Carol Young

Comparison of Chromogenic Media to BD GeneOhm Methicillin-Resistant Staphylococcus aureus (MRSA) PCR for Detection of MRSA in Nasal Swabs

ABSTRACT To select a method for detecting methicillin-resistant Staphylococcus aureus (MRSA) in nasal swabs, we compared BD GeneOhm MRSA PCR and various culture media (mannitol salt agar with cefoxitin, MRSASelect, CHROMagar MRSA, and Spectra MRSA). While PCR detection of MRSA was more rapid, MRSASelect and Spectra MRSA demonstrated performance equivalent to that of PCR with maximal detection at 24 h.

Clinical and Laboratory Features of Streptococcus salivarius Meningitis: A Case Report and Literature Review

Streptococcus salivarius is a normal member of the human oral microbiome that is an uncommon cause of invasive infections. Meningitis is a rare but increasingly reported infection caused by S. salivarius. Despite the growing number of reported cases, a comprehensive review of the literature on S. salivarius meningitis is lacking. We sought to gain a better understanding of the clinical presentation, evaluation, management, and outcome of S. salivarius meningitis by analyzing previously reported cases. In addition to a single case reported here, 64 previously published cases of meningitis were identified for this review. The collected data confirm that most patients presented with classical signs and symptoms of bacterial meningitis with a predominance of neutrophils in the cerebrospinal fluid (CSF) and hypoglycorrhachia. The majority of cases followed iatrogenic or traumatic CSF contamination. Most cases were diagnosed by CSF culture within one day of symptom onset. There was no clear evidence of predisposing co-morbid conditions in patients with meningitis, although in most case reports, limited information was given on the medical history of each patient. Outcomes were generally favorable with antibiotic management. Clinicians should suspect S. salivarius meningitis in patients presenting acutely after medical or surgical procedures involving the meninges.

Multicenter Clinical Evaluation of VRESelect Agar for Identification of Vancomycin-Resistant Enterococcus faecalis and Enterococcus faecium

ABSTRACT A chromogenic medium for identification of vancomycin-resistant Enterococcus faecalis and Enterococcus faecium, VRESelect, was compared to bile esculin azide agar with 6 μg/ml vancomycin (BEAV) for the isolation of vancomycin-resistant enterococci (VRE) from stool specimens. At 24 to 28 h, VRESelect demonstrated 98.7% (confidence interval [CI], 96.1 to 99.7%) sensitivity and 99.0% (CI, 98.0 to 99.6%) specificity versus 85.1% (CI, 79.8 to 89.5%) and 90.1% (CI, 79.8 to 89.5%) sensitivity and specificity, respectively, for BEAV.

Culture-Based Method with Performance Comparable to That of PCR-Based Methods for Detection of Group B Streptococcus in Screening Samples from Pregnant Women

ABSTRACT We compared five approaches for group B streptococcus (GBS) detection: three culture-based methods and two methods using broth-enhanced real-time PCR. Carrot broth-enhanced subculture to GBS Detect (Hardy Diagnostics, Santa Maria, CA) exhibited sensitivity and specificity comparable to carrot broth- and LIM broth-enhanced real-time PCRs.

Diagnosis of Clostridium difficile infection: Comparison of four methods on specimens collected in Cary-Blair transport medium and tcdB PCR on fresh versus frozen samples

Clostridium difficile infection (CDI) caused by toxigenic strains of C. difficile is primarily a nosocomial infection with increasing prevalence. Stool specimens are typically collected in Cary-Blair transport medium to maximize culture-based detection of common stool pathogens. The goal of this study was to establish an analytically accurate and efficient algorithm for the detection of CDI in our patient population using samples collected in Cary-Blair transport medium. In addition, we wished to determine whether the sensitivity and specificity of PCR was affected by freezing samples before testing. Using 357 specimens, we compared four methods: enzyme immunoassay for the antigen glutamate dehydrogenase (Wampole™ C. DIFF CHEK-60 Assay, GDH), toxin A and B enzyme immunoassay (Remel ProSpecT™ C. difficile Toxin A/B Microplate Assay, Toxin EIA), cell culture cytotoxicity neutralization assay (Bartels™ Cytotoxicity Assay, CT), and real-time PCR targeting the toxin B gene (BD GeneOhm™ Cdiff Assay, PCR). The analytic sensitivity and specificity of each as determined using a combined gold standard were as follows: GDH, 100% and 93.2%; Toxin EIA, 82.9% and 82.9%; CT, 100% and 100%; PCR (performed on frozen specimens) 74.3% and 96.6%; respectively. However, the sensitivity and specificity of PCR improved to 100% when performed on 50 fresh stool samples collected in Cary-Blair. While CT remains a sensitive method for the detection of CDI, GDH offers an excellent initial screening method to rule out CDI. While the performance of each assay did not appear to be affected by collection in Cary-Blair medium, PCR performed better using fresh specimens.

In Vitro Activity of Ceftolozane-Tazobactam and Other Antimicrobial Agents against Burkholderia cepacia Complex and Burkholderia gladioli

ABSTRACT We tested the activities of ceftolozane-tazobactam and 13 other antimicrobial agents against 221 strains of Burkholderia cepacia complex and Burkholderia gladioli. Most strains (82%) were cultured from persons with cystic fibrosis, and most (85%) were recovered since 2011. The ceftolozane-tazobactam MIC was ≤8 μg/ml for 77% of the strains. However, the MIC range was broad (≤0.5 to >64 μg/ml; MIC50/90, 2/32 μg/ml). Significant differences in susceptibility to some antimicrobial agents were observed between species.

Multicenter Evaluation of MRSASelect II Chromogenic Agar for Identification of Methicillin-Resistant Staphylococcus aureus from Wound and Nasal Specimens

ABSTRACT Hospitals strive to reduce methicillin-resistant Staphylococcus aureus (MRSA) prevalence via active surveillance of inpatient populations. Rapid and inexpensive screening methods are utilized when molecular methods are not operationally feasible. In this multisite clinical trial, the utility of Bio-Rads MRSASelect II was evaluated for MRSA identification from remnant nares and wound swabs. The prevalence of MRSA was 11.1% (n = 1,384) from nares samples and 18.1% (n = 842) from wound samples. MRSASelect II had an overall concordance of 95.4% (confidence interval [CI] = 94.5% to 96.2%) compared to a broth-enriched reference standard. Comparisons between results, stratified by examination times, exhibited a nonsignificant trend toward increased positivity at prolonged incubation times. Cefoxitin screening of colonies directly from MRSASelect II was 96.7% (95.8% to 97.3%) concordant compared to testing of colonies following broth enrichment. A comparison of MRSASelect and MRSASelect II revealed no statistical differences; however, the latter exhibited earlier positivity, greater selectivity, and more intense indicator staining, which resulted in facilitated differentiation of positive results. MRSASelect II agar is a simple, rapid, and robust method to routinely screen patients for MRSA colonization without the need for additional testing.

The Nose Knows Not: Poor Predictive Value of Stool Sample Odor for Detection of Clostridium difficile

To the Editor—Clostridium difficile infection (CDI) is a nosocomial infection that poses a challenge to infection control procedures, often from delays in testing [1]. A nurse-driven protocol may result in earlier identification and isolation of infected patients, leading to decreased transmission. It is a common “urban legend” among nursing staff that they can identify patients with CDI by the odor of their stool alone. Based on studies that used gas chromatography, this is biologically plausible—in 2004, Probert et al demonstrated the presence of unique volatile organic compounds (VOCs) in stool from patients with CDI [2]. Similarly, Garner et al demonstrated in 2007 that derived discriminant scores from VOC data had 100% predictive accuracy in distinguishing stool from patients who were asymptomatic, had ulcerative colitis, had Campylobacter jejuni infection, or had CDI [3]. In 2002, Johansen et al found that nurses on the wards were 84% sensitive and 77% specific in diagnosing CDI by stool odor [4]. Similarly, in 2007 Burdette et al found that nurses were 55% sensitive and 83% specific in diagnosing CDI [5]. A limitation of both studies, as pointed out in an accompanying commentary [6], is that the nurses were not blinded to any patient characteristics. Thus, one could not conclude that stool odor was the sole factor informing their assessments. We hypothesized that nurses can detect the presence of C. difficile in stool by odor alone in a controlled, laboratory setting. Nurses were recruited from inpatient wards at our hospital. Our microbiology laboratory randomly set aside 5 positive and 5 negative stool samples based on results from 2-step testing (glutamate dehydrogenase/toxin enzyme immunoassay followed by polymerase chain reaction for discordant results) for C. difficile toxin (CDTOX) from patients with liquid stool. We asked nurses about their work experience and whether they believed they could detect C. difficile by odor. They were instructed to sniff each sample and record whether CDTOX positive stool was present. Fisher exact and Mann-Whitney tests were used to assess statistical significance. Eighteen nurses participated. Experience ranged from 1 to 30 years (8 with >10 years of experience). Eleven felt confident in their sniffing ability (61%). The median percentage correct was 45% (range, 40%–80%). CDTOX-positive samples elicited a lower percentage of correct answers than CDTOX-negative samples (Figure ​(Figure11A; median, 31% vs 74%; P = .0119). No single individual performed better than chance (mean sensitivity/specificity = 0.26/0.69). Those with confidence in sniffing did not perform better than others (Figure ​(Figure11B; median, 40% vs 50%; P = .2471) and more experienced nurses were no different from less experienced nurses (Figure ​(Figure11C; both 45%; P = .8887). Figure 1. The percentage of correct responses, based on smell, regarding the presence of toxigenic Clostridium difficile in stool depending on sample type (A), confidence level (B), and experience (C); lines are at the median and interquartile range. Abbreviation: ... In this controlled laboratory setting, our nurses were unable to identify stool samples with C. difficile by odor, but CDTOX-negative samples elicited more correct answers than CDTOX-positive samples. More experience with nursing and confidence in sniffing ability did not improve performance. It is likely that our findings differ from prior studies owing to their inadequate blinding of nurses to patient and stool characteristics.

Bacterial Contamination of CT Equipment

RATIONALE AND OBJECTIVE This study aimed to evaluate the use of an adenosine triphosphate (ATP) monitoring system to minimize surface contamination on inpatient computed tomography (CT) scanners. METHODS The bore, table, and wrap of two quaternary care inpatient CT scanners (load/scanner: ~ 30-40 CT examinations/day) were assayed with bacterial cultures and an ATP detection system during six prospective iterative plan-do-check-act improvement cycles from January 6, 2016 to October 12, 2016. Per-cycle sampling was for eight consecutive weekdays. ATP detection was expressed as relative light units (RLUs) through a luciferase reaction, with >350 RLU considered contaminated per manufacturer recommendations. Culture swabs were placed into 6.5% NaCl broth, a Staphylococcus enrichment broth, and incubated aerobically at 37°C for 48 hours. Positive broths were plated to chromogenic Staphylococcus media. Culture rates (Fisher exact test) and RLU values (Mann-Whitney U test) were compared. RESULTS In Cycle 1, both culture results and median RLU values indicated the wrap was the most contaminated item (positive culture rate: 63% [10/16], median RLU interquartile range: 173 [IQR: 56-640]); however, RLU values were not predictive of per-sample culture results (P = .36). Following iterative improvements, RLU values at Cycle 6 were significantly lower than at peak (P = .02-.04) and within manufacturers recommendations: all samples: 45 (IQR: 16-87), bore: 26 (IQR: 0-51), table: 68 (IQR: 21-89), wrap: 47 (IQR: 38-121). CONCLUSION The Velcro wrap is the most contaminated item on a CT scanner, and special processes may be needed to ensure adequate cleansing. ATP detection is a crude surrogate for bacterial culture results but benefits from speed, reduced cost, and greater statistical power.