probability estimate for the actual human health harm (MRSA infections and fatalities) arising from ST398-MRSA from pigs. The model provides plausible upper bounds of approximately one excess human infection per year among all U.S. pig farm workers, and one human infection per 31 years among the remaining total population of the United States. These results assume the possibility of transmission events not yet observed, so additional data collection may reduce these estimates further.

Microbiology, resistance patterns, and risk factors of mortality in ventilator-associated bacterial pneumonia in a Northern Thai tertiary-care university based general surgical intensive care unit

Background

Ventilator-associated pneumonia (VAP) occurrence, causative pathogens, and resistance patterns in surgical intensive care units (SICU) are different between Western and developing Asian countries. In Thailand, resistant organisms have progressively increased in the last decade. However, the evidence describing causes of VAP and its outcomes, especially secondary to resistant pathogens, in Asian developing countries’ SICUs is very limited. Therefore, the objective of this study was to describe the incidence, pathogen characteristics, and risk factors that impact mortality and patient survival following VAP in a tertiary Northern Thai SICU.

Methods

Between 2008 and 2012, VAP occurred in a total of 150 patients in Chiang Mai University’s general SICUs (6.3±2.8 cases per 1,000 mechanical ventilator days). The following clinical data were collected from 46 patients who died and 104 patients who survived: microbiologic results, susceptible patterns, and survival status at hospital discharge. Antimicrobial susceptibility patterns were classified as susceptible, multidrug resistant (MDR), extensively drug resistant (XDR), and pan-drug resistant (PDR). The hazard ratio (HR) was calculated for risk factor analysis.

Results

Regarding the microbiology, gram negative organisms were the major pathogens (n=142, 94.7%). The first three most common organisms were Acinetobacter baumannii (38.7% of all organisms, mortality 41.4%), Klebsiella pneumoniae (17.3%, mortality 30.8%), and Pseudomonas aeruginosa (16.7%, mortality 16%) respectively. The most common gram positive organism was Staphylococcus aureus (4.0%, mortality 50%). The median day of VAP occurrence were significantly different between the three groups (P<0.01): susceptible (day 4), MDR (day 5), and XDR (day 6.5). Only half of all VAP cases were caused by susceptible organisms. Antibiotic resistance was demonstrated by 49.3% of the gram negative organisms and 62.5% of the gram positive organisms. Extensive drug resistance was evident only in Acinetobacter baumannii (30.6%) and Pseudomonas aeruginosa (1.3%). No pan-drug resistance was found during surveillance. The significant HR risk factors were age (P=0.03), resistant organisms (P=0.04), XDR (P=0.02), and acute physiology and chronic health evaluation II score (<0.01). Acinetobacter baumannii (P=0.06) and intubation due to severe sepsis (P=0.08) demonstrated a trend toward a significant increase in the HR. On the other hand, there were significantly decreased HRs in trauma patients (P=0.01). Initial administration of appropriate antibiotic therapy had a tendency toward a significant decrease in the HR (P=0.08).

Conclusion

Gram negative organisms were the primary cause of bacterial VAP in Chiang Mai University’s general SICU. Resistant strains were present in half of all VAP cases and were associated with the day of VAP onset. Regarding risk factors, age, acute physiology, chronic health evaluation II score, resistant organisms (especially XDR), and being a non-trauma patient increased the risk of mortality.

Temporal association of infant immunisation with pneumococcal conjugate vaccine on the ecology of Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus nasopharyngeal colonisation in a rural South African community

BACKGROUND

Immunisation of children with pneumococcal conjugate vaccines (PCV) may affect the bacterial-ecology of the nasopharynx, including colonisation by Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus. The aim of this study was to evaluate the effect of infant PCV-immunisation on the nasopharyngeal ecology of these potentially pathogenic bacteria in a rural African setting.

METHODS

Two cross sectional surveys were undertaken from May to October in 2009 (Period-1) which coincided with the introduction of 7-valent PCV (PCV7) and in May-October 2011 (Period-2). Consenting household members, where there was a child <2 years of age in residence, had nasopharyngeal swabs undertaken for culture.

RESULTS

From Period-1 to Period-2 in children 0-2 years and 3-12 years, prevalence of overall S. pneumoniae colonisation decreased from 74.9% to 67.0% (p<0.001) and H. influenzae declined among children 3-12 years (55.1-45.3%, p<0.001) but not among those <2 years. The prevalence of S. aureus remained unchanged in all children. Competitive associations were found between S. pneumoniae and S. aureus and between H. influenzae and S. aureus among children. In individuals >12 years, the prevalence of colonisation decreased from 11.2% to 6.8%, 16.7% to 8.8% and 31.2% to 23.7% for S. pneumoniae, H. influenzae and S. aureus, respectively; p<0.001 for all comparions. Synergistic relationships for S. aureus with H. influenzae and S. pneumoniae were observed in both periods among this group.

Mouse models for infectious diseases caused by Staphylococcus aureus

Staphylococcus aureus - a commensal of the human skin, nares and gastrointestinal tract - is also a leading cause of bacterial skin and soft tissue infection (SSTIs), bacteremia, sepsis, peritonitis, pneumonia and endocarditis. Antibiotic-resistant strains, designated MRSA (methicillin-resistant S. aureus), are common and represent a therapeutic challenge. Current research and development efforts seek to address the challenge of MRSA infections through vaccines and immune therapeutics. Mice have been used as experimental models for S. aureus SSTI, bacteremia, sepsis, peritonitis and endocarditis. This work led to the identification of key virulence factors, candidate vaccine antigens or immune-therapeutics that still require human clinical testing to establish efficacy. Past failures of human clinical trials raised skepticism whether the mouse is an appropriate model for S. aureus disease in humans. S. aureus causes chronic-persistent infections that, even with antibiotic or surgical intervention, reoccur in humans and in mice. Determinants of S. aureus evasion from human innate and adaptive immune responses have been identified, however only some of these are relevant in mice. Future research must integrate these insights and refine the experimental mouse models for specific S. aureus diseases to accurately predict the failure or success for candidate vaccines and immune-therapeutics.

Propionibacterium-produced coproporphyrin III induces Staphylococcus aureus aggregation and biofilm formation

The majority of bacteria detected in the nostril microbiota of most healthy adults belong to three genera: Propionibacterium, Corynebacterium, and Staphylococcus. Among these staphylococci is the medically important bacterium Staphylococcus aureus. Almost nothing is known about interspecies interactions among bacteria in the nostrils. We observed that crude extracts of cell-free conditioned medium from Propionibacterium spp. induce S. aureus aggregation in culture. Bioassay-guided fractionation implicated coproporphyrin III (CIII), the most abundant extracellular porphyrin produced by human-associated Propionibacterium spp., as a cause of S. aureus aggregation. This aggregation response depended on the CIII dose and occurred during early stationary-phase growth, and a low pH (~4 to 6) was necessary but was not sufficient for its induction. Additionally, CIII induced plasma-independent S. aureus biofilm development on an abiotic surface in multiple S. aureus strains. In strain UAMS-1, CIII stimulation of biofilm depended on sarA, a key biofilm regulator. This study is one of the first demonstrations of a small-molecule-mediated interaction among medically relevant members of the nostril microbiota and the first description of a role for CIII in bacterial interspecies interactions. Our results indicate that CIII may be an important mediator of S. aureus aggregation and/or biofilm formation in the nostril or other sites inhabited by Propionibacterium spp. and S. aureus. Importance: Very little is known about interspecies interactions among the bacteria that inhabit the adult nostril, including Staphylococcus aureus, a potential pathogen that colonizes about a quarter of adults. We demonstrated that coproporphyrin III (CIII), a diffusible small molecule excreted by nostril- and skin-associated Propionibacterium spp., induces S. aureus aggregation in a manner dependent on dose, growth phase, and pH. CIII also induces S. aureus to form a plasma-independent surface-attached biofilm. This report is the first description of a role for CIII in bacterial interspecies interactions at any human body site and a novel demonstration that nostril microbiota physiology is influenced by small-molecule-mediated interactions.

Human mitochondrial DNA and endogenous bacterial surrogates for risk assessment of graywater reuse

Previous graywater risk assessment studies have focused on fecal contamination, yet the low density of fecal indicators may not provide the most useful approach to assess pathogen removal during graywater treatment. In this study, we employed high throughput bacterial sequencing and qPCR to elucidate potential microbial surrogates in wastewater sourced from an industrial laundry. In addition, we explored human mitochondrial DNA (HmtDNA) as a new, potentially more reliable molecular marker, because it can be unambiguously sourced, has a high copy number per cell, and is persistent when released from cells with no self-replication in graywater. Pyrosequencing and qPCR revealed that laundry water microbiota was dominated by the skin-associated bacteria Staphylococcus, Corynebacterium, and Propionibacterium (6.5, 5.7, 5.4 log10 copies/100 mL, respectively). While HmtDNA was less abundant (2.8 log10 copies/100 mL), it showed a strong positive correlation with the opportunistic pathogen Staphylococcus aureus (r=0.54, P=3.2×10(-4)) and closely followed a first-order exponential decay model (R2=0.98), remaining detectable in stored laundry graywater for up to 6 days at 20 °C. Based on abundance and persistence, we propose HmtDNA and total Staphylococcus as future laundry graywater treatment surrogates to potentially assess a wide dynamic range of pathogen removal.

The role of international travel in the spread of methicillin-resistant Staphylococcus aureus

BACKGROUND

Increasing international travel has facilitated the transmission of various multidrug-resistant bacteria-including methicillin-resistant Staphylococcus aureus (MRSA)-across continents. Individuals may acquire MRSA from the community, healthcare facilities, or even from animal exposure. Skin contact with colonized individuals, fomites, or animals during an overseas trip may result in either asymptomatic colonization or subsequent clinically significant MRSA disease. MRSA strains that harbor the Panton-Valentine leucocidin toxin are particularly associated with community transmission and may potentially have enhanced virulence resulting in serious skin and soft tissue infections or even necrotizing pneumonia. More importantly, secondary transmission events upon return from traveling have been documented, leading to potentially detrimental outbreaks within the community or the healthcare setting. We sought to review the existing literature relating to the role of various aspects of travel in the spread of MRSA. Risk factors for acquiring MRSA during travel together with the need for targeted screening of high-risk individuals will also be explored.

METHODS

Data for this article were identified via PubMed searches using a combination of search terms: "methicillin resistance," "MRSA," "livestock-associated MRSA," "community-associated MRSA," "travel," and "outbreak." The relevant articles were extensively perused to determine secondary sources of data.

RESULTS AND CONCLUSIONS

Our review of the current literature suggests that international travel plays a significant role in the transmission of MRSA, potentially contributing to the replacement of existing endemic MRSA with fitter and more transmissible strains. Therefore, selective and targeted screening of travelers with risk factors for MRSA colonization may be beneficial. Healthcare professionals and patients should be considered for screening if they were to return from endemic areas, with the former group decolonized before returning to patient care work, in order to reduce the transmission of MRSA to vulnerable patient populations.

Alternative strategies for proof-of-principle studies of antibacterial agents

The proof that a new antibacterial agent is not only active in vitro but also effective in vivo under clinically relevant conditions is currently provided (i) by using appropriate nonclinical models of infection and pharmacokinetic-pharmacodynamic (PK-PD) analysis providing evidence of the likelihood of clinical efficacy and (ii) by examining the study drug in exploratory clinical trials, as well as dose and schedule finding during phase II of clinical development. This approach is both time-consuming and costly. Furthermore, PK-PD targets for any novel antibacterial agent cannot be derived from studies with experimental animals. Therefore, alternative strategies have to be identified to prove the principle that a novel antibacterial agent is active under clinically relevant conditions. This review summarizes evidence that the quantitative analysis of shifts in the viable counts of pathogens in infected patients or the evaluation of the PD effect of an investigational agent on indicator organisms of the human resident microflora or colonizers of healthy volunteers, if paralleled with PK monitoring of serum and the target site, provides an alternative to a classical proof-of-principle study in the course of a phase II study program.

Isotonic saline nasal irrigation is an effective adjunctive therapy to intranasal corticosteroid spray in allergic rhinitis

BACKGROUND

This study was designed to determine if the addition of large-volume, low-positive pressure nasal irrigations delivered with isotonic sodium chloride (hereinafter "saline") added to intranasal corticosteroid therapy improves quality of life and objective measures of nasal breathing in patients with allergic rhinitis when compared with intranasal corticosteroid alone.

METHODS

A prospective, unblinded, single-arm pilot study was performed of patients with allergic rhinitis already on intranasal corticosteroid pharmacotherapy. Patients added large-volume low-pressure saline irrigation twice daily for 8 weeks to their ongoing regiment of nasal corticosteroid. Mini-Rhinoconjunctivitis Quality of life Questionnaire (mRQLQ) assessment and nasal peak inspiratory flow (NPIF) were performed at baseline and at 4 and 8 weeks.

RESULTS

A total of 40 patients were enrolled. Twice-daily nasal irrigation with isotonic saline significantly (p < 0.001) reduced mRQLQ scores, from 36.7 ± 20.48 (baseline) to 14.9 ± 11.03 (4 weeks) to 10.10 ± 10.65 (8 weeks). No significant changes were seen in NPIF, pattern use of nasal steroid use, or adverse events.

CONCLUSION

Large-volume, low-positive pressure nasal irrigation with isotonic saline is an effective adjunctive therapy to improve quality of life in patients with allergic rhinitis already on intranasal corticosteroid therapy. This study was a part of the clinical trial NCT01030146 registered at clinicaltrials.gov.

Multiplex real-time PCR for detection of Staphylococcus aureus, mecA and Panton-Valentine Leukocidin (PVL) genes from selective enrichments from animals and retail meat

The aim of this study was to compare a real-time PCR assay, with a conventional culture/PCR method, to detect S. aureus, mecA and Panton-Valentine Leukocidin (PVL) genes in animals and retail meat, using a two-step selective enrichment protocol. A total of 234 samples were examined (77 animal nasal swabs, 112 retail raw meat, and 45 deli meat). The multiplex real-time PCR targeted the genes: nuc (identification of S. aureus), mecA (associated with methicillin resistance) and PVL (virulence factor), and the primary and secondary enrichment samples were assessed. The conventional culture/PCR method included the two-step selective enrichment, selective plating, biochemical testing, and multiplex PCR for confirmation. The conventional culture/PCR method recovered 95/234 positive S. aureus samples. Application of real-time PCR on samples following primary and secondary enrichment detected S. aureus in 111/234 and 120/234 samples respectively. For detection of S. aureus, the kappa statistic was 0.68–0.88 (from substantial to almost perfect agreement) and 0.29–0.77 (from fair to substantial agreement) for primary and secondary enrichments, using real-time PCR. For detection of mecA gene, the kappa statistic was 0–0.49 (from no agreement beyond that expected by chance to moderate agreement) for primary and secondary enrichment samples. Two pork samples were mecA gene positive by all methods. The real-time PCR assay detected the mecA gene in samples that were negative for S. aureus, but positive for Staphylococcus spp. The PVL gene was not detected in any sample by the conventional culture/PCR method or the real-time PCR assay. Among S. aureus isolated by conventional culture/PCR method, the sequence type ST398, and multi-drug resistant strains were found in animals and raw meat samples. The real-time PCR assay may be recommended as a rapid method for detection of S. aureus and the mecA gene, with further confirmation of methicillin-resistant S. aureus (MRSA) using the standard culture method.

Colonization and infection of the skin by S. aureus: immune system evasion and the response to cationic antimicrobial peptides

Staphylococcus aureus (S. aureus) is a widespread cutaneous pathogen responsible for the great majority of bacterial skin infections in humans. The incidence of skin infections by S. aureus reflects in part the competition between host cutaneous immune defenses and S. aureus virulence factors. As part of the innate immune system in the skin, cationic antimicrobial peptides (CAMPs) such as the β-defensins and cathelicidin contribute to host cutaneous defense, which prevents harmful microorganisms, like S. aureus, from crossing epithelial barriers. Conversely, S. aureus utilizes evasive mechanisms against host defenses to promote its colonization and infection of the skin. In this review, we focus on host-pathogen interactions during colonization and infection of the skin by S. aureus and methicillin-resistant Staphylococcus aureus (MRSA). We will discuss the peptides (defensins, cathelicidins, RNase7, dermcidin) and other mediators (toll-like receptor, IL-1 and IL-17) that comprise the host defense against S. aureus skin infection, as well as the various mechanisms by which S. aureus evades host defenses. It is anticipated that greater understanding of these mechanisms will enable development of more sustainable antimicrobial compounds and new therapeutic approaches to the treatment of S. aureus skin infection and colonization.

The use of surveillance and preventative measures for methicillin-resistant staphylococcus aureus infections in surgical patients

The Agency for Healthcare Research & Quality (AHRQ) found that Methicillin-resistant Staphylococcus aureus (MRSA) is associated with up to 375,000 infections and 23,000 deaths in the United States. It is a major cause of surgical site infections, with a higher mortality and longer duration of care than Methicillin-sensitive Staphylococcus aureus. A multifactorial bundled approach is needed to control this epidemic, with single interventions unlikely to have a significant impact on attenuating MRSA infection rates. Active surveillance has been studied in a wide range of surgical patients, including surgical intensive care and non-intensive care units; cardiac, vascular, orthopedic, obstetric, head and neck cancer and gastrostomy patients. There is sufficient evidence demonstrating a beneficial effect of surveillance and eradication prior to surgery to recommend its use on an expanded basis. Studies on MRSA surveillance in surgical patients that were published over the last 10 years were reviewed. In at least five of these studies, the MRSA colonization status of patients was reported to be a factor in preoperative antibiotic selection, with the modification of treatment regiments including the switching to vancomycin or teicoplanin in MRSA positive preoperative patients. Several authors also used decolonization protocols on all preoperative patients but used surveillance to determine the duration of the decolonization. Universal decolonization of all patients, regardless of MRSA status has been advocated as an alternative prevention protocol in which surveillance is not utilized. Concern exists regarding antimicrobial stewardship. The daily and universal use of intranasal antibiotics and/or antiseptic washes may encourage the promotion of bacterial resistance and provide a competitive advantage to other more lethal organisms. Decolonization protocols which indiscriminately neutralize all bacteria may not be the best approach. If a patient's microbiome is markedly challenged with antimicrobials, rebuilding it with replacement commensal bacteria may become a future therapy. Preoperative MRSA surveillance allows the selection of appropriate prophylactic antibiotics, the use of extended decolonization protocols in positive patients, and provides needed data for epidemiological studies.

Modeling the transmission of community-associated methicillin-resistant Staphylococcus aureus: a dynamic agent-based simulation

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has been a deadly pathogen in healthcare settings since the 1960s, but MRSA epidemiology changed since 1990 with new genetically distinct strain types circulating among previously healthy people outside healthcare settings. Community-associated (CA) MRSA strains primarily cause skin and soft tissue infections, but may also cause life-threatening invasive infections. First seen in Australia and the U.S., it is a growing problem around the world. The U.S. has had the most widespread CA-MRSA epidemic, with strain type USA300 causing the great majority of infections. Individuals with either asymptomatic colonization or infection may transmit CA-MRSA to others, largely by skin-to-skin contact. Control measures have focused on hospital transmission. Limited public health education has focused on care for skin infections.

METHODS

We developed a fine-grained agent-based model for Chicago to identify where to target interventions to reduce CA-MRSA transmission. An agent-based model allows us to represent heterogeneity in population behavior, locations and contact patterns that are highly relevant for CA-MRSA transmission and control. Drawing on nationally representative survey data, the model represents variation in sociodemographics, locations, behaviors, and physical contact patterns. Transmission probabilities are based on a comprehensive literature review.

RESULTS

Over multiple 10-year runs with one-hour ticks, our model generates temporal and geographic trends in CA-MRSA incidence similar to Chicago from 2001 to 2010. On average, a majority of transmission events occurred in households, and colonized rather than infected agents were the source of the great majority (over 95%) of transmission events. The key findings are that infected people are not the primary source of spread. Rather, the far greater number of colonized individuals must be targeted to reduce transmission.

CONCLUSIONS

Our findings suggest that current paradigms in MRSA control in the United States cannot be very effective in reducing the incidence of CA-MRSA infections. Furthermore, the control measures that have focused on hospitals are unlikely to have much population-wide impact on CA-MRSA rates. New strategies need to be developed, as the incidence of CA-MRSA is likely to continue to grow around the world.

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.

Insights into nasal carriage of Staphylococcus aureus in an urban and a rural community in Ghana

The epidemiology of Staphylococcus aureus in the community in Ghana was never investigated prior to this study. The aims of the study were: i) to assess prevalence of nasal S. aureus carriage in Ghanaian people living in an urban and a rural area, and ii) to identify phenotypic and genotypic traits of strains isolated from the two communities. Nasal swabs were collected from healthy individuals living in an urban community situated in the suburb of the capital city, Accra (n = 353) and in a rural community situated in the Dangme-West district (n = 234). The overall prevalence of nasal carriage was 21% with a significantly higher prevalence in the urban (28%) than in the rural community (11%) (p<0.0001). The levels of antimicrobial resistance were generally low (<5%) except for penicillin (91%) and tetracycline (25%). The only two (0.3%) MRSA carriers were individuals living in the urban area and had been exposed to hospitals within the last 12 months prior to sampling. Resistance to tetracycline (p = 0.0009) and presence of Panton-Valentine leukocidin (PVL) gene (p = 0.02) were significantly higher among isolates from the rural community compared to isolates from the urban community. Eleven MLST clonal complexes (CC) were detected based on spa typing of the 124 S. aureus isolates from the two communities: CC8 (n = 36), CC152 (n = 21), CC45 (n = 21), CC15 (n = 18), CC121 (n = 6), CC97 (n = 6), CC30 (n = 5), CC5 (n = 5), CC508 (n = 4), CC9 (n = 1), and CC707 (n = 1). CC8 and CC45 were less frequent in the rural area than in the urban area (p = 0.02). These results reveal remarkable differences regarding carriage prevalence, tetracycline resistance, PVL content and clonal distribution of S. aureus in the two study populations. Future research may be required to establish whether such differences in nasal S. aureus carriage are linked to socio-economic differences between urban and rural communities in this African country.

Occupational exposure to Staphylococcus aureus and Enterococcus spp. among spray irrigation workers using reclaimed water

As reclaimed water use expands, it is important to evaluate potential occupational health risks from exposure to this alternative water source. We compared odds of colonization with methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible S. aureus (MSSA), vancomycin-resistant enterococci (VRE), and vancomycin-susceptible enterococci (VSE) between spray irrigation workers using reclaimed water and office worker controls. Nasal and dermal swabs from 19 spray irrigation workers and 24 office worker controls were collected and analyzed for MRSA, MSSA, VRE, and VSE. Isolates were confirmed using standard biochemical tests and polymerase chain reaction assays. Antimicrobial susceptibility testing was performed by Sensititre^® microbroth dilution. Data were analyzed by two-sample proportion, chi-square, Fisher’s exact tests, and logistic regression. No MRSA or VRE were detected in any samples. MSSA was detected in 26% and 29% of spray irrigators and controls, respectively. VSE was detected in 11% and 0% of spray irrigation workers and controls, respectively. The adjusted odds of MSSA, multidrug-resistant MSSA, and either MSSA or VSE colonization were greater among spray irrigation workers, however results were not statistically significant. Future studies with larger sample sizes are needed to further evaluate this relationship.

Seasonal evaluation of bioaerosols from indoor air of residential apartments within the metropolitan area in South Korea

The aims of the present study were to determine the levels of bioaerosols including airborne culturable bacteria (total suspended bacteria, Gram-positive bacteria, Staphylococcus, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and Gram-negative bacteria), fungi, endotoxin, and viruses (influenza A, influenza B, respiratory syncytial virus types A/B, parainfluenza virus types 1/2/3, metapnemovirus, and adenovirus) and their seasonal variations in indoor air of residential apartments. Of the total suspended bacteria cultured in an indoor environment, Staphylococcus was dominant and occupied 49.0 to 61.3% of indoor air. Among Staphylococcus, S. aureus were detected in 100% of households' indoor air ranging from 4 to 140 CFU/m(3), and 66% of households were positive for MRSA ranging from 2 to 80 CFU/m(3). Staphylococcus and S. aureus concentrations correlated with indoor temperature (adjusted β: 0.4440 and 0.403, p < 0.0001). Among respiratory viruses, adenovirus was detected in 14 (14%) samples and influenza A virus was detected in 3 (3%) samples regarding the indoor air of apartments. Adenovirus concentrations were generally higher in winter (mean concentration was 2,106 copies/m(3)) than in spring (mean concentration was 173 copies/m(3)), with concentrations ranging between 12 and 560 copies/m(3). Also, a strong negative correlation between adenovirus concentrations and relative humidity in indoor air was observed (r = -0.808, p < 0.01). Furthermore, temperature also negatively correlated with adenovirus concentrations (r = -0.559, p < 0.05).

Screening and characterization of Staphylococcus aureus from ophthalmology clinic surfaces: a proposed surveillance tool

PURPOSE

To screen environmental surfaces of an outpatient ophthalmic clinic for methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA); to identify the most commonly contaminated surfaces and to phenotype and genotype all collected isolates.

DESIGN

A single institution, 1-year prospective environmental study.

METHODS

Commonly touched surfaces in examination rooms and common areas were targeted and sampled on a quarterly basis for 1 year. Samples were collected using electrostatic cloths and swabs. S. aureus was isolated using nonselective and selective media. Morphologic characteristics and standard biologic testing were used to confirm staphylococcal species. S. aureus isolates were phenotypically (Kirby-Bauer method) and genotypically characterized (mecA confirmation, SCCmec typing and pulsed-field gel electrophoresis). Dendrogram analysis was used to establish genetic relatedness between the isolates.

RESULTS

Of 112 total samples, 27 (24%) and 5 (4%) were MSSA- and MRSA-positive, respectively. Both community-associated (SCCmec IV, USA300) and hospital-associated (SCCmec II, USA100) MRSA isolates were found. No single surface remained consistently positive with the same isolate over time, and molecular analysis demonstrated high levels of diversity among isolates. Doorknobs, slit-lamp headrests and chinrests, and computer keyboards were commonly found to be contaminated.

CONCLUSIONS

The proposed surveillance protocol successfully allowed the detection of both MSSA and MRSA contaminating important high-touch surfaces in a representative ophthalmology clinic. Frequently contaminated surfaces must be targeted for routine cleaning and disinfection because there is a constant introduction of clones over time. Hence, other clinics may consider implementing and adapting surveillance tools, like the one described here, to help them control these important nosocomial pathogens.

Staphylococcus aureus and staphylococcal food-borne disease: an ongoing challenge in public health

Staphylococcal food-borne disease (SFD) is one of the most common food-borne diseases worldwide resulting from the contamination of food by preformed S. aureus enterotoxins. It is one of the most common causes of reported food-borne diseases in the United States. Although several Staphylococcal enterotoxins (SEs) have been identified, SEA, a highly heat-stable SE, is the most common cause of SFD worldwide. Outbreak investigations have found that improper food handling practices in the retail industry account for the majority of SFD outbreaks. However, several studies have documented prevalence of S. aureus in many food products including raw retail meat indicating that consumers are at potential risk of S. aureus colonization and subsequent infection. Presence of pathogens in food products imposes potential hazard for consumers and causes grave economic loss and loss in human productivity via food-borne disease. Symptoms of SFD include nausea, vomiting, and abdominal cramps with or without diarrhea. Preventive measures include safe food handling and processing practice, maintaining cold chain, adequate cleaning and disinfection of equipment, prevention of cross-contamination in home and kitchen, and prevention of contamination from farm to fork. This paper provides a brief overview of SFD, contributing factors, risk that it imposes to the consumers, current research gaps, and preventive measures.

Nasal carriage of Staphylococcus aureus in Botucatu, Brazil: a population-based survey

Recent increases in the incidence and severity of staphylococcal infections renewed interest in studies that assess the burden of asymptomatic carriage of Staphylococcus aureus in the community setting. We conducted a population-based survey in the city of Botucatu, Brazil (122,000 inhabitants), in order to identify the prevalence of nasal carriage of Staphylococcus aureus (including methicillin-resistant strains). Nasal swabs were obtained from 686 persons over one year of age. Resistance to methicillin was assessed through phenotypic methods, identification of the mecA gene and typing of the Staphylococcal Chromosome Cassette mec (SCCmec). Methicillin-resistant S. aureus (MRSA) isolates were characterized using Pulsed-Field Gel Electrophoresis (PFGE), Multilocus Sequence Typing (MLST) and spa typing. Polymerase chain reaction was applied to identify genes coding for Panton-Valentine Leukocidin (PVL) in isolates. The prevalence of overall S. aureus carriage was 32.7% (95%CI, 29.2%–36.2%). Carriers were significantly younger (mean age, 28.1 versus 36.3 for non-carriers; OR for age, 0.98; 95%CI, 0.97–0.99) and likely to report recent skin infection (OR, 1.85; 95%CI, 1.03–3.34). Carriage of methicillin-resistant S. aureus (MRSA) was found in 0.9% of study subjects (95%CI, 0.4%–1.8%). All MRSA isolates harbored SCCmec type IV, and belonged to spa types t002 or t021, but none among them harbored genes coding for PLV. In MLST, most isolates belonged to clones ST5 or ST1776. However, we found one subject who carried a novel clone, ST2594. Two out of six MRSA carriers had household contacts colonized with isolates similar to theirs. Our study pointed to dissemination of community-associated MRSA among the Brazilian population.

Molecular epidemiology of environmental MRSA at an equine teaching hospital: introduction, circulation and maintenance

The role that environmental contamination might play as a reservoir and a possible source of Methicillin-resistant Staphylococcus aureus (MRSA) for patients and personnel at equine veterinary hospitals remains undefined, as the environment has only been monitored during outbreaks or for short periods. Therefore, the objectives of this study were to determine the monthly presence, distribution, and characteristics of environmental MRSA at an equine hospital, and to establish patterns of contamination over time using molecular epidemiological analyses. For this purpose, a yearlong active MRSA surveillance was performed targeting the environment and incoming patients. Antimicrobial susceptibility testing, SCCmec typing, PFGE typing, and dendrographic analysis were used to characterize and analyze these isolates. Overall, 8.6% of the surfaces and 5.8% of the horses sampled were positive for MRSA. The most common contaminated surfaces were: computers, feed-water buckets, and surgery tables-mats. Ninety percent of the isolates carried SCCmec type IV, and 62.0% were classified as USA500. Molecular analysis showed that new pulsotypes were constantly introduced into the hospital throughout the year. However, maintenance of strains in the environment was also observed when unique clones were detected for 2 consecutive months on the same surfaces. Additionally, pulsotypes were circulating throughout several areas and different contact surfaces of the hospital. Based on these results, it is evident that MRSA is constantly introduced and frequently found in the equine hospital environment, and that some contact surfaces could act as “hot-spots”. These contaminated surfaces should be actively targeted for strict cleaning and disinfection as well as regular monitoring.

Genetic Polymorphism of agr Locus and Antibiotic Resistance of Staphylococcus aureus at two hospitals in Pakistan

OBJECTIVE

The accessory gene regulator (agr) locus in Staphylococcus aureus (S. aureus) is a global regulator of quorum sensing and controls the production of virulence factors. This study was carried out to investigate the agr specific groups both in methicillin resistant and sensitive Staphylococcus aureus (MRSA and MSSA) and their relation with antibiotic resistance.

METHODS

A total of 90 clinical S. aureus isolates were studied from two tertiary care hospitals. The isolates were identified by standard biochemical tests. Methicillin resistance was confirmed by oxacillin and cefoxitin resistance. Multiplex PCR was used to determine the agr groups.

RESULTS

MRSA prevalence was found to be 53.3%.The agr groups' distribution in MRSA was as follows: 22 (45.8%) belonged to group I, 14 (29.1%) belonged to group III and 2 (4.1%) belonged to group II. agrIV was not detected in MRSA. For 17 isolates, the agr group was not detected.agr III isolates showed higher antibiotic resistance than agrI isolates except in case of oxacillin and linezolid.

CONCLUSIONS

Strict infection control policy and antibiotic guidelines should be adopted to control the problem of MRSA. Higher prevalence of agr I and agr III shows that they are dominant agr groups of our area.

Role of antibodies in protection elicited by active vaccination with genetically inactivated alpha hemolysin in a mouse model of staphylococcus aureus skin and soft tissue infections

Due to the emergence of highly virulent community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections, S. aureus has become a major threat to public health. A majority of CA-MRSA skin and soft tissue infections in the United States are caused by S. aureus USA300 strains that are known to produce high levels of alpha hemolysin (Hla). Therefore, vaccines that contain inactivated forms of this toxin are currently being developed. In this study, we sought to determine the immune mechanisms of protection for this antigen using a vaccine composed of a genetically inactivated form of Hla (HlaH35L). Using a murine model of skin and soft tissue infections (SSTI), we found that BALB/c mice were protected by vaccination with HlaH35L; however, Jh mice, which are deficient in mature B lymphocytes and lack IgM and IgG in their serum, were not protected. Passive immunization with anti-HlaH35L antibodies conferred protection against bacterial colonization. Moreover, we found a positive correlation between the total antibody concentration induced by active vaccination and reduced bacterial levels. Animals that developed detectable neutralizing antibody titers after active vaccination were significantly protected from infection. These data demonstrate that antibodies to Hla represent the major mechanism of protection afforded by active vaccination with inactivated Hla in this murine model of SSTI, and in this disease model, antibody levels correlate with protection. These results provide important information for the future development and evaluation of S. aureus vaccines.

A bundled approach to reduce methicillin-resistant Staphylococcus aureus infections in a system of community hospitals

Methicillin-resistant Staphylococcus aureus (MRSA) infections pose a significant challenge to U.S. healthcare facilities, but there has been limited study of initiatives to reduce infection and increase patient safety in community hospitals. To address this need, a multifaceted program for MRSA infection prevention was developed for implementation in 159 acute care facilities. This program featured five distinct tools-active MRSA surveillance of high-risk patients, enhanced barrier precautions, compulsive hand hygiene, disinfection and cleaning, and executive champions and patient empowerment-and was implemented during 1Q-2Q 2007. Postintervention (3Q 2007-2Q 2008), 10.2% of patients with high-risk for infection or complications due to MRSA had nasal colonization. Volume of disposable gown and alcohol-based hand sanitizer use increased substantially following program implementation. Self-reported rates, based on NHSN definitions, of healthcare-associated central line-associated bloodstream infections and ventilator-associated pneumonia due to MRSA decreased 39% (p < .001) and 54% (p < .001), respectively. Infection rates continued to decrease during the follow-up period (1Q-4Q 2009). This sustained improvement demonstrates that reducing healthcare-associated MRSA infections in a large number of diverse facilities is possible and that a "bundled" approach that translates science into clinical and executive performance expectations may aid in overcoming traditional barriers to implementation.

Identification of point mutations in clinical Staphylococcus aureus strains that produce small-colony variants auxotrophic for menadione

Staphylococcus aureus small-colony variants (SCVs) are implicated in chronic and relapsing infections that are difficult to diagnose and treat. Despite many years of study, the underlying molecular mechanisms and virulence effect of the small-colony phenotype remain incompletely understood. We sequenced the genomes of five S. aureus SCV strains recovered from human patients and discovered previously unidentified nonsynonymous point mutations in three genes encoding proteins in the menadione biosynthesis pathway. Analysis of genetic revertants and complementation with wild-type alleles confirmed that these mutations caused the SCV phenotype and decreased virulence for mice.

Methicillin-resistant Staphylococcus aureus colonization among health care workers in a downtown emergency department in Toronto, Ontario

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) acquired in the community, otherwise known as community-acquired MRSA, has emerged rapidly in recent years. Colonization with MRSA has been associated with an increased risk of symptomatic and serious infections and, in some settings, health care workers (HCWs) exhibit a higher prevalence of MRSA colonization.

OBJECTIVE

To determine MRSA colonization in emergency department (ED) HCWs in the setting of a moderate prevalence of MRSA in skin and soft tissue infections.

METHODS

The present study was conducted at a downtown ED in Toronto, Ontario. ED HCWs completed a brief questionnaire and swabs were taken from one anterior nare, one axilla and any open wounds (if present). Swabs were processed using standard laboratory techniques.

RESULTS

None of the 89 staff (registered nurses [n=55], physicians [n=15], other [n=19]) were MRSA positive and 25 (28.1%) were colonized with methicillin-susceptible S aureus.

CONCLUSIONS

Contrary to common belief among HCWs and previous studies documenting MRSA colonization of HCWs, MRSA colonization of this particular Canadian ED HCW cohort was very low and similar to that of the local population.

New insights into the prevention of staphylococcal infections and toxic shock syndrome

Staphylococcus aureus is a major human pathogen capable of causing various diseases, from skin infections to life-threatening pneumonia and toxic shock syndrome. S. aureus exoproteins, including superantigens, contribute significantly to the pathogenesis of this organism. Antibiotics inhibit growth, but often provide no protection from S. aureus exoproteins. With the emergence of antibiotic-resistant S. aureus, new therapeutic options to treat or prevent S. aureus-associated diseases are critical. Most S. aureus infections begin on the skin or mucosal surfaces from direct inflammatory or cytotoxic effects of exotoxins. Therefore, antitoxin therapies that prevent toxin production and prevent their effects on host cells are being researched. Current treatments for staphylococcal diseases and recent developments in antitoxin therapeutic agents and vaccines are reviewed.

Vancomycin and nephrotoxicity: just another myth?

BACKGROUND

Vancomycin is considered the drug of choice for methicillin-resistant Staphylococcus aureus infection; however, it has also been linked with nephrotoxicity in the past, sometimes leading to its substitution with linezolid. We hypothesized that patients treated with vancomycin for gram-positive (GP) infections would have an increased incidence of rise in creatinine and need for hemodialysis (HD) compared with patients receiving linezolid.

METHODS

This was a retrospective cohort study of a prospectively maintained database of all surgical patients treated with either vancomycin or linezolid for GP infections in a single intensive care unit from 2001 to 2008 and managed under a cycling antibiotic protocol. Patients were followed up until hospital discharge. Categorical and continuous variables were evaluated. Multivariable logistic regression was performed.

RESULTS

A total of 545 patients were treated for 1,046 GP infections (571 with vancomycin, 475 with linezolid) over 7 years. Patient demographics were similar between groups; however, the vancomycin group was associated with a longer treatment course (16.2 [0.5] days vs. 14.3 [0.5] days; p = 0.022). Unadjusted outcomes were similar between groups. Multivariable analysis revealed that Acute Physiology and Chronic Health Evaluation II score predicted an increase in creatinine levels greater than 1.0 following antibiotic therapy (relative risk [RR], 3.01; 95% confidence interval [CI], 1.22-7.42) and subsequent need for HD (RR, 3.07; 95% CI, 1.23-7.62). In addition, initial creatinine level predicted an increase in creatinine levels greater than 1.0 following antibiotic therapy (RR, 4.36; 95% CI, 1.46-12.99) and subsequent need for HD (RR, 10.83; 95% CI, 3.19-36.77). Linezolid was found to be protective regarding rise in creatinine levels greater than 1.0 following antibiotic therapy; however, this was only experienced when vancomycin trough levels greater than 20 were encountered (RR, 5.4;95% CI, 1.19-24.51).

CONCLUSION

These data suggest that vancomycin is minimally nephrotoxic and has a similar nephrotoxic profile as compared with linezolid when appropriate dosing is used, even among critically ill patients with complex infections.

LEVEL OF EVIDENCE

Therapeutic/care management, level II.

New insight into transmembrane topology of Staphylococcus aureus histidine kinase AgrC

Staphylococcus aureus accessory gene regulator (agr) locus controls the expression of virulence factors through a classical two-component signal transduction system that consists of a receptor histidine protein kinase AgrC and a cytoplasmic response regulator AgrA. An autoinducing peptide (AIP) encoded by agr locus activates AgrC, which transduces extracellular signals into the cytoplasm. Despite extensive investigations to identify AgrC-AIP interaction sites, precise signal recognition mechanisms remain unknown. This study aims to clarify the membrane topology of AgrC by applying the green fluorescent protein (GFP) fusion technique and the substituted cysteine accessibility method (SCAM). However, our findings were inconsistent with profile obtained previously by alkaline phosphatase. We report the topology of AgrC shows seven transmembrane segments, a periplasmic N-terminus, and a cytoplasmic C-terminus.

Risk of methicillin-resistant Staphylococcus aureus surgical site infection in patients with nasal MRSA colonization

BACKGROUND

Patients colonized with methicillin-resistant Staphylococcus aureus (MRSA) are at increased risk for invasive infection compared with noncolonized patients; however, the magnitude of risk for MRSA surgical site infection (SSI) is unclear. To aid in planning of infection prevention strategies, we sought to assess the incidence of MRSA SSI in MRSA carriers.

METHODS

We conducted a retrospective cohort study at our tertiary care center of inpatients who underwent MRSA polymerase chain reaction (PCR) screen of the nares within 30 days before a National Healthcare Safety Network principal procedure between April 2008 and July 2010.

RESULTS

The rate of MRSA SSI was 1.86% in the MRSA PCR-positive group (n = 431) and 0.20% in the MRSA PCR-negative group (n = 9432). Multivariate analysis identified MRSA PCR-positive status as an independent risk factor for MRSA SSI (odds ratio, 9.20; 95% confidence interval, 3.81-20.47; P < .0001); other risk factors included duration of surgery ≥137 minutes, American Society of Anesthesiologists score ≥3, and abdominal surgery.

CONCLUSIONS

Surgical patients with a positive nasal MRSA PCR screen had a 9-fold greater odds of developing a subsequent MRSA SSI compared with patients with a negative nasal MRSA PCR screen. The incidence of MRSA SSI in PCR-positive patients was low (1.86%), however, and identifying subsets of patients at greatest risk for SSI may help target decolonization and other interventions.

High-density livestock operations, crop field application of manure, and risk of community-associated methicillin-resistant Staphylococcus aureus infection in Pennsylvania

IMPORTANCE

Nearly 80% of antibiotics in the United States are sold for use in livestock feeds. The manure produced by these animals contains antibiotic-resistant bacteria, resistance genes, and antibiotics and is subsequently applied to crop fields, where it may put community members at risk for antibiotic-resistant infections.

OBJECTIVE

To assess the association between individual exposure to swine and dairy/veal industrial agriculture and risk of methicillin-resistant Staphylococcus aureus (MRSA) infection.

DESIGN, SETTING, AND PARTICIPANTS

A population-based, nested case-control study of primary care patients from a single health care system in Pennsylvania from 2005 to 2010. Incident MRSA cases were identified using electronic health records, classified as community-associated MRSA or health care-associated MRSA, and frequency matched to randomly selected controls and patients with skin and soft-tissue infection. Nutrient management plans were used to create 2 exposure variables: seasonal crop field manure application and number of livestock animals at the operation. In a substudy, we collected 200 isolates from patients stratified by location of diagnosis and proximity to livestock operations.

MAIN OUTCOMES AND MEASURES

Community-associated MRSA, health care-associated MRSA, and skin and soft-tissue infection status (with no history of MRSA) compared with controls.

RESULTS

From a total population of 446,480 patients, 1539 community-associated MRSA, 1335 health care-associated MRSA, 2895 skin and soft-tissue infection cases, and 2914 controls were included. After adjustment for MRSA risk factors, the highest quartile of swine crop field exposure was significantly associated with community-associated MRSA, health care-associated MRSA, and skin and soft-tissue infection case status (adjusted odds ratios, 1.38 [95% CI, 1.13-1.69], 1.30 [95% CI, 1.05-1.61], and 1.37 [95% CI, 1.18-1.60], respectively); and there was a trend of increasing odds across quartiles for each outcome (P ≤ .01 for trend in all comparisons). There were similar but weaker associations of swine operations with community-associated MRSA and skin and soft-tissue infection. Molecular testing of 200 isolates identified 31 unique spa types, none of which corresponded to CC398 (clonal complex 398), but some have been previously found in swine.

CONCLUSIONS AND RELEVANCE

Proximity to swine manure application to crop fields and livestock operations each was associated with MRSA and skin and soft-tissue infection. These findings contribute to the growing concern about the potential public health impacts of high-density livestock production.

Clinical significance of methicillin-resistant Staphylococcus aureus colonization on hospital admission: one-year infection risk

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among inpatients is a well-established risk factor for MRSA infection during the same hospitalization, but the long-term risk of MRSA infection is uncertain. We performed a retrospective cohort study to determine the one-year risk of MRSA infection among inpatients with MRSA-positive nasal polymerase chain reaction (PCR) tests confirmed by positive nasal culture (Group 1), patients with positive nasal PCR but negative nasal culture (Group 2), and patients with negative nasal PCR (Group 3).

METHODOLOGY/PRINCIPAL FINDINGS

Subjects were adults admitted to a four-hospital system between November 1, 2006 and March 31, 2011, comprising 195,255 admissions. Patients underwent nasal swab for MRSA PCR upon admission; if positive, nasal culture for MRSA was performed; if recovered, MRSA was tested for Panton-Valentine Leukocidin (PVL). Outcomes included MRSA-positive clinical culture and skin and soft tissue infection (SSTI). Group 1 patients had a one-year risk of MRSA-positive clinical culture of 8.0% compared with 3.0% for Group 2 patients, and 0.6% for Group 3 patients (p<0.001). In a multivariable model, the hazard ratios for future MRSA-positive clinical culture were 6.52 (95% CI, 5.57 to 7.64) for Group 1 and 3.40 (95% CI, 2.70 to 4.27) for Group 2, compared with Group 3 (p<0.0001). History of MRSA and concurrent MRSA-positive clinical culture were significant risk factors for future MRSA-positive clinical culture. Group 1 patients colonized with PVL-positive MRSA had a one-year risk of MRSA-positive clinical culture of 10.1%, and a one-year risk of MRSA-positive clinical culture or SSTI diagnosis of 21.7%, compared with risks of 7.1% and 12.5%, respectively, for patients colonized with PVL-negative MRSA (p = 0.04, p = 0.005, respectively).

CONCLUSIONS/SIGNIFICANCE

MRSA nasal colonization is a significant risk factor for future MRSA infection; more so if detected by culture than PCR. Colonization with PVL-positive MRSA is associated with greater risk than PVL-negative MRSA.

Molecular epidemiology of Staphyloccocus aureus colonization in the Old Order of Amish of Lancaster County, Pennsylvania, USA

Transmission of Staphylococcus aureus colonization in community-based populations is not well understood. We sought to describe the molecular epidemiology of S. aureus colonization in the Old Order Amish. The study was a prospective, observational study of healthy adults and their same-sex siblings who were cultured from the anterior nares twice. S. aureus isolates were characterized using spa typing. Overall, 40% (159/398) of the study population was colonized with S. aureus. There were 84 spa types with the most abundant spa types being t012 (13%) and t021 (7%). There was no clustering of spa types within sibling groups; however, there was clustering within households. There were 111 S. aureus-colonized participant pairs living within the same household. Of these, 47% had concordant spa types. The diversity of spa types across a relatively isolated, genetically homogenous population with a similar lifestyle is striking. Taken together this suggests that S. aureus transmission is a local phenomenon limited to very close contact.

Risk factors for and impact of methicillin-resistant Staphylococcus aureus nasal colonization in patients in a medical intensive care unit

This retrospective cohort study investigated the impact and predictive factors of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization in 180 patients admitted to a medical intensive care unit between July 2009 and June 2010. No significant associations between MRSA nasal colonization and the incidence of health care-associated multidrug-resistant-related infections, intensive care unit length of stay, or inpatient mortality were found. Significant risk factors for MRSA colonization included previous medical history of diabetes mellitus and congestive heart failure.