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The APAS Compact is an in vitro diagnostic system comprised of an instrument for automated imaging of agar culture plates and a software analysis module for the following use:

The APAS Compact, when using its urine analysis module, automates urine culture plate imaging and interpretation to detect the presence of microbial growth on sheep blood and MacConkey agar culture plates that are inoculated with a 1uL sample volume. The APAS Compact, when using its urine analysis module, provides a semiquantitative assessment of colony counts that are used as an aid in the diagnosis of urinary tract infection. All urine culture plates that are identified as positive for growth by the APAS Compact, when using its urine analysis module, must be reviewed by a trained microbiologist.

The APAS Compact with Urine Analysis Module is an instrumented system that is designed for screening of urine culture plates for the presence of microbial growth. The device comprises an imaging station for capture of digital images of the culture plates, together with software for analysis of the images, the determination and enumeration of microbial growth and reporting of results.

This document outlines the acceptance criteria and study findings for the APAS Compact with Urine Analysis Module.

1. Acceptance Criteria and Reported Device Performance

2. Sample Sizes and Data Provenance

• Test Set (Clinical Study):

  • Total Enrolled Samples: 10,100 urine samples (5835 from Site 1, 2117 from Site 2, 2148 from Site 3).
  • Included in Performance Analysis: 9,224 samples (5634 from Site 1, 1769 from Site 2, 1821 from Site 3).
  • Data Provenance: Three clinical sites: one in the US (Site 1) and two ex-US (Sites 2 and 3). The study used remnant urine samples from standard of care culture. This indicates a retrospective data collection approach for the clinical study.

• Training Set: The document does not explicitly state the sample size for the training set.

3. Number of Experts and Qualifications for Ground Truth (Test Set)

• Number of Experts: Three microbiologists.
• Qualifications: "Trained microbiologist" is mentioned multiple times. For the clinical study, each microbiologist was "trained to read the urine culture plates in a standard fashion." Specific years of experience are not provided.

4. Adjudication Method (Test Set)

• The document states that for the reference method in the clinical study, "each microbiologist... was blinded to the results from the other panel members and to those obtained by the APAS Compact."
• The ground truth for the clinical study was established by a "reference microbiologist panel," meaning the consensus among these three microbiologists. The exact method of achieving consensus (e.g., 2+1, 3+1, none) is not explicitly detailed, but it implies a shared understanding to form the "reference method."

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

• No, a MRMC comparative effectiveness study was not done. The clinical study compared the APAS Compact's performance against a panel of microbiologists (serving as the reference standard), not against human readers with and without AI assistance to measure improvement. The primary goal of the APAS Compact is to automate initial screening to reduce microbiologist workload, rather than directly augment human reading for every plate.

6. Standalone Performance Study

• Yes, a standalone performance study was done. The entire clinical study (Section L.3) and analytical performance studies (Section L.1) evaluate the APAS Compact's performance as an algorithm-only device (without human-in-the-loop during the initial assessment and designation phase). The performance tables (e.g., Tables 19-24) directly report the APAS Compact's designations and colony counts compared to the reference standard. While the device's indications for use emphasize that growth-positive plates "must be reviewed by a trained microbiologist," the reported performance metrics are for the algorithm's initial assessment before this mandatory human review.

7. Type of Ground Truth Used

• Clinical Study: Expert Consensus (Microbiologist Panel): The ground truth for the clinical study was established by "an independent panel of three microbiologists," who read the urine culture plates in a "standard fashion" and were blinded to other results. Their combined assessment served as the reference method.
• Analytical Study (Linearity/Assay Reportable Range): Expert Consensus (Manual Colony Counts): The mean of two independent manual colony counts performed by two microbiologists was used as the reference result for each plate.

8. Sample Size for the Training Set

• The document does not explicitly state the sample size for the training set. It describes the "APAS Controller Software" and "Urine Analysis Module Software" functions, implying that these algorithms were developed and likely trained, but the specific training data volume is not provided in this excerpt.

9. How Ground Truth for the Training Set Was Established

• The document does not explicitly describe how the ground truth for the training set was established. While it details the methods for establishing ground truth in the analytical and clinical validation studies (using expert microbiologist consensus), it does not provide information specific to the data used for training the algorithms.

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