# Evaluation of a fully automated “sample-to-result” PCR-based diagnostic test for detecting A/C/G Streptococci from throat swab specimens

## TL;DR

A fully automated PCR test for detecting throat streptococci is faster and reliable, especially for ruling out infections.

## Contribution

The study evaluates a new automated PCR method for rapid detection of A/C/G Streptococci in throat swabs.

## Key findings

- The PCR test showed 94.1% sensitivity and 94.2% specificity for detecting GAS, GCS, and GGS.
- The negative predictive value was high at 98.5%, making it effective for ruling out infections.
- PCR reduces turnaround time and could help reduce unnecessary antibiotic use.

## Abstract

Group A Streptococcus (GAS) and group C/G Streptococcus (GCS/GGS) species cause bacterial pharyngitis in both adults and children. Occasionally, GAS can cause invasive and severe infections like septicemia, streptococcal toxic shock-like syndrome, and necrotizing fasciitis. Throat culture has remained the gold standard method for diagnosing GAS or GCS/GGS pharyngitis. Methodologically, bacterial cultivation is laborious and time-consuming. For this, nucleic acid-based tests have been developed since they are rapid and have high sensitivity and specificity compared to culture methods. However, only a few molecular methods for the detection of GAS and especially for GCS/GGS in clinical throat swab specimens have been described. This study compares the clinical and analytical performance of a fully automated “sample-to-result” PCR with the gold standard reference method, culture. According to our results, the sensitivity of pooled PCR for GAS, GCS, and GGS was 94.1%, and the specificity was 94.2%. Pooled positive predictive value was 80.0%, and the negative predictive value was 98.5%. These results highlight that PCR is a reliable method, especially for ruling out negative cases due to its high negative predictive value. However, its positive predictive value is lower, meaning there is a higher chance of false positives. A PCR-based method for the diagnosis of pharyngitis would speed up turnaround time (TAT) and automate laboratory processes, especially in locations far away from a central laboratory. Faster TAT with a sensitive and specific method could reduce unnecessary antibiotic use, since currently, clinicians often prescribe antibiotics empirically before final test results.

Pharyngitis is commonly caused by viruses or by Streptococci, the latter of which can be treated with antibiotics. Rapid differential diagnostics help to reduce unnecessary antibiotic use, as clinicians often initiate empirical treatment before culture results are available. In addition, a shorter turnaround time for laboratory diagnosis may prevent transmission or development of the more severe disease. Diagnosis of streptococcal pharyngitis is commonly done by culture, which requires at least 24 h incubation. The results of our study showed that the fully automated PCR system is a useful and reliable tool for speeding up the diagnosis and would be helpful, especially in locations far away from central laboratories.