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Para-Fix™ C&S Medium provides a method for collecting and preserving fecal specimens for the culture of intestinal enteric bacteria. Because the medium is capable of maintaining the bacteria for 96 hours, immediate transportation and processing of the specimen is not necessary.

Para-Fix C&S Medium is a non-nutritive, buffered, isotonic solution with a pH indicator added. The medium also contains agar and sodium thioglycolate to maintain a low oxygen tension for the preservation of anaerobic species. The phenol red indicator will turn yellow when the solution is acidic and the conditions are not optimal for recovery of the intended organisms. Each 30 mL vial contains 15 ml of solution and a built in sample collection spoon. The kit is available with or without a multilingual instruction sheet and re-sealable bag.

Here's a breakdown of the acceptance criteria and the studies performed for the MCC Para-Fix C&S Medium, based on the provided document:

Acceptance Criteria and Reported Device Performance

• Without Fecal Matrix (Swab Elution Method): All 10 tested enteric organisms (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella enterica, Bacillus subtilis, Vibrio parahaemolyticus, Clostridium difficile, Campylobacter jejuni, Enterococcus faecalis, Shigella dysenteriae) showed log reduction/increase values well within the ±2 log10 criterion after 96 hours at both 2-8°C and 20-25°C. The maximum observed log change was 1.34 (Pseudomonas aeruginosa at 20-25°C), and the minimum was -0.02 (Salmonella enterica at 2-8°C).
• With Fecal Matrix (Roll-Plate Method): Salmonella enterica, Vibrio parahaemolyticus, and Escherichia coli generally showed log reduction/increase values within the ±2 log10 criterion after 120 hours at 2-8°C. (Note: Many results at 72, 96, and 120 hours for 20-25°C were "Too numerous to count," indicating significant growth, which still suggests preservation and recovery).
• With Fecal Matrix (Swab Elution Method): Salmonella enterica, Vibrio parahaemolyticus, and Escherichia coli generally showed log reduction/increase values within the ±2 log10 criterion after 120 hours at both 2-8°C and 20-25°C. Max log increase was +0.88, max log reduction was -0.23. |
  | Shelf-Life Stability: The product must maintain bacteria inocula (within ±2 log10 of original counts) on vials exceeding the 18-month expiration dating (worst-case condition). | Met: Bacterial counts for newly manufactured vials and vials exceeding expiration dating were within ±2 log10 of the original inoculum at the time of inoculation and 96 hours later. |
  | Bioburden: No viable organisms should be present. Absence of Gram-positive or Gram-negative organisms by Gram staining. | Met: No viable organisms found in any lots tested at time of manufacture. No Gram-positive or Gram-negative organisms detected after end of expiration dating by Gram staining. |
  | pH Value: pH of the product should be within an acceptable range. | Met: pH value at the time of testing was between 7.08 to 7.83. (Acceptable range is implied by compliance with the predicate device and functional performance). |
  | Vial Pressure Test: 95 kPa. | Met: Vial pressure test reported as 95 kPa. |
  | Container: 30 mL Vial. | Met: 30 mL Vial. |
  | Closure: Screw cap & spork. | Met: Screw cap & spork. |
  | Formulation: Cary Blair - modified. | Met: Cary Blair - modified. |
  | Fill Volume: 15 mL. | Met: 15 mL. |
  | Storage Temperature: 20-30°C. | Met: 20-30°C. (The study tested 2-8°C and 20-25°C which falls within this range). |
  | Buffer System: Phosphate. | Met: Phosphate. |
  | Oxygen Tension: Thioglycolate. | Met: Thioglycolate. |
  | pH Indicator: Phenol red. | Met: Phenol red. |

Study Information

1. Sample Size used for the test set and the data provenance:

   • Test Set (without fecal matrix): The specific number of replicates per organism and temperature condition is not explicitly stated, but the tables provide "Average CFU's Recovered," implying multiple measurements. There were 10 different enteric organisms tested at two temperature conditions (2-8°C and 20-25°C).
   • Test Set (with fecal matrix): For the "Representative Enteric organism recovery results for Para-Fix™ C&S Medium using Roll-Plate Method" and "Swab Elution Method", three organisms were tested (Salmonella enterica, Vibrio parahaemolyticus, Escherichia coli) at two temperature conditions, with measurements at 0, 72, 96, and 120 hours. Again, "Average CFU's Recovered" implies multiple runs.
   • Data Provenance: The study used "clinically negative human fecal matrix." No specific country of origin is mentioned, but it is a laboratory study, likely prospective, evaluating the performance of the device under controlled conditions.

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

   • Not applicable for this type of performance study. The ground truth (initial bacterial counts and subsequent counts after storage) was established through quantitative microbiological methods (plate counts, CFU determination) performed in a laboratory, rather than expert interpretation of a diagnostic outcome.

3. Adjudication method for the test set:

   • Not applicable. This is a quantitative laboratory performance study, not a clinical study involving human interpretation or consensus.

4. 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 a transport medium for laboratory samples, not an AI-assisted diagnostic tool requiring human reader studies.

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

   • Yes, this was a standalone performance study of the physical device (transport medium). There is no "algorithm" or "human-in-the-loop" component. The device's ability to preserve organisms was tested directly.

6. The type of ground truth used (expert consensus, pathology, outcomes data, etc.):

   • Quantitative Microbiological Analysis: The ground truth was based on quantitative culture results (Colony Forming Units - CFUs) obtained through standard laboratory techniques (plate counts, swab elution, roll-plate methods) for specific bacterial organisms under controlled conditions. This is a direct measurement of the device's functional performance.

7. The sample size for the training set:

   • Not applicable. This is not a machine learning or AI-based device, so there is no training set in that context. The "training" of the medium itself is its chemical formulation and manufacturing process.

8. How the ground truth for the training set was established:

   • Not applicable, as there is no training set in the context of an algorithmic or AI device. The "ground truth" for the device's design and formulation would have been established through traditional microbiology and chemistry research and development, aiming to meet established standards like CLSI M40-A2 for transport media.

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