Related Experiment Videos
Comparison of Gen-Probe Group A streptococcus Direct Test with culture for diagnosing streptococcal pharyngitis
S J Pokorski1, E A Vetter, P C Wollan
1Department of Laboratory Medicine, Mayo Clinic, Rochester, Minnesota 55905.
Abstract:
The Group A Streptococcus Direct Test (GP-ST test; Gen-Probe, Inc., San Diego, Calif.) was compared with culture for the detection of Streptococcus pyogenes from throat swabs of 767 patients with pharyngitis. Swabs were tested by the GP-ST test after inoculating a 5% sheep blood agar (SBA) plate. SBA plates were incubated at 35 degrees C in room air for 72 h. SBA plates with no evidence of beta-hemolytic colonies after 18 to 24 h of incubation were subcultured by taking a swipe across the primary inoculum from the SBA plate to an agar selective for Streptococcus spp. In a low-prevalence (11.9%) population and in comparison with the number of positive cultures detected by the 72-h single-culture method (SBA plate method), the GP-ST test had a sensitivity of 88.6%, a specificity of 97.8%, a positive predictive value of 83.9%, and a negative predictive value of 98.5%. In comparison with the growth of any colonies of S. pyogenes on the 72-h SBA plates plus a subculture onto selective blood agar, the sensitivities and specificities were as follows: 72-h SBA plate method, 96.7 and 100%, respectively; GP-ST test, 85.7 and 97.8%, respectively. The GP-ST test is an easy-to-perform, reliable test for batch screening of throat swabs for S. pyogenes.
Insights
The Group A Streptococcus Direct Test (GP-ST test) offers a reliable method for detecting Streptococcus pyogenes in throat swabs. This test is suitable for batch screening, providing accurate results for pharyngitis diagnosis.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Infectious Diseases
Background:
- Group A Streptococcus (GAS) is a common cause of pharyngitis.
- Accurate and rapid diagnostic methods are crucial for effective treatment and prevention of GAS complications.
- Traditional culture methods can be time-consuming.
Purpose of the Study:
- To evaluate the performance of the Group A Streptococcus Direct Test (GP-ST test) compared to standard culture methods for detecting Streptococcus pyogenes.
- To assess the sensitivity, specificity, and predictive values of the GP-ST test in a clinical setting.
Main Methods:
- A comparative study involving 767 patients with pharyngitis.
- Throat swabs were tested using the GP-ST test and simultaneously inoculated onto 5% sheep blood agar (SBA) plates.
- SBA plates were incubated for 72 hours, with subculturing onto selective agar for Streptococcus spp. if initial growth was not observed within 18-24 hours.
Main Results:
- In a low-prevalence population, the GP-ST test showed a sensitivity of 88.6% and specificity of 97.8% compared to the 72-h single-culture method.
- When compared to a more comprehensive 72-h culture with subculture, the GP-ST test demonstrated a sensitivity of 85.7% and specificity of 97.8%.
- The GP-ST test exhibited high negative predictive value (98.5%) in the low-prevalence setting.
Conclusions:
- The GP-ST test is an easy-to-perform and reliable diagnostic tool for Streptococcus pyogenes detection.
- It is well-suited for batch screening of throat swabs in clinical laboratories.
- The test provides valuable data for the diagnosis of pharyngitis caused by Streptococcus pyogenes.