(83 days)
The BioStar® STREP B OIA® assay is an Optical ImmunoAssay (OIA) test for the rapid detection of group B streptococcal antigen directly from cervical and vaginal swabs from intrapartum maternity patients. The STREP B OIA assay is intended for use as an adjunct to culture, clinical observation and other information available to the physician.
The STREP B OlA test involves the extraction of a carbohydrate antigen unique to group B Streptococi from the cervical or vaginal swab specimen and the subsequent use of Optical ImmunoAssay technology for the qualitative detection of this specific antigen. The Optical ImmunoAssay technology allows the direct visual detection of the physical change in optical thickness of molecular thing from the binding reactions between antibodies and antigens. The signal is generated by the reflection of light through the molecular thin films formed on an optical substrate. White light reflected through the molecular thin film results in a predominant visual background gold color. This color will not change unless the thickness of the optical molecular thin film is changed. When a liquid sample containing antigen from group B Streptococci is placed on the test surface, binding occurs between the antigen and immobilized antibody, causing an increased thickness in the molecular this reaction takes place, the optical path through the film is changed, causing a corresponding change in the gold color to purple/blue, thereby indicating a positive result. The change in optical thickness is due to the binding of specific antigen. If the antigen is not present in the sample, no binding takes place. The original molecular thickness remains unchanged and the test surface retains its original gold color, indicating a negative result. The clear endpoint and unequivocal results observed with the optical detection system lead to a very sensitive easily interpreted assay system.
Here's an analysis of the provided text, outlining the acceptance criteria and study details for the STREP B OIA® device:
1. Table of Acceptance Criteria and Reported Device Performance
The document does not explicitly state pre-defined acceptance criteria in terms of sensitivity and specificity targets. However, the study results are presented with 95% Confidence Intervals (CI), which implicitly define a range of acceptable performance. The performance is reported in comparison to "Lim Broth Culture" as the reference standard.
| Performance Metric | Acceptance Criteria (Implied by 95% CI) | Reported Device Performance (STREP B OIA® vs. Lim Broth) |
|---|---|---|
| Sensitivity | 56.7% - 70.5% | 63.8% |
| Specificity | 91.3% - 95.0% | 93.3% |
Note: The document also reports sensitivity for "TSA Culture to Lim Broth Culture" for comparison, which achieved a sensitivity of 60.8% (CI: 53.7-67.6%) and specificity of 99.6% (CI: 98.8-99.9%). This suggests that the STREP B OIA®'s performance falls within a similar range of what would be expected from a non-selective culture method compared to a selective broth culture.
2. Sample Size Used for the Test Set and Data Provenance
- Sample Size for Test Set: 947 samples (cervical and vaginal swabs).
- Data Provenance: The study was a "prospective evaluation of clinical specimens taken from women." The country of origin is not explicitly stated, but the submission is to the FDA (USA), implying the study was likely conducted in the USA or adhering to US regulatory standards.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts
The ground truth was established by microbiological culture methods (Lim broth culture and TSA culture), not by human experts interpreting results. The document does not mention the number or qualifications of personnel performing these lab procedures.
4. Adjudication Method for the Test Set
No explicit adjudication method (like 2+1 or 3+1 consensus) was used, as the ground truth was determined by laboratory culture results.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done
No, an MRMC comparative effectiveness study was not done. This device is a rapid diagnostic test intended for laboratory use, not typically requiring human reader interpretation in the same way as imaging studies. The study compared the device's performance to a laboratory reference standard.
6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done
Yes, this study represents a standalone performance evaluation of the STREP B OIA® device. The device itself produces a clear visual positive or negative result, which is then recorded. The performance metrics presented are based on the device's output compared to the reference standard, without any human interpretation of the device's optical changes being part of the reported performance.
7. The Type of Ground Truth Used
The primary ground truth used for establishing clinical performance was Lim broth culture, which is a selective broth culture method considered a more sensitive reference standard for Group B Strep detection compared to direct agar culture. The document also mentions comparison to "routine microbiological Trypticase Soy Agar with 5% Sheep Blood (TSA) culture media" as an initial step.
8. The Sample Size for the Training Set
The document does not explicitly mention a separate "training set" or its size. In vitro diagnostic devices like the STREP B OIA® are typically developed and optimized by the manufacturer, and then clinical performance is assessed on a distinct set of samples. The study described in section H is referred to as a "clinical testing" or "clinical evaluation," implying it serves as the validation dataset.
9. How the Ground Truth for the Training Set Was Established
Since no separate training set is explicitly mentioned, the method for establishing ground truth for the clinical evaluation (which serves as the basis for performance claims) was as follows:
- Cervical and vaginal specimens were collected using dual swabs.
- One swab was either:
- Plated directly onto TSA within 24 hours of collection.
- The pledget from the swab was placed in Lim broth, incubated, and then subcultured (10 ul) at 18-24 hours to a TSA plate.
- All plates were incubated, and beta-hemolytic streptococcal colonies were selected and confirmed using a streptococcal group serotyping method.
- Lim broth culture was identified as the reference standard against which the STREP B OIA®'s performance was compared.
§ 866.3740
Streptococcus spp. serological reagents.(a)
Identification. Streptococcus spp. serological reagents are devices that consist of antigens and antisera (excluding streptococcal exoenzyme reagents made from enzymes secreted by streptococci) used in serological tests to identifyStreptococcus spp. from cultured isolates derived from clinical specimens. The identification aids in the diagnosis of diseases caused by bacteria belonging to the genusStreptococcus and provides epidemiological information on these diseases. Pathogenic streptococci are associated with infections, such as sore throat, impetigo (an infection characterized by small pustules on the skin), urinary tract infections, rheumatic fever, and kidney disease.(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 § 866.9.