1. Some studies have shown contradictory results about the effectiveness of MRSA screening. Why is that?

Several factors contribute to the effectiveness of MRSA surveillance. Notably, the testing methodology selected (e.g., PCR vs. culture) can affect not only test performance (sensitivity and specificity) but also turnaround time (TAT), which in turn can impact time to intervention (TTI). A study using a less sensitive method associated with false negatives and thus missed opportunities to isolate colonized patients could likely result in a lower reduction in MRSA infection. Similarly, if test results are not acted on within 24 hours, colonized patients may not be isolated in time to avoid transmission to other patients.

2. What is the difference between time to intervention (TTI) and turnaround time (TAT)?

Time to intervention (TTI) focuses on colonized patients (i.e., those who test positive for MRSA during screening). TTI is the time elapsed from admission and collection of the patient sample to the time when the colonized patient is isolated. In addition to TAT, which is a contributing factor, TTI depends on clinical workflow (e.g., when and how test results are accessed and reviewed by clinicians, logistics of isolating patients) and hospital infrastructure.

3. Why is TTI important?

Published data suggest that a time to intervention of ≤24 hours is necessary for MRSA reduction. A delay in time to intervention can be costly in two ways. Delayed isolation of patients who test positive can result in increased risk of spreading the disease. Or, in hospitals that preemptively isolate high-risk patients, this could result in unnecessary isolation, which is costly. Thus, experts point to a reporting time of ≤15 hours as optimal for identifying and isolating colonized patients.1,3,4

4. What is the definition of “captured isolation days”?

“Captured isolation days” is a measure of the success with which a facility is able to identify and, just as importantly, isolate colonized patients. It is defined as “days during which a patient colonized or infected with MRSA [is] placed in isolation.” The captured isolation days are measured against the patient’s length of stay (captured isolation days divided by length of stay). Captured isolation days has been shown to be a predictor of the success of a surveillance program, with captured isolation days of 80% or greater being associated with success.

5. If timing is important, then wouldn’t a stat test, which provides results within 2 hours, be preferable?

For disease diagnosis, fast TAT is often desirable. For screening, as is the case with MRSA surveillance, the economics of batch testing, combined with the fact that most hospital infrastructures cannot support patient intervention on a stat basis, makes it difficult to justify stat testing.

6. What about the cost of culture vs. PCR? How do we justify the incremental cost of going to PCR?

While culture media and reagents cost less than PCR reagents, PCR methods, such as the Roche LightCycler® MRSA Advanced Test, are less labor intensive. Furthermore, PCR is a more sensitive method, so it may identify more colonized patients who require isolation; this ultimately could result in fewer infections and lower cost of care.

7. Our hospital uses a culture method for MRSA surveillance currently. Is there a way we can model the likely impact of switching over to a PCR method?

The Budget Impact Model (BIM) has been developed to help hospitals and labs look at different scenarios and forecast the likely outcome (e.g., reduction in MRSA infection) and the associated cost impact of each scenario.

8. How was the BIM developed?

The BIM was developed through a two-year process incorporating comprehensive literature review, interviews with key stakeholders (clinicians, microbiologists, infection control practitioners, hospital administrators and payers) and input from health economists and other specialists. A description of the model was published in a peer-reviewed journal.3

9. How can I access the BIM?

To assess the potential value of MRSA surveillance for you and your institution, please contact your Roche representative.


  1. Robicsek A, Beaumont JL, Paule SM, et al. Ann Intern Med 2008;148:409-418.
  2. Olchanski N, Mathews C, Fusfeld L, Jarvis W. Infect Control Hosp Epidemiol 2011;32:250-257.
  3. Peterson LR, Diekema DJ. J Clin Microbiol 2010;48:683-689.
  4. Peterson LR, Karchmer T, Tenover FC. N Engl J Med 2011;365:761-762.