Interpretation of MRSA <i>Select</i> Screening Agar at 24 Hours of Incubation
Bibliographic record
Abstract
An incubation time of 24 h at 35 to 38 degrees C is recommended for the optimal performance of MRSASelect (Bio-Rad) chromogenic screening agar. An additional 24 h is required to capture slow-growing methicillin-resistant Staphylococcus aureus (MRSA). However, the normal hours of operation for most laboratories cannot reliably accommodate 24-h interpretation intervals. Daily agar plate interpretations are more likely to occur around 18 h and 42 h of incubation, which may compromise the performance of the chromogenic agar and negatively impact patient infection control efforts. In order to validate the importance of stringent incubation times to plate performance, we evaluated MRSASelect medium at controlled intervals of 24 and 48 h of incubation, using clinical MRSA-screening swabs. A total of 1,071 MRSA-positive and 2,733 MRSA-negative cultures were selected for analysis. Compared to 48-h-incubation results, the sensitivity and specificity of MRSASelect at 24 h were 98.3% and 98.2%, respectively. Only 19 of 1,071 (1.8%) MRSA-positive isolates required 48 h for detection. Holding 24-h negative plates an additional 24 h resulted in the workup of 253 (6.6%) pink, yet non-MRSA, colonies. The 24-h positive and negative predictive values of MRSASelect, assuming MRSA prevalences of 1, 5, and 10%, were 35.5 and 99.98%, 74.2 and 99.9%, and 85.9 and 99.8%, respectively. MRSASelect medium held for 24-h incubation is a highly sensitive and specific MRSA-screening tool. Further incubation prolongs the turnaround time for results and creates a significant amount of unnecessary work in the laboratory.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".