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Journal of Clinical Microbiology, April 2006, p. 1219-1223, Vol. 44, No. 4
0095-1137/06/$08.00+0 doi:10.1128/JCM.44.4.1219-1223.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Evaluation of the IDI-MRSA Assay for Detection of Methicillin-Resistant Staphylococcus aureus from Nasal and Rectal Specimens Pooled in a Selective Broth
M. Desjardins,1,2*
Christiane Guibord,2
B. Lalonde,1
B. Toye,1,2 and
K. Ramotar1,2
Division of Microbiology, Department of Pathology and Laboratory Medicine, The Ottawa Hospital,1
The Ottawa Hospital Research Institute, Ottawa, Ontario, Canada2
Received 19 December 2005/
Returned for modification 10 January 2006/
Accepted 19 January 2006
Rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) by PCR can be performed directly from nasal specimens with the IDI-MRSA assay. To improve the efficiency of screening, we evaluated the performance of the IDI-MRSA assay for the detection of MRSA from pooled and unpooled specimens cultured in a selective broth. Of the 287 specimens evaluated, 71 were culture and PCR positive, 203 were culture and PCR negative, 3 were culture positive and PCR negative, 8 were culture negative and PCR positive, and 2 remained inhibited. A methicillin-susceptible Staphylococcus aureus isolate was recovered from five of the eight specimens with false-positive PCR results. Compared to the results of culture, the sensitivity, specificity, and negative and positive predictive values of the IDI-MRSA assay for detection of MRSA from broth were 96%, 96%, 90%, and 98%, respectively. Following implementation of the IDI-MRSA assay, PCR-positive broths were subcultured for evaluation of assay performance. Of the 298 IDI-MRSA assay-positive broths, the results for 103 could not be confirmed by culture. A methicillin-susceptible S. aureus (MSSA) isolate was recovered from 77 of these 103 broths. Repeat testing by the IDI-MRSA assay directly with the MSSA isolates confirmed the original positive PCR result. The positive predictive value of the IDI-MRSA assay fell from 90% during the evaluation phase to 65% postimplementation. The IDI-MRSA assay performed well for the detection of MRSA from a selective broth compared to the performance of the detection of MRSA from culture. However, because of the burden associated with implementation of infection control precautions, cultures remain essential in confirming positive IDI-MRSA results.
* Corresponding author. Mailing address: Division of Microbiology, The Ottawa Hospital, 501 Smyth Rd., Ottawa, Ontario K1H 8L6, Canada. Phone: (613) 737-8899, ext. 72242. Fax: (613) 737-8324. E-mail:
madesjardins{at}ottawahospital.on.ca.
Journal of Clinical Microbiology, April 2006, p. 1219-1223, Vol. 44, No. 4
0095-1137/06/$08.00+0 doi:10.1128/JCM.44.4.1219-1223.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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