Comparison of the Velogene Rapid MRSA Identification Assay, Denka MRSA-Screen Assay, and BBL Crystal MRSA ID System for rapid identification of methicillin-resistant Staphylococcus aureus.

Early detection of methicillin-resistant S.aureus (MRSA) is critical for both the management of infected patients, and the timely institution of appropriate infection control measures. Although detection of the mecA gene by PCR remains the gold standard, this technology is inaccessible for many laboratories. Therefore, we sought to evaluate several new rapid identification systems and compare them to PCR. A total of 71 methicillin-susceptible S. aureus (MSSA), 25 borderline oxacillin-resistant S. aureus (BORSA), and 213 MRSA were selected for study. S.aureus was identified using standard methods. Initial screening was performed on a Mueller-Hinton agar plate with 6 mg/L of oxacillin. MRSA strains were identified using PCR with primers specific for the mecA gene. PCR was used as the reference method. All isolates were tested using the BBL Crystal MRSA ID System (Becton Dickinson Microbiology Systems, Maryland, USA), the MRSA-Screen Assay (Denka Seiken Co., Ltd., Tokyo, Japan), and the Velogene Rapid MRSA Identification Assay (ID Biomedical Corp, Vancouver, BC). With minor modifications, all assays were performed according to manufacturers' instructions. Overall, the 3 commercial assays performed well. The sensitivity and specificity of the BBL, Denka, and Velogene systems were 99%/100%, 99%/100%, and 96%/100% respectively. The advantages of the phenotypic tests-BBL Crystal Kit and Denka MRSA-Screen Assay include lower cost per test, shelf-life, ease of use, and rapid turn-around times. Advantages of the Velogene Rapid MRSA include ability to perform genotypic high-volume testing without the equipment requirements and technical complexity involved with PCR. Turn-around times ranged from 15 min for the Denka MRSA-Screen Assay, 2 h for the Velogene Rapid MRSA, and 4 h for the BBL Crystal. The BBL Crystal, Denka MRSA-Screen, and Velogene Rapid MRSA identification systems are rapid, easy to perform, and provide accurate identification of MRSA. These rapid kits offer an acceptable alternative for smaller, non-reference, laboratories and reduce the dependency on PCR in larger laboratories for routine confirmation.

Intra and inter technologist variability in the quality assessment of respiratory tract specimens.

The majority of microbiology laboratories have implemented quality improvement procedures such as a Q scoring system to assess the nature of clinical specimens. Our study reviewed the sources and the amount of variation when Q scoring of lower respiratory secretions was performed. In total, 450 slides representing lower respiratory tract secretions were Q scored by three experienced technologists. Total agreement regarding the number of neutrophils, squamous epithelial cells and Q scores was 76%, 57% and 57% respectively. The major factor influencing Q score values was the enumeration of epithelial cells. From our findings, we expect that there is greater variability in Q scoring then is generally acknowledged and there is a substantial degree of subjectivity on part of individual technologists reading gram stains.

Evaluation of four commercial transport media for the survival of Neisseria gonorrhoeae.

We evaluated four commercial transport systems with a standardized inoculum of clinical isolates of N. gonorrhoeae (NG), and assessed survival after holding for up to 48 hours at both ambient and refrigeration temperatures. Suspensions of clinical isolates of NG were standardized and adsorbed onto four transport swab types: Culturette EZ (Becton Dickinson [BD], Cockeysville, MD, USA); Cultureswab (Difco Laboratories, Detroit, MI, USA); Venturi Transystem (Copan Italia, Bovezzo, Italy); and a recently modified Starswab (Starplex Scientific, Etobicoke, ON). Swabs were plated to chocolate agar at 0, 6, 24, and 48 hours, and colonies counted. Each swab type was tested in quadruplicate with each NG strain for all time and temperature variables. There was a marked reduction in NG CFUs after only 6 hours incubation with each of the swabs tested. Survival was best using Venturi Transystem and Cultureswab transports (colony counts were reduced to 15.3% and 13.0%, respectively, at 6 hours) when compared with the Culturette EZ and Starswab (colony counts were reduced to 2.2% and 4.3%, respectively, at 6 hours). After the 24-hour holding period, 94% of the cultures from the Venturi Transystem were positive, 82% from the Cultureswab, 24% from the Starswab; and 17% from the Culturette EZ. After 48 hours, recovery dropped to 72%, 43%, 14%, and 0.04%, respectively. All of the systems tested had at least an 80% decrease in recovered colonies after only 6 hours. Further studies are required to determine how poor transport conditions influence the number of positive cultures and what the public health implications are. Of the swabs tested, Cultureswab and Venturi Transystem were most acceptable.

Cumulative yield from patient surveillance cultures for methicillin-resistant Staphylococcus aureus during a hospital outbreak.

The cumulative yield from cultures of separate sites was determined during the investigation of a methicillin-resistant Staphylococcus aureus (MRSA) outbreak. Surveillance cultures were submitted from clinical sites, nose, groin, and axilla of 421 patients on two different occasions. MRSA was recovered most often from various clinical sites, including lower respiratory tract, surgical wounds, urinary tract, and decubitus ulcers (total, 13 patients). Four additional patients were identified as positive from the first nasal swab, one patient from the second nasal swab, and two others from swabs of the groin. The submission of axillary swabs or a second groin swab did not identify additional MRSA-colonized patients and resulted in additional costs of $4,525.