P-2083. Validation of the Modified Rapid Test for detection of the Cefazolin Inoculum Effect (CzIE) in bloodstream isolates of Methicillin-<i>Susceptible Staphylococcus aureus</i> (MSSA) from North and Latin America
Bibliographic record
Abstract
Abstract Background S. aureus is a major human pathogen and a leading cause of bloodstream infections (BSI). Cefazolin is frequently used for severe deep-seated MSSA infections, as in general it displays similar efficacy and a more favorable side effect profile as compared to isoxazolyl-penicillins. In some studies, the CzIE has been associated with therapeutic failures and mortality in MSSA BSI treated with cefazolin, however, current laboratory testing methods are unable to detect the CzIE. The aim of this study was to conduct a blinded evaluation of a modified colorimetric rapid test to detect the CzIE in MSSA isolated from BSI in North and Latin-America. Methods 99 MSSA recovered from BSI in North America (2019; n=69) and Latin-America (2011-2019; n=30), and previously characterized for the presence of the CzIE (71 CzIE + and 28 CzIE -) using gold-standard broth microdilution at high inoculum (breakpoint >= 16 ug/mL) were included. In a central laboratory in Colombia, a modified rapid colorimetric test (rCT) was performed according to a published protocol with modification that included the use of ampicillin (AMP) discs placed in 1 mL of BHI-broth for induction of β-lactamase expression. The researchers were blinded to the results of the gold standard test to detect CzIE. Diagnostic performance metrics were calculated and typing of BlaZ was performed using whole genome sequence data. Results Compared to the gold standard, the modified test showed a sensitivity and specificity of 97% and 86%, respectively, and overall accuracy of 94%. The predominant BlaZ β-lactamase types in the 99 MSSA were type C (70%) and type A (27%). When analyzing the performance of the rCT by BlaZ type, in isolates with type C enzyme the modified rapid test had a sensitivity of 96% and specificity of 82% with an accuracy of 91%. In isolates with BlaZ type A, the sensitivity and specificity of the rCT were 100%. Conclusion The modified rapid colorimetric test detected the CzIE in bloodstream MSSA from different geographic areas with a global accuracy of 94%. Notably, the accuracy of the test for BlaZ type A isolates was 100% and for BlaZ type C isolates was 91%. Further, the use of AMP discs proved to be a practical, time-saving modification that did not impair accuracy of the test. Disclosures William R. Miller, M.D., Merck: Grant/Research Support|UptoDate: Royalties
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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 | 0.003 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".