Background:The effect of large-scale expanded surveillance for methicillin-resistant Staphylococcus aureus (MRSA) on health careassociated MRSA disease is not known.

With an assay turnaround time of <4 h, real-time PCR is a more sensitive and equally rapid test, compared with enzyme immunoassay, and is a feasible laboratory option to replace enzyme immunoassay for toxigenic C. difficile detection in clinical practice, as well as for use during the development of new therapeutic agents.

Surgical site infections (SSIs) with Staphylococcus aureus are a recognized adverse event of hip and knee replacements. We evaluated the impact of a program to detect S. aureus nasal carriers before surgery with preoperative decolonization (using mupirocin twice daily for 5 days prior to surgery) of carriers. Nasal swab samples were obtained from patients prior to surgery from 8/1/2003 through 2/28/2005. Samples were tested using real-time PCR technology to detect S. aureus. The group that developed S. aureus SSI was compared to a combined concurrent and historical control for one year following the operation. S. aureus caused 71% of SSIs in the combined control groups. Of the 1495 surgical candidates evaluated, 912 (61.0%) were screened for S. aureus; 223 of those screened (24.5%) were positive and then decolonized with mupirocin. Among the 223 positive and decolonized patients, three (1.3%) developed a SSI. Among the 689 screen-negative patients, four (0.6%) developed SSIs for an overall rate of 0.77%. Among the 583 control patients who were not screened or decolonized, 10 (1.7%) developed S. aureus SSIs. SSIs from other organisms were 0.44% and 0.69%, respectively.

We 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 aureus is considered a source of subsequent infection in health care settings. Utilization of real-time polymerase chain reaction (PCR) for detection of S. aureus has 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. aureus colonization 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 femA gene. 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% versus 96%, 100% versus 100%, 100% versus 100%, and 98% versus 99%, respectively. In the adults the results were 90% versus 100%, 100% versus 98%, 100% versus 96%, and 95% versus 100%, respectively. Real-time PCR was able to detect S. aureus in 2 hours compared to 1 to 4 days for culture and provided sensitivity equal to or greater than culture.