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ABSTRACTOur three-hospital system began active surveillance for methicillin-resistant Staphylococcus aureus(MRSA) nasal colonization, with decolonization of positive patients, on all admissions starting 1 August 2005. A question not previously addressed is whether reduction of the incidence of MRSA disease would lower the total number of S. aureusclinical isolates recovered by the microbiology laboratory that are reported to health care providers. The decreases in the numbers of MRSA and total S. aureusclinical isolates for each year after August 2005 were highly statistically significant compared to the numbers in each of the prior 3 years (P< 0.0001).

ABSTRACTWe evaluated the use of the BD GeneOhm MRSA real-time PCR assay (BD Diagnostics, San Diego, CA) for the detection of nasal colonization with methicillin-resistant Staphylococcus aureus(MRSA). The initial evaluation consisted of 403 paired nasal swabs and was done using the specimen preparation provided with the kit and an in-house lysis method that was specifically developed to accommodate large-volume testing using a minimal amount of personnel time. One swab was placed in an achromopeptidase (ACP) lysis solution, and the other was first used for culture and then prepared according to the kit protocol. PCR was performed on both lysates, and results were compared to those for culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the PCR assay were 98%, 96%, 77%, and 99.7% with the kit lysate and 98%, 95%, 75%, and 99.7% with the ACP lysate (P, not significant), respectively. The second evaluation was done after implementation of all-admission surveillance using PCR with ACP lysis and a sampling of 1,107 PCR-negative samples and 215 PCR-positive samples that were confirmed by culture. The results of this sampling showed an NPV of 99.9% and a PPV of 73.5% (prevalence, 6%), consistent with our initial findings. The BD GeneOhm MRSA assay is an accurate and rapid way to detect MRSA nasal colonization. When one is dealing with large specimen numbers, the ACP lysis method offers easier processing without negatively affecting the sensitivity or specificity of the PCR assay.

Nasal carriage of Staphylococcus aureusis considered a source of subsequent infection in health care settings. Utilization of real-time polymerase chain reaction (PCR) for detection of S. aureushas the potential to dramatically affect infection control practice by rapidly identifying S. aureus-colonized patients. We developed and validated the use of real-time PCR for detection of S. aureuscolonization in two patient populations. Paired nasal swabs were collected from 299 neonates and from 151 adult patients at Evanston Hospital. One swab was used for culture and the other placed into a bacterial lysis solution containing achromopeptidase. The DNA liberated was used as the template for real-time PCR with primers for the femAgene. SYBR Green was used for amplicon detection. In the neonatal population the sensitivity, specificity, predictive value positive and predictive value negative for culture and PCR was 92%versus96%, 100%versus100%, 100%versus100%, and 98%versus99%, respectively. In the adults the results were 90%versus100%, 100%versus98%, 100%versus96%, and 95%versus100%, respectively. Real-time PCR was able to detect S. aureusin 2 hours compared to 1 to 4 days for culture and provided sensitivity equal to or greater than culture.

ABSTRACTWe surveyed environmental surfaces in our clinical microbiology laboratory to determine the prevalence of vancomycin-resistant enterococci (VRE) and multidrug-resistantEnterobacteriaceae(MDRE) during a routine working day. From a total of 193 surfaces, VRE were present on 20 (10%) and MDRE were present on 4 (2%) of the surfaces tested. In a subsequent survey after routine cleaning, all of the 24 prior positive surfaces were found to be negative. Thus, those in the laboratory should recognize that many surfaces may be contaminated by resistant organisms during routine processing of patient specimens.

ABSTRACTCommunity-acquired MRSA (CA-MRSA) is potentially a new emerging pathogen with most strains susceptible to many antimicrobials except for ß-lactam antibiotics. We retrospectively reviewed MRSA isolates during a 20-month study period (January 1998 through August 1999) and investigated those that were clindamycin susceptible. Patients were not considered to harbor CA-MRSA if they had been admitted to a hospital within the preceding 2 years or if their isolate had been obtained more than 72 h after admission. There were 2,817 S. aureusisolates, with 1,071 (38%) being MRSA. Of these 1,071 isolates, 161 were clindamycin susceptible; these were recovered from 81 patients. Of these 81 patients, 20 appeared to have community-acquired strains, but only 2 could be confirmed as having CA-MRSA.

ABSTRACTIt has been suggested that a method of performing surveillance for vancomycin-resistant enterococci (VRE) is to screen specimens submitted for Clostridium difficiletesting. We compared this approach to our focused surveillance program of high-risk units during October 1997 to compare the yield of VRE and multidrug-resistantEnterobacteriaceae(MDRE) with both methods. Of the stools submitted for C. difficiletesting, 14% were positive for VRE or MDRE, whereas rectal swabs from routine surveillance yielded 11% VRE- or MDRE-positive results. Although stools submitted forC. difficiletesting resulted in a higher percentage of positive cultures, 14 VRE- and 2 MDRE-positive patients from our high-risk population were missed because many patients had no stool submitted for C. difficiletesting. Therefore, while screening stools submitted for C. difficiletesting cannot replace our focused surveillance program, it appears advantageous to assess these stools at various intervals to detect new patient reservoirs of drug-resistant organisms that may benefit from routine surveillance cultures.

ABSTRACTWe compared the Rodac imprint technique to selective enrichment broth for detecting vancomycin-resistant enterococci (VRE) and multidrug-resistant Enterobacteriaceae(MDRE) on surfaces. Rodac plates contained tryptic soy agar with 5% sheep blood, vancomycin (6 µg/ml), ceftazidime (2 µg/ml), amphotericin B (2 µg/ml), and clindamycin (1 µg/ml). Two types of broth were used: brain heart infusion (BHI) and BHI plus vancomycin (6 µg/ml) and ceftazidime (2 µg/ml) (BHIVC). Of the 46 surfaces cultured for VRE, 12 (26%) were positive. Of the 12 VRE-positive surfaces, 11 (92%) grew from Rodac, 8 (67%) grew from BHIVC, and 7 (58%) grew from BHI. A larger study is needed for MDRE, as only 4 of 43 surfaces were MDRE positive. The Rodac imprint technique successfully recovered VRE from environmental surfaces.

ABSTRACTA real-time PCR assay was developed targeting the blaKPCresponsible for Klebsiella pneumoniaecarbapenemase (KPC)-mediated carbapenem resistance and was validated for testing colonies or enrichment broth cultures. The assay accurately detects KPC-containing strains with high analytical specificity and sensitivity.