Validation of a modified rapid test to detect the cefazolin inoculum effect in methicillin-susceptible <i>Staphylococcus aureus</i> from bloodstream infections in hospitals from North and Latin America
Bibliographic record
Abstract
BACKGROUND: The cefazolin inoculum effect (CzIE), defined here as a cefazolin MIC at high inoculum (107 colony-forming units/mL) ≥16 mg/L in MSSA, has been associated with less favourable clinical outcomes. However, detection of this phenotype is challenging in the clinical microbiology laboratory. We previously described modification of a rapid nitrocefin test using ampicillin disks rather than ampicillin powder for induction of the Staphylococcus aureus β-lactamase (BlaZ). OBJECTIVE: Evaluate the performance of the modified rapid nitrocefin test in a blinded fashion using MSSA isolates recovered from patients with bacteraemia. METHODS: We evaluated 200 MSSA isolates recovered from Latin American (LA) and North American (NA) hospitals (67 and 133 from NA and LA, respectively). The CzIE was determined using the modified rapid nitrocefin test with ampicillin disks and compared with MIC determination at high inoculum (gold standard). All isolates were subjected to whole-genome sequencing on an Illumina Hi-Seq platform. Performance metrics were calculated for the complete dataset and according to specific BlaZ types. RESULTS: The prevalence of the CzIE was 53% (105/200). Compared with the gold standard, the modified nitrocefin rapid test had a sensitivity of 96% and a specificity of 91.6%, with an overall accuracy of 94%. There were no false-positive results among blaZ-negative MSSA strains. CONCLUSIONS: The modified nitrocefin rapid test exhibited a robust performance to detect the CzIE in isolates from the Americas. This methodology is inexpensive and can be implemented in clinical microbiology laboratories around the world, including those with limited resources.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.006 | 0.010 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".