(90 days)
Granada Medium is a selective and differential agar which is intended for the qualitative detection of Group B Streptococus (GBS) from LIM Broth enrichment cultures of vaginal/rectal swabs from antepartum women following 18-24 hours of incubation.
Recovery of orange colored colonies on Granada Medium is a positive result for presence of β-hemolytic GBS. Results can be interpreted after 18-24 hours of anaerobic incubation. Due to the properties of Granada Medium, white colonies recovered on Granada Medium must undergo additional testing to confirm absence of GBS colonies must be performed for conducting susceptibility testing as recommended for penicillin- allergic women. A lack of growth or the absence of orange colonies on Granada Medium does not presence of GBS. Granada Medium is not intended to diagnose infection, or to guide or monitor treatment for infections.
Hardy Diagnostics Granada Medium agar utilizes the Granada reaction and contains the necessary components for pigment detection of beta-hemolytic GBS. The production of a light orange to dark orange pigmented colony is a unique characteristic of hemolytic GBS on Granada Medium due to a reaction with substrates such as starch, peptone, serum, and folate pathway inhibitors.
Here's a breakdown of the acceptance criteria and study details for the Granada Medium device:
1. Table of Acceptance Criteria and Reported Device Performance
The acceptance criteria are not explicitly stated as numerical targets in the provided document, but rather implied by the overall performance comparison to the reference method and the conclusion of substantial equivalence. The key performance metrics reported are sensitivity and specificity for GBS detection.
| Performance Metric | Acceptance Criteria (Implied) | Reported Device Performance (Overall) |
|---|---|---|
| Sensitivity (GBS, Table 1) | High, comparable to reference method for detecting GBS (β-hemolytic and non-hemolytic) | 94.5% (95% CI: 89.8 - 97.1) |
| Specificity (GBS, Table 1) | High, comparable to reference method for detecting GBS (β-hemolytic and non-hemolytic) | 98.0% (95% CI: 96.6 - 98.9) |
| Sensitivity (β-hemolytic GBS, Table 2) | High, comparable to reference method for detecting β-hemolytic GBS | 98.1% (95% CI: 94.5 - 99.3) |
| Specificity (β-hemolytic GBS, Table 2) | High, comparable to reference method for detecting β-hemolytic GBS | 97.9% (95% CI: 96.4 - 98.8) |
| Recovery Rate (LoD) for S. agalactiae ATCC® 12386 & ATCC® 12403 (direct inoculation) | Low concentration for positive reaction | 1.5x10² CFU/mL (15 CFU) |
| Recovery Rate (LoD) for S. agalactiae ATCC® 12386 & ATCC® 12403 (after LIM Broth enrichment) | Low concentration for positive reaction after enrichment | 1.5x10² CFU/mL (4.5 CFU) |
| Analytical Reactivity (GBS Strains) | All tested GBS strains produce expected color at LoD | 100% of 54 GBS strains (48 β-hemolytic, 6 non-hemolytic) produced expected color reaction |
| Analytical Specificity (Non-target Organisms) | Negative color reaction or no recovery | 100% (39/84 negative color, 45/84 no recovery) |
| Microbial Interference | Recovery of target GBS in presence of high concentrations of non-target organisms | Expected orange color and recovery for all but one non-target organism; E. faecalis (ATCC 29212) inhibited at high concentration, but GBS recovered when E. faecalis concentration reduced |
| Interference (Exogenous/Endogenous) | No interference with growth or color reaction | No interference observed for any tested substance at highest clinically relevant concentration |
| Incubation Time | All organisms grow with visible orange colonies within the range | All organisms grew with visible orange colonies by 18 hours (set range 18-24 hours) |
| Specimen Stability | Recovery of GBS for all time points and storage conditions | 100% recovery from specified swabs at room temp (up to 24 hours) and 2-8°C (up to 120 hours) |
| Reproducibility | >95% agreement with known test results | >95% agreement; 100% of β-hemolytic GBS isolates recovered with expected orange color |
2. Sample Size Used for the Test Set and Data Provenance
- Sample Size (Clinical Study): A total of 771 valid clinical specimens were tested (out of 884 initially collected, with 113 excluded for not meeting enrollment criteria).
- Data Provenance: The study was conducted at four geographically diverse hospitals with routine GBS specimens in the form of vaginal/rectal swabs. This suggests a multi-center, potentially prospective (implied by "routine GBS specimen") collection of real-world clinical samples. It does not explicitly state the country of origin, but "US Food & Drug Administration" context usually refers to studies conducted in the USA or accepted for the US market. The nature of the study (comparing to a reference method) indicates it's a diagnostic accuracy study.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts
The document does not specify the number of experts or their qualifications for establishing the ground truth. It describes the "reference method" as:
- Selective enrichment of specimen in LIM Broth
- Followed by subculture to blood agar
- Confirmation of Group B Streptococci by: hemolytic reaction on blood agar, gram-stain, catalase test, and StrepPRO™ latex agglutination.
This indicates a standard microbiology laboratory workflow, where trained laboratory personnel (e.g., medical technologists, microbiologists) would be performing and interpreting these established diagnostic tests. The discrepant analysis involved isolates being returned to Hardy Diagnostics for re-testing and confirmation of identity, implying expertise at the manufacturer's facility as well.
4. Adjudication Method for the Test Set
The document primarily describes a comparison against a "reference method" and subsequent "discrepant analysis."
- For the initial comparison (Table 1 and 2), the "reference method" was considered the ground truth.
- For Discrepant Analysis: All discrepant isolates (False Positives and False Negatives) were re-tested and confirmed using the reference method described above (hemolytic reaction, gram-stain, catalase, StrepPRO™ latex agglutination). This serves as an adjudication method where initial discrepancies are resolved by re-examination using definitive laboratory tests.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
- No, an MRMC comparative effectiveness study was not explicitly described in the provided text. The study focuses on the standalone performance of the Granada Medium compared to a traditional reference laboratory method.
- A brief mention under Reproducibility states: "The testing was done with at least one operator and two readers, blinded to each other's results, per site." This element incorporated some "multi-reader" aspects for reproducibility checks but this was for concordance of interpretations of Granada Medium itself, not a comparative effectiveness study of human readers with vs. without AI assistance. The device is a culture medium, not an AI-assisted diagnostic tool for interpretation.
6. Standalone (Algorithm Only Without Human-in-the-Loop Performance) Study
- Yes, a standalone study was performed. The clinical performance data (Tables 1 and 2) directly compares the results of the Granada Medium (interpreted visually for orange colonies, which is a human interpretation step, but without assistance from another diagnostic tool) against the established laboratory reference method. The device's "performance" is its ability to produce a visual indicator (orange colonies) corresponding to GBS presence. This is its "standalone" performance in its intended use. There is no AI algorithm involved.
7. The Type of Ground Truth Used
The ground truth used was expert consensus / established laboratory methods which identified specific bacterial species. Specifically:
- The "reference method" involved selective enrichment in LIM Broth, subculture to blood agar, and confirmation based on hemolytic reaction, gram-stain, catalase test, and StrepPRO™ latex agglutination. This is a highly accurate and accepted method for identifying Group B Streptococci in clinical microbiology.
- For analytical studies (reactivity, specificity, LoD), well-characterized ATCC, NCIMB, NCTC reference strains and clinical GBS isolates were used, which represent a known ground truth.
8. The Sample Size for the Training Set
- The document does not explicitly mention a separate "training set" as would be typical for machine learning or AI models.
- For a diagnostic device like a culture medium, the development and initial optimization (which parallels a "training" phase) would typically involve internal laboratory testing with known bacterial strains and challenging conditions. While not quantified as a "training set" in the context of this document, the Analytical Reactivity, Specificity, Recovery Rate, Microbial Interference, and Incubation studies collectively represent the robust characterization and "training" of the medium's performance during development. These studies involved specific numbers of ATCC/reference strains and non-target organisms (e.g., 54 GBS strains for reactivity, 84 non-target organisms for specificity).
9. How the Ground Truth for the Training Set Was Established
Given that a specific "training set" with separate ground truth establishment wasn't explicitly defined for an AI model, for the developmental and analytical studies (which function similarly to training data for the medium's design):
- The ground truth was established by using well-characterized, identified bacterial strains (ATCC, NCIMB, NCTC reference strains, and clinical isolates).
- For these strains, their identity (e.g., S. agalactiae, specific serotypes, or other bacterial species) was already established through standard microbiological identification techniques.
- The "expected color development" (orange for β-hemolytic GBS, white for non-hemolytic GBS, negative for non-GBS organisms) served as the pre-defined target for the medium's differentiation capabilities, based on the known Granada reaction.
§ 866.2360 Selective culture medium.
(a)
Identification. A selective culture medium is a device that consists primarily of liquid or solid biological materials intended for medical purposes to cultivate and identify certain pathogenic microorganisms. The device contains one or more components that suppress the growth of certain microorganisms while either promoting or not affecting the growth of other microorganisms. The device aids in the diagnosis of disease caused by pathogenic microorganisms and also provides epidemiological information on these diseases.(b)
Classification. Class I (general controls). The device is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 866.9.