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ETEST® is a manual, quantitative technique for the determination of antimicrobial susceptibility of non-fastidious Gram-negative and Gram-positive aerobic bacteria. The system comprises a predefined antibiotic gradient which is used to determine the Minimum Inhibitory Concentration (MIC, in ug/mL) of different antimicrobial agents against microorganisms tested on agar media after overnight incubation.

Fosfomycin has been shown to be active against the Gram-positive aerobic microorganisms listed below according to the FDA label for this antimicrobial agent.

ETEST® (FO) can be used to determine the MIC of Fosfomycin against the following microorganisms:

Active both in vitro and in clinical infections:

• Escherichia coli
• Enterococcus faecalis

ETEST® is a thin, inert and non-porous plastic strip carrying the MIC reading scale in µg/mL on one side and a predefined antibiotic gradient on the other side.

When the strip is applied to an inoculated agar surface, the preformed antibiotic gradient immediately transfers into the agar matrix, then forming a stable, continuous and exponential gradient of antibiotic concentrations directly underneath the strip. Bacterial growth becomes visible during incubation, and a symmetrical inhibition ellipse centered along the strip appears. The MIC value is read from the scale in terms of ug/mL at complete inhibition of bacterial growth, where the pointed end of the ellipse intersects the strip.

ETEST® Fosfomycin contains a range of fosfomycin from 0.032 to 512 ug/mL.

The provided document is a 510(k) premarket notification for a medical device called ETEST® Fosfomycin (FO) (0.032-512 ug/mL). This device is an Antimicrobial Susceptibility Test Powder used to determine the Minimum Inhibitory Concentration (MIC) of fosfomycin against certain bacteria.

Here's an analysis of the acceptance criteria and the study proving the device meets those criteria, based only on the provided text. Please note that the document is a regulatory submission, not a detailed scientific paper, so some requested information may not be explicitly stated or might not be applicable to this type of device (e.g., "human readers" for an in-vitro diagnostic).

1. A table of acceptance criteria and the reported device performance

The acceptance criteria for this type of device are generally qualitative (e.g., "acceptable performance," "substantially equivalent," "meets guidance document performance requirements") and quantitative, primarily focusing on "Essential Agreement" and "Category Agreement" with a reference method. The document states that ETEST® Fosfomycin (FO) "demonstrated substantially equivalent performance when compared with the CLSI M07-A11 January 2018 agar microdilution reference method, following rules as defined in the FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA, issued on August 28, 2009 and following specifications as defined in CLSI M100 30th Ed. (January 2020)."

While specific numerical acceptance thresholds are not explicitly listed in the document for Essential Agreement (EA) and Category Agreement (CA), the reported performance is presented as meeting acceptable levels. The predicate device also states "Meets Guidance Document Performance Requirements: Yes." This implies the acceptance criteria for EA and CA were those outlined in the referenced FDA Guidance Document and CLSI standards.

1 EA = % of MIC values within ± 1 dilution of the reference method.
2 CA = Correct determination of susceptibility category (e.g., Susceptible, Intermediate, Resistant)

2. Sample size used for the test set and the data provenance

• Test Set Sample Size:
  • Enterococcus faecalis: 191 strains
  • Escherichia coli: 238 strains
• Data Provenance: The document states "External evaluations were conducted with fresh and stock clinical isolates, as well as a set of challenge strains." This indicates the data is retrospective (using existing clinical isolates and stock cultures) and likely prospective (fresh clinical isolates). The country of origin is not explicitly stated, but bioMérieux is a French company.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts

This information is not applicable to this type of device and study. The ground truth for antibiotic susceptibility testing (AST) devices is established by a standardized, laboratory-based reference method (CLSI agar microdilution method), not by human expert opinion or consensus.

4. Adjudication method for the test set

Not applicable. The ground truth is determined by a standardized laboratory method, not by human interpretation requiring adjudication.

5. If a multi-reader multi-case (MRMC) comparative effectiveness study was done, if so, what was the effect size of how much human readers improve with AI vs without AI assistance

Not applicable. This device is an in-vitro diagnostic for antimicrobial susceptibility testing. It does not involve human readers interpreting images, nor does it incorporate AI assistance in the way typically seen in radiology or ophthalmology devices. The comparison is between the test device (ETEST) and a laboratory reference method (CLSI agar microdilution).

6. If a standalone (i.e., algorithm only without human-in-the-loop performance) was done

This concept is also not directly applicable in the same way it would be for an AI algorithm interpreting images. The ETEST operates as a "standalone" laboratory test in that its result (the MIC value) is read directly from the strip after incubation. There isn't an "algorithm" in the typical AI sense; rather, it's a defined chemical gradient interaction with bacterial growth. The performance study evaluates the device's accuracy in determining MIC and category agreement compared to a reference method, which is essentially its "standalone" performance.

7. The type of ground truth used

The ground truth used was the CLSI (Clinical and Laboratory Standards Institute) M07-A11 January 2018 agar microdilution reference method. This is a laboratory-based reference method widely accepted as the gold standard for antimicrobial susceptibility testing. It's not expert consensus, pathology, or outcomes data in this context.

8. The sample size for the training set

The document does not explicitly state the sample size used for a "training set." This type of regulatory submission outlines the performance of the device against a reference method, which corresponds to what would typically be a "test set" in an AI/ML context. For a device like ETEST, which is a physical consumable strip with a pre-defined chemical gradient, there isn't a traditional "training" phase for an algorithm in the way a machine learning model would be trained. The development and optimization of the gradient would occur during product development, but this information is not part of the 510(k) submission.

9. How the ground truth for the training set was established

As described in point 8, there isn't a "training set" in the machine learning sense for this device. The physical characteristics and performance of the ETEST strip are developed and characterized, and then validated against the CLSI reference method. The "ground truth" for evaluating the performance of the final device (the "test set") is consistently the CLSI agar microdilution reference method.

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