(88 days)
chromID® Strepto B agar is a selective chromogenic medium that is intended to aid in the qualitative determination of Group B Streptococcus (GBS) colonization in pregnant women. This medium supports the growth of, but does not differentiate between, hemolytic and non-hemolytic GBS strains. The test is performed on 18-24 hour LIM broth enrichments of vaginal/rectal swabs obtained from pregnant women. chromID® Strepto B agar results can be interpreted after 24 hours incubation with confirmation of characteristic GBS colonies from the media.
chromID® Strepto B agar is not intended to diagnose infection nor to guide or monitor treatment for infections. chromID® Strepto B agar does not provide susceptibility results. Subculture to non-selective media should be performed as needed for susceptibility testing. chromID® Strepto B agar is intended for use by laboratory health practitioners in a clinical laboratory.
chromID Strepto B agar consists of a nutritive base combining different peptones, chromogenic substrates and antibiotics. These components enable the screening of S. agalactiae by the spontaneous appearance of pale pink to red colonies. Most other bacterial species and yeasts do not grow on this medium or do not produce typical colonies.
Here's a breakdown of the acceptance criteria and the study that proves the device meets them, based on the provided text:
1. Table of Acceptance Criteria and Reported Device Performance:
| Performance Metric | Acceptance Criteria | Reported Device Performance (24 hours) |
|---|---|---|
| Sensitivity | Not explicitly stated in the document, but typically aims for high. | 97.7% (95% CI: 94.3% - 99.1%) |
| Specificity | Not explicitly stated in the document, but typically aims for high. | 92.1% (95% CI: 89.4% - 94.1%) |
| Analytical Reactivity | Detect GBS strains at low inoculum. | 12/20 at 18h, 17/20 at 24h, 20/20 at 48h (at 10 CFU/ml) |
| Analytical Specificity | Most non-GBS organisms should not grow or produce non-typical colonies. | 20/88 strains grew at 24h (3 with characteristic colonies); 30/88 grew at 48h (6 with characteristic colonies) |
| Mixed Infection (GBS recovery in presence of non-target) | GBS detected in presence of high levels of non-target organisms. | Both GBS strains detected at 24h in presence of 10^8 CFU/ml non-target (except for Streptococcus Group C); non-target organisms grew as non-characteristic colonies when diluted. |
| Incubation Time | Acceptable growth and characteristic colonies within specified timeframes. | 8/10 GBS strains showed characteristic colonies at 24 hours. |
| Recovery | Lowest CFU/ml detected. | 10^3 CFU/ml for both GBS strains. |
| Reproducibility | Expected results 100%. | 100% of 990 times tested. |
| Quality Control | 100% correct results for positive and negative controls. | 100% correct for 107 times tested. |
| Interfering Substances | No interference or limited inhibition. | No interference for most; partial inhibition from naproxen sodium and topical agent. |
Note: The document only provides the reported performance and implies that these values are acceptable as it concludes substantial equivalence. Explicit numerical acceptance criteria for sensitivity and specificity are not directly stated in the text.
2. Sample Size Used for the Test Set and Data Provenance:
- Sample Size: A total of 681 vaginal/rectal specimens enriched in LIM broth were analyzed during the clinical trial.
- Data Provenance: The data was collected from fresh clinical specimens at three external sites. This indicates that the data is prospective and originates from a clinical setting (likely within the USA, given the FDA filing).
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").
- It mentions that for the Reference Culture Method, "all suspicious colonies were screened to confirm or rule-out the presence of GBS using established laboratory methods: gram stain, catalase, PYR testing, and latex agglutination. VITEK® MS was also used to confirm the identification of GBS by the Reference Method." This implies that laboratory health practitioners (as stated in the intended use for the device) with relevant microbiology expertise were responsible for establishing the ground truth.
4. Adjudication Method for the Test Set:
- The document does not describe an explicit adjudication method (like 2+1 or 3+1).
- Instead, for the Reference Culture Method, it states that "all suspicious colonies were screened to confirm or rule-out the presence of GBS using established laboratory methods: gram stain, catalase, PYR testing, and latex agglutination. VITEK® MS was also used to confirm the identification of GBS by the Reference Method." This suggests a sequential confirmation process using multiple established laboratory tests to arrive at a confirmed ground truth, rather than an adjudication among independent readers.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was Done:
- No, an MRMC comparative effectiveness study was not done.
- This study evaluates a culture medium (chromID® Strepto B agar) against a "Reference Culture Method" for detecting Group B Streptococcus. It's a comparison of diagnostic methods, not human reader performance with and without AI assistance. Therefore, there is no effect size reported for human readers improving with AI.
6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) was Done:
- Yes, a standalone performance evaluation was done. The "device" in this context is the chromID® Strepto B agar medium.
- The clinical study directly compares the results obtained from the chromID® Strepto B agar (interpreting characteristic colonies after 24 hours, followed by confirmation) to a "Reference Culture Method." The reported sensitivity and specificity values represent the standalone performance of the chromID® Strepto B agar in identifying GBS from clinical specimens.
- It's important to note that the device's intended use specifies "chromID® Strepto B agar results can be interpreted after 24 hours incubation with confirmation of characteristic GBS colonies from the media," indicating that a human laboratory health practitioner is always in the loop for confirmation, but the primary sensitivity and specificity reported directly reflect the medium's ability to selectively grow and display characteristic GBS colonies.
7. The Type of Ground Truth Used:
- The ground truth used was expert consensus / established laboratory methods for microbiology.
- The "Reference Culture Method" served as the gold standard, involving:
- Subculture to CNA agar.
- Screening suspicious colonies with gram stain, catalase, PYR testing, and latex agglutination.
- Confirmation with VITEK® MS.
8. The Sample Size for the Training Set:
- The document does not explicitly mention a "training set" for the chromID® Strepto B agar. This is typical for traditional in-vitro diagnostic devices like culture media, which are developed and validated through analytical studies and then assessed in clinical studies, rather than "trained" like AI algorithms.
- The design and formulation of the medium come from developmental work, but there isn't a "training set" in the machine learning sense.
9. How the Ground Truth for the Training Set Was Established:
- As there is no explicit "training set" mentioned in the context of an algorithm, the concept of establishing ground truth for a training set is not directly applicable to this device description. The performance is assessed against established laboratory practices and known bacterial strains for analytical studies.
§ 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.