Tracy Ross

Yield of stool culture with isolate toxin testing versus a two-step algorithm including stool toxin testing for detection of toxigenic Clostridium difficile.

ABSTRACT We examined the incremental yield of stool culture (with toxin testing on isolates) versus our two-step algorithm for optimal detection of toxigenic Clostridium difficile. Per the two-step algorithm, stools were screened for C. difficile-associated glutamate dehydrogenase (GDH) antigen and, if positive, tested for toxin by a direct (stool) cell culture cytotoxicity neutralization assay (CCNA). In parallel, stools were cultured for C. difficile and tested for toxin by both indirect (isolate) CCNA and conventional PCR if the direct CCNA was negative. The “gold standard” for toxigenic C. difficile was detection of C. difficile by the GDH screen or by culture and toxin production by direct or indirect CCNA. We tested 439 specimens from 439 patients. GDH screening detected all culture-positive specimens. The sensitivity of the two-step algorithm was 77% (95% confidence interval [CI], 70 to 84%), and that of culture was 87% (95% CI, 80 to 92%). PCR results correlated completely with those of CCNA testing on isolates (29/29 positive and 32/32 negative, respectively). We conclude that GDH is an excellent screening test and that culture with isolate CCNA testing detects an additional 23% of toxigenic C. difficile missed by direct CCNA. Since culture is tedious and also detects nontoxigenic C. difficile, we conclude that culture is most useful (i) when the direct CCNA is negative but a high clinical suspicion of toxigenic C. difficile remains, (ii) in the evaluation of new diagnostic tests for toxigenic C. difficile (where the best reference standard is essential), and (iii) in epidemiologic studies (where the availability of an isolate allows for strain typing and antimicrobial susceptibility testing).

An Evaluation of Environmental Decontamination With Hydrogen Peroxide Vapor for Reducing the Risk of Patient Acquisition of Multidrug-Resistant Organisms

BACKGROUND Admission to a room previously occupied by a patient with certain multidrug-resistant organisms (MDROs) increases the risk of acquisition. Traditional cleaning strategies do not remove all environmental MDROs. We evaluated the environmental and clinical impact of hydrogen peroxide vapor (HPV) room disinfection. METHODS We performed a 30-month prospective cohort intervention study on 6 high-risk units in a 994-bed tertiary care hospital. Following a 12-month preintervention phase, HPV was implemented on 3 units to decontaminate the rooms of patients known to be infected or colonized with epidemiologically important MDROs, following their discharge. Monthly environmental samples for MDROs were collected on all study units for 3 preintervention and 6 intervention months. The risk of MDRO acquisition in patients admitted to rooms decontaminated using HPV was compared with rooms disinfected using standard methods. RESULTS The prior room occupant was known to be infected or colonized with an MDRO in 22% of 6350 admissions. Patients admitted to rooms decontaminated using HPV were 64% less likely to acquire any MDRO (incidence rate ratio [IRR], 0.36; 95% confidence interval [CI], .19-.70; P < .001) and 80% less likely to acquire VRE (IRR, 0.20; 95% CI, .08-.52; P < .001) after adjusting for other factors. The risk of acquiring Clostridium difficile, methicillin-resistant Staphylococcus aureus, and multidrug-resistant gram-negative rods individually was reduced, but not significantly. The proportion of rooms environmentally contaminated with MDROs was reduced significantly on the HPV units (relative risk, 0.65, P = .03), but not on non-HPV units. CONCLUSIONS HPV decontamination reduced environmental contamination and the risk of acquiring MDROs compared with standard cleaning protocols.

A Prospective Study to Determine Whether Cover Gowns in Addition to Gloves Decrease Nosocomial Transmission of Vancomycin-Resistant Enterococci in an Intensive Care Unit

BACKGROUND Vancomycin-resistant enterococci (VRE) remain a significant nosocomial pathogen. Current guidelines of the Hospital Infection Control Practices Advisory Committee (HICPAC) of the Centers for Disease Control and Prevention (CDC) recommend the use of gowns and gloves for some interactions with VRE-infected or -colonized patients to prevent nosocomial transmission of VRE. OBJECTIVE To assess the effect of disposable cover gowns on preventing nosocomial transmission of VRE. DESIGN AND SETTING Prospective study in a 16-bed medical intensive care unit of a university teaching hospital. PATIENTS All patients who were at risk to acquire VRE, were admitted to the intensive care unit from August 1998 to January 1999, and had at least two perirectal cultures were included in the analysis of VRE acquisition. INTERVENTION VRE isolation precautions were changed from gowns and gloves to gloves alone. MAIN OUTCOME risk factors for VRE acquisition. RESULTS The VRE acquisition rate was 1.80 cases per 100 days at risk in the gown and gloves period compared with 3.78 in the gloves only period (P = .04). In a proportional hazards model adjusted for length of stay, gloves only precautions with a hazard ratio of 2.5 (P = .02; 95% confidence interval, 1.2 to 5.3) were the only independent risk factor for VRE acquisition. CONCLUSION Our data lend support to current HICPAC recommendations for the use of cover gowns to decrease nosocomial transmission of VRE.

Comparison of an Automated Repetitive Sequence-Based PCR Microbial Typing System to Pulsed-Field Gel Electrophoresis for Analysis of Outbreaks of Methicillin-Resistant Staphylococcus aureus

ABSTRACT Rapid and sensitive methods for accurate strain delineation are essential for monitoring and preventing transmission of methicillin-resistant Staphylococcus aureus (MRSA). Pulsed-field gel electrophoresis (PFGE) has been the standard technique for strain typing most bacterial species including MRSA. The goal of this study was to compare the performance of the DiversiLab microbial typing system (Bacterial BarCodes, Inc., Houston, TX) (rep-PCR) to that of PFGE for typing MRSA isolates from five well-defined outbreaks. The DiversiLab rep-PCR assay is a rapid, semiautomated method based on PCR amplification of specific regions between noncoding repetitive sequences in the bacterial genome. rep-PCR was performed according to the manufacturers recommendations, and the results were analyzed and dendrograms were generated using the DiversiLab analysis software (version 2.1.66a). PFGE was performed and interpreted according to published procedures. rep-PCR results using similarity indices (SI) of 80%, 85%, and 90% were compared to PFGE analysis. In addition, intra- and interrun reproducibility was determined for rep-PCR. Overall, correct assignment to outbreak versus nonoutbreak clusters occurred for 91 of 109 isolates (85% agreement) when using a SI of 85%. For each specific outbreak, concordance between rep-PCR and PFGE ranged from 73% to 100%. There were 18 discrepant results (17%). Fourteen isolates were unique by PFGE, but they were placed in clusters by rep-PCR; the other 4 were placed in clusters different from those assigned by PFGE. Intra- and interrun reproducibility was excellent. Times to results were 12 to 24 h for rep-PCR compared to 2 to 4 days for PFGE. Rapid, standardized results and excellent reproducibility make rep-PCR a valuable tool for use in MRSA investigations. However, since rep-PCR was less discriminatory than PFGE, we recommend that it be used to screen isolates, followed by testing isolates which share the same rep-PCR pattern with a more sensitive method, such as PFGE or multilocus sequence typing.

Comparison of the BD GeneOhm Methicillin-Resistant Staphylococcus aureus (MRSA) PCR Assay to Culture by Use of BBL CHROMagar MRSA for Detection of MRSA in Nasal Surveillance Cultures from an At-Risk Community Population

ABSTRACT We compared the BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) PCR assay to culture with BBL CHROMagar MRSA for nasal surveillance among 602 arrestees from the Baltimore City Jail. The sensitivity and specificity were 88.5% and 91.0%, respectively, and after secondary analysis using enrichment broth, they were 89.0% and 91.7%, respectively. Twenty-three of 42 false-positive PCR lysates contained methicillin-susceptible S. aureus.

Outbreak of multidrug-resistant Serratia marcescens infection in a neonatal intensive care unit.

BACKGROUND Serratia marcescens causes healthcare-associated infections and significant morbidity and mortality in neonatal intensive care units (NICUs). We report the investigation and control of an outbreak of multidrug-resistant (MDR) S. marcescens infection at an NICU. METHODS An outbreak investigation and a case-control study were undertaken at a 36-bed NICU in a tertiary care hospital in Baltimore, Maryland, for the period from October 2004 through February 2005. The outbreak investigation included case identification, review of medical records, environmental cultures, patient surveillance cultures, personnel hand cultures, and pulsed-field gel electrophoresis (PFGE). The case-control study included case identification and review of medical records. Infection control measures were implemented. Eighteen NICU neonates had cultures that grew MDR S. marcescens during the study period. The case-control study included 16 patients with the outbreak strain or an unidentified strain of MDR S. marcescens and 32 control patients not infected and/or colonized with MDR S. marcescens, treated in the NICU for at least 48 hours during the study period. RESULTS PFGE analysis identified a single strain of MDR S. marcescens that infected or colonized 15 patients. Two patients had unique strains, and 1 patients isolate could not be subtyped. An unrelated MDR S. marcescens isolate was recovered from a sink drain. Exposure to inhalational therapy was an independent risk factor for MDR S. marcescens acquisition after adjusting for birth weight. Extensive investigation failed to reveal a point source for the outbreak. CONCLUSION A single epidemic strain of MDR S. marcescens spread rapidly and threatened to become endemic in this NICU. Transient carriage on the hands of healthcare personnel or on respiratory care equipment was the likely mode of transmission. Cohorting patients and staff, at the cost of bed closures and additional personnel, interrupted transmission and halted the outbreak.

Rapid Molecular Genotyping and Clonal Complex Assignment of Staphylococcus aureus Isolates by PCR Coupled to Electrospray Ionization-Mass Spectrometry

ABSTRACT We describe a high-throughput assay using PCR coupled to electrospray ionization-mass spectrometry (PCR/ESI-MS) to determine the genotypes of Staphylococcus aureus isolates. The primer sets used in the PCR/ESI-MS assay were designed to amplify the same genes analyzed in multilocus sequence typing (MLST). The method was used to identify the clonal complex and USA type of each isolate and is suitable for use in a clinical or public-health setting. The method was validated using a panel of diverse isolates from the Centers for Disease Control and Prevention that were previously characterized by MLST and pulsed-field gel electrophoresis (PFGE). Clinical isolates from two geographically distinct hospitals were characterized, and the clustering results were in agreement with those for repetitive-element PCR and PFGE. The PCR/ESI-MS method enables genotyping of over 180 samples of S. aureus per day in an automated fashion.

Methicillin-Resistant Staphylococcus aureus Colonization and Risk of Subsequent Infection in Critically Ill Children: Importance of Preventing Nosocomial Methicillin-Resistant Staphylococcus aureus Transmission

BACKGROUND Methicillin-resistant Staphylococcus aureus (MRSA) colonization is a predictor of subsequent infection in hospitalized adults. The risk of subsequent MRSA infections in hospitalized children colonized with MRSA is unknown. METHODS Children admitted to an academic medical centers pediatric intensive care unit between March 2007 and March 2010 were included in the study. Anterior naris swabs were cultured to identify children with MRSA colonization at admission. Laboratory databases were queried and National Healthcare Safety Network definitions applied to identify patients with MRSA infections during their hospitalization or after discharge. RESULTS The MRSA admission prevalence among 3140 children was 4.9%. Overall, 56 children (1.8%) developed an MRSA infection, including 13 (8.5%) colonized on admission and 43 (1.4%) not colonized on admission (relative risk [RR], 5.9; 95% confidence interval [CI], 3.4-10.1). Of those, 10 children (0.3%) developed an MRSA infection during their hospitalization, including 3 of 153 children (1.9%) colonized on admission and 7 of 2987 children (0.2%) not colonized on admission (RR, 8.4; 95% CI, 2.7-25.8). African-Americans and those with public health insurance were more likely to get a subsequent infection (P < .01 and P = .03, respectively). We found that 15 children acquired MRSA colonization in the pediatric intensive care unit, and 7 (47%) developed a subsequent MRSA infection. CONCLUSIONS MRSA colonization is a risk factor for subsequent MRSA infection in children. Although MRSA colonized children may have lower risks of subsequent infection than adults, children who acquire MRSA in the hospital have similarly high rates of infection. Preventing transmission of MRSA in hospitalized children should remain a priority.

First NDM-Positive Salmonella sp. Strain Identified in the United States

Antimicrobial resistance among Enterobacteriaceae is growing, largely due to β-lactamase production.…

A 17-MONTH EVALUATION OF A CHLORINE DIOXIDE WATER TREATMENT SYSTEM TO CONTROL LEGIONELLA SPECIES IN A HOSPITAL WATER SUPPLY

OBJECTIVE To assess the safety and efficacy of a chlorine dioxide water treatment system in controlling Legionella in a hospital water supply. DESIGN For 17 months following installation of the system, we performed regular water cultures throughout the building, assessed chlorine dioxide and chlorite levels, and monitored metal corrosion. RESULTS Sites that grew Legionella species decreased from 41% at baseline to 4% (P = .001). L. anisa was the only species recovered and it was found in samples of both hot and cold water. Levels of chlorine dioxide and chlorite were below Environmental Protection Agency (EPA) limits for these chemicals in potable water. Further, enhanced carbon filtration effectively removed the chemicals, even at chlorine dioxide levels of more than twice what was used to treat the water. After 9 months, corrosion of copper test strips exposed to the chlorine dioxide was not higher than that of control strips. During the evaluation period, there were no cases of nosocomial Legionella in the building with the system, whereas there was one case in another building. CONCLUSIONS Our results indicate that operation of a chlorine dioxide system effectively removed Legionella species from a hospital water supply. Furthermore, we found that the system was safe, as levels of chlorine dioxide and chlorite were below EPA limits. The system did not appear to cause increased corrosion of copper pipes. Our results indicate that chlorine dioxide may hold promise as a solution to the problem of Legionella contamination of hospital water supplies.