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Strep B Carrot Broth™ One-Step is a selective and differential medium which is intended for the detection of Group B Streptococcus (GBS) from anovaginal specimen collected from pregnant women. The medium is used as an aid in the qualitative determination of GBS colonization in pregnant women. The color change reaction from white to orange is representative of a positive result for presence of GBS. The medium requires 24 hours of incubation but positive results can be interpreted as early as 16 hours. Due to the properties of Strep B Carrot Broth™ One-Step, non-hemolytic GBS cannot be detected by the medium's color change and require subculture for identification. Any presumptive negative indicated by lack of color change at the incubation period must be subcultured to a non-selective medium (e.g. Tryptic Soy Agar with 5% Sheep Blood) to confirm absence of GBS. Subculture must also be performed to recover isolates for conducting susceptibility testing as recommended for penicillin-allergic women.

Strep B Carrot Broth™ One-Step is a selective and differential medium with selective components designed to enrich for Group B Streptococci. The production of a light orange, or red-orange pigment is a unique characteristic of hemolytic GBS due to reaction with substrates such as starch, peptone, serum, and folate pathway inhibitors. GBS detection with Strep B Carrot Broth™ One-Step is only possible with β-hemolytic Group B Streptococci colonies, providing evidence of a direct genetic linkage between pigment production in this media and hemolysin production. Non-hemolytic GBS can be recovered from Strep B Carrot Broth™ One-Step upon subculture to 5% sheep blood agar plates.

The provided text describes the performance evaluation of the "Strep B Carrot Broth™ One-Step" device. Here's a breakdown of the requested information:

1. Table of Acceptance Criteria and Reported Device Performance

The document doesn't explicitly state "acceptance criteria" in a separate section with numerical targets. However, the performance data presented (sensitivity and specificity) is implicitly the criteria the device met for substantial equivalence. The predicate device's performance is not provided in numerical values, but the comparison is implied through the overall "Substantially Equivalent?" column.

2. Sample Size Used for the Test Set and Data Provenance

• Test Set Sample Size: A total of 884 specimens were initially collected, but 113 were excluded, resulting in 771 valid samples for the primary comparison.
  • Data Provenance: The study was conducted at four geographically diverse hospitals with routine GBS specimens (anovaginal swabs). This indicates a prospective collection within normal clinical practice. The country of origin is not explicitly stated but implied to be the US given the FDA submission.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications

• The document does not explicitly state the number of experts or their specific qualifications (e.g., "radiologist with 10 years of experience") for establishing ground truth.
• Ground Truth Establishment: For the primary comparison, the reference method was "routine culture," defined as:
  • Selective enrichment in LIM Broth.
  • Followed by subculture to Blood Agar.
  • Confirmed by biochemical testing.
  • Organisms grown on Blood Agar were confirmed using gram-stain, catalase test, and latex agglutination.
  • Discrepant isolates underwent re-testing and confirmation at Hardy Diagnostics using a "discrepant analysis protocol." This re-testing included confirming identity (β-hemolytic GBS, non-hemolytic GBS, or non-GBS) and testing at the Limit of Detection (LoD).

4. Adjudication Method for the Test Set

• The document implies a form of adjudication for discrepant results. All discrepant isolates (false positives and false negatives) were re-tested and confirmed at Hardy Diagnostics using a specific "discrepant analysis protocol." This suggests a process where initial disagreements between the test device and the reference method were further investigated to establish the definitive ground truth. It is not explicitly described as a 2+1 or 3+1 method; rather, it appears to be a single "expert site" (Hardy Diagnostics) reviewing discrepancies.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done

• No, an MRMC comparative effectiveness study was not explicitly done as described. The study evaluates a culture medium, not an imaging AI diagnostic device. The "reproducibility" section mentions "at least one operator and two readers, blinded to each other's results, per site" for the reproducibility panel of 12 isolates, but this is to demonstrate proficiency and reproducibility of the device itself, not to compare human reader performance with and without AI assistance on a large test set. Therefore, no effect size of human readers improving with AI vs. without AI assistance is reported.

6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done

• Yes, a standalone performance was done for the "Strep B Carrot Broth™ One-Step" in its primary mode of operation. The device is a culture medium designed to produce a visual color change. The performance metrics (sensitivity and specificity in Table 1) directly reflect the device's ability to produce this color change as a standalone indicator of GBS presence, compared to the reference method. The subsequent subculture for negatives or non-hemolytic GBS is part of the overall diagnostic workflow, but the initial "color reaction" is a standalone readout.

7. The Type of Ground Truth Used

• The ground truth used was expert consensus informed by a reference culture method (LIM Broth + subculture to Blood Agar) and confirmed by biochemical testing, gram-stain, catalase test, and latex agglutination. For discrepant cases, further re-testing and confirmation at a central lab (Hardy Diagnostics) was performed. This is a form of laboratory reference standard.

8. The Sample Size for the Training Set

• The document does not mention a training set sample size. This is common for traditional culture media, which are developed based on established microbiological principles and validated rather than "trained" in the machine learning sense. The performance data presented is for validation.

9. How the Ground Truth for the Training Set Was Established

• As there is no explicit mention of a training set, the method for establishing ground truth for a training set is not applicable or provided.

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