Rapid MRSA screening tests can have an impact both at the individual and group level because they can improve patient outcomes by permitting early detection of MRSA carriage and rapid contact isolation. The principal findings of this study evaluating a rapid MRSA test in critically ill patients are as follows. ICU admission prevalence of previously unknown MRSA carriers was high. Only a small minority of patients had their first MRSA isolate from a routine clinical culture. The qMRSA test decreased overall time to notification from four days to one day and helped to identify previously unknown MRSA carriage rapidly. No effect on MRSA infection rates was observed in the surgical ICU, although a large number of unnecessary pre-emptive isolation days could be saved in this unit by using the qMRSA test. Finally, a substantial decrease in MRSA infections was seen in the medical ICU after increasing compliance with on-admission screening and linking the rapid test to pre-emptive isolation and cohorting of MRSA patients.
Despite the fact that culture-based MRSA screening techniques have proven cheap and sensitive if samples are collected from several body sites, the time to report the results remains a major issue. Definitive identification and testing results are usually available only 48 to 96 hours after sample collection, a time delay that could allow MRSA cross-transmission if patients are not presumptively placed under contact precautions [19
]. This may be one of the reasons (apart from low hand hygiene compliance) why the recently published study by Cepeda and colleagues [4
] did not identify a significant effect of contact isolation for MRSA carriers identified by conventional methods [29
This study is the first to report detailed time intervals from patient admission to notification of MRSA test results in critically ill patients. Previous reports on rapid MRSA screening tests only assessed the time of specimen processing, without taking into account transport of specimens and the delay between admission and screening [18
]. Our findings show that factors other than laboratory analysis may have an effect on total time from admission to notification of test results, and that efforts are warranted to reduce these delays. The added value of providing molecular screening capability during nights and weekends remains to be assessed.
The few investigations that specifically evaluated the prevalence of MRSA carriage on ICU admission differ from ours in important ways, and so comparisons are limited. However, our study confirms that the prevalence of previously unknown MRSA carriage at admission to critical care is high in settings with endemic MRSA transmission. Previously reported prevalences of MRSA carriage at ICU admission ranged between 6% and 34% [4
]. In all of these studies, fewer than 50% of MRSA carriers had previously been identified as such, emphasizing the importance of early screening to detect the unknown reservoir of MRSA patients.
Current limitations to routine implementation of PCR-based MRSA screening tests are their high costs, the workload of specimen processing and the lack of trained laboratory technicians. We do not yet have sufficient data to demonstrate the cost-effectiveness of our rapid screening strategy. It is possible that MRSA control in the ICU setting may also be achieved with fewer resources and without rapid screening tools [11
]. Nevertheless, the rapid qMRSA test saved a large number of unnecessary isolation days in the surgical ICU and helped to decrease substantially MRSA infections in the medical ICU, making it likely that this intervention saved costs for the hospital. In addition, by saving unnecessary isolation days, we might have increased patient safety because isolation precautions may decrease provider–patient interactions and increase the rate of adverse events [37
In a recently reported mathematical model it was suggested that a policy of screening newly admitted patients for MRSA coupled with rapid contact isolation could reduce nosocomial MRSA infection [38
]. However, despite systematic on-admission screening and pre-emptive contact isolation, the incidence of MRSA infections did not decrease in the surgical ICU. By contrast, the medical ICU had greater success with MRSA control. This contradictory finding may reflect differences in case mix, frequency of patient movements outside the ICU, or compliance with standard precautions and isolation practices [39
]. Antibiotic selection pressure is rather low in the surgical ICU, making it unlikely that this factor confounded the study results [40
Our study has limitations. First, we used a rapid MRSA test that lacks perfect specificity and sensitivity. Therefore, we cannot exclude the possibility that the test artificially increased the number of isolation days needed due to false-positive qMRSA test results. Moreover, there may have been patients with false-negative screening results, in whom MRSA acquisition was erroneously attributed to the ICU. Second, we did not perform discharge screening during the entire study period, making it impossible to compare MRSA acquisition rates during the different study phases. Third, although colonization pressure was appropriately adjusted for, other potential confounding factors (such as antibiotic use, compliance with hand hygiene practices and isolation precautions, case-mix, or staffing levels) were not adjusted for in the analysis. Because these factors have been shown to fluctuate over time in a seasonal manner, the baseline ten-month period may have represented a biased estimate of year-round MRSA infection rates. Therefore, the data analysis provided offers only preliminary evidence regarding the effectiveness of the intervention.