Cepheid Xpert MRSA Cycle Threshold in Discordant Colonization Results and as a Quantitative Measure of Nasal Colonization Burden

Stenehjem, Edward; Rimland, David; Crispell, Emily K.; Stafford, Cortney; Gaynes, Robert P.; Satola, Sarah W.

doi:10.1128/jcm.06690-11

Cited by 13 publications

(12 citation statements)

References 19 publications

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“…The mean C T value of the false-positive (culture-negative and PCR-positive) samples was significantly higher than that of concordant samples (31.0 vs. 24.6). These findings are in line with the previous studies showing that the discrepancies between the Xpert MRSA assay and culture method occurred exclusively when the bacterial density was low [9] and agree with the fact that the C T value in the Xpert MRSA assay correlates strongly with the bacterial density in the samples [9, 14]. The discordance from the five false-negative results might be partially explained by the cases with low bacterial density of MRSA in the nostrils or disparity in the specimens from two nostrils (Table 2).…”

Section: Discussionsupporting

confidence: 92%

Comparative Evaluation of Three Chromogenic Media Combined with Broth Enrichment and the Real-Time PCR-Based Xpert MRSA Assay for Screening of Methicillin- Resistant Staphylococcus aureus in Nasal Swabs

Lee

Park

et al. 2013

Ann Lab Med

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BackgroundWe evaluated the performance of three chromogenic media (Brilliance agar I [Oxoid, UK], Brilliance agar II [Oxoid], and ChromID MRSA [Biomérieux, France]) combined with broth enrichment and the Xpert MRSA assay for screening of methicillin-resistant Staphylococcus aureus (MRSA).MethodsWe obtained 401 pairs of duplicate nasal swabs from 321 patients. One swab was suspended overnight in tryptic soy broth; 50-µL aliquots of suspension were inoculated on the three chromogenic media. Brilliance agar I and II were examined after 24 hr, and ChromID MRSA, after 24 and 48 hr. The paired swab was processed directly using real-time PCR-based Xpert MRSA assay.ResultsTrue positives, designated as MRSA growth in any of the culture media, were detected with the prevalence of 17% in our institution. We report the sensitivity, specificity, positive predictive value, and negative predictive value of MRSA growth as follows: 92.3%, 94.0%, 75.9%, and 98.4% in Brilliance agar I (24 hr); 92.7%, 97.9%, 90.0%, and 98.5% in Brilliance agar II (24 hr); 95.6%, 95.8%, 82.3%, and 99.1% in ChromID MRSA (24 hr); 100%, 92.5%, 73.1%, and 100% in ChromID MRSA (48 hr); 92.6%, 96.7%, 85.1%, and 98.5% in Xpert MRSA assay. The agreement between the enriched culture and Xpert MRSA assay was 96.0%.ConclusionsThree chromogenic culture media combined with enrichment and Xpert MRSA assay demonstrated similar capabilities in MRSA detection. The Xpert MRSA assay yielded results comparable to those of culture methods, saving 48-72 hr, thus facilitating earlier detection of MRSA in healthcare settings.

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Section: Discussionsupporting

confidence: 92%

Comparative Evaluation of Three Chromogenic Media Combined with Broth Enrichment and the Real-Time PCR-Based Xpert MRSA Assay for Screening of Methicillin- Resistant Staphylococcus aureus in Nasal Swabs

Lee

Park

et al. 2013

Ann Lab Med

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“…In agreement with a prior report, we found a negative correlation between the C T value and the number of MRSA colonies in the nares. 27 We found a poor correlation between the C T value from the study’s nasal swabs and the nasal swabs collected by the hospital nurses. We believe this poor correlation reflects a wide variability in collection techniques.…”

Section: Discussionmentioning

confidence: 69%

Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Real-Time PCR: A Predictive Tool for Contamination of the Hospital Environment

Livorsi

Arif

Garry

et al. 2015

Infect. Control Hosp. Epidemiol.

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Introduction We sought to determine whether the bacterial burden in the nares, as determined by the cycle threshold (CT) value from real-time MRSA PCR, is predictive of environmental contamination with MRSA. Methods Patients identified as MRSA nasal carriers per hospital protocol were enrolled within 72 hours of room admission. Patients were excluded if 1) nasal mupirocin or chlorhexidine body-wash was used within the past month or 2) an active MRSA infection was suspected. Four environmental sites, 6 body sites and a wound, if present, were cultured with pre-moistened swabs. All nasal swabs were submitted for both a quantitative culture and real-time PCR (Roche Lightcycler, Indianapolis, IN). Results 82 patients had a positive MRSA-PCR at study enrollment. There was a negative correlation of moderate strength between the CT value and the number of MRSA colonies in the nares (r= −0.61, p<0.01). Current antibiotic use was associated with lower levels of MRSA nasal colonization (CT value: 30.2 vs. 27.7, p<0.01). Patients who had concomitant environmental contamination had higher median log MRSA nares count (3.9 vs. 2.5, p=0.01) and lower CT values (28.0 vs. 30.2, p<0.01). However, a ROC curve was unable to identify a threshold MRSA nares count that reliably excluded environmental contamination. Conclusions Patients with a higher burden of MRSA in their nares, based on the CT value, were more likely to contaminate their environment with MRSA. However, contamination of the environment cannot be predicted solely by the degree of MRSA nasal colonization.

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“…The capacity of this test to quantify organisms has been also reported by Stenehjem et al, who determined nasal colonization bioburdens in swabs using the Xpert MRSA test [26]. The most obvious benefit of this test is that it provides information on which to base the choice of antibiotic treatment for patients with suspected pneumonia in less than an hour after the sample arrives at the laboratory.…”

Section: Resultsmentioning

confidence: 79%

Evaluation of the Xpert Carba-R (Cepheid) Assay Using Contrived Bronchial Specimens from Patients with Suspicion of Ventilator-Associated Pneumonia for the Detection of Prevalent Carbapenemases

et al. 2016

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There is a critical need for rapid diagnostic methods for multidrug-resistant (MDR) pathogens in patients with a suspicion of ventilator-associated pneumonia (VAP). The Xpert Carba-R detects 5 targets for carbapenemase-producing organisms (blaKPC, blaNDM, blaVIM, blaOXA-48, and blaIMP-1). Our objective was to evaluate the performance of this assay directly on bronchial aspirates and to correlate the cycle number for a positive result (Ct) with the bacterial count. Bronchial aspirates from patients with a suspicion of VAP were spiked with a dilution of 1 of 4 MDR organisms carrying the resistance genes detected by the test prepared to a final concentration of 102−105 cfu/mL. We used a ROC curve and provided areas under the curve (AUC) with their 95% confidence intervals (CI). A point of maximum sensitivity (Se) and specificity (Sp) was derived and validity indices were calculated. One hundred contrived tests were performed. Se and Sp were 100% for all bacterial counts. A positive sample with a Ct ≤24.7 corresponded to a count ≥105 cfu/mL; if the Ct was within the range >24.7-≤26.9, this corresponded to a count ≥104 cfu/mL. When the Ct was >26.9, this corresponded to a count <104 cfu/mL. The Xpert Carba-R detects carbapenemase-producing organisms directly in contrived bronchial aspirates. Still, an important issue to consider is that the number of gene copies may vary according to many factors in vivo. If confirmed in further studies, the strong correlation observed between Ct values and the results of semiquantitative cultures suggests this test could serve to differentiate between infection and colonization in routine clinical practice.

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Cepheid Xpert MRSA Cycle Threshold in Discordant Colonization Results and as a Quantitative Measure of Nasal Colonization Burden

Cited by 13 publications

References 19 publications

Comparative Evaluation of Three Chromogenic Media Combined with Broth Enrichment and the Real-Time PCR-Based Xpert MRSA Assay for Screening of Methicillin- Resistant Staphylococcus aureus in Nasal Swabs

Comparative Evaluation of Three Chromogenic Media Combined with Broth Enrichment and the Real-Time PCR-Based Xpert MRSA Assay for Screening of Methicillin- Resistant Staphylococcus aureus in Nasal Swabs

Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Real-Time PCR: A Predictive Tool for Contamination of the Hospital Environment

Evaluation of the Xpert Carba-R (Cepheid) Assay Using Contrived Bronchial Specimens from Patients with Suspicion of Ventilator-Associated Pneumonia for the Detection of Prevalent Carbapenemases

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