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Evaluation of two ELISA tests for the rapid detection of group A streptococci
P Egger1, C A Siegrist, G Strautmann
1Paediatric Clinic, University Hospital, Geneva, Switzerland.
Insights
The TestPack Strep A (TPSA) ELISA test is highly specific for group A streptococcal antigen detection in children with pharyngitis. However, its sensitivity is insufficient for reliably ruling out infections.
Area of Science:
- Clinical microbiology
- Diagnostic immunology
Background:
- Group A Streptococcus (GAS) is a common cause of bacterial pharyngitis in children.
- Accurate and rapid diagnosis of GAS is crucial for appropriate antibiotic treatment and preventing complications.
Purpose of the Study:
- To compare the diagnostic performance of two rapid ELISA tests, TestPack Strep A (TPSA) and Direct Strep A EIA (DSAE), against anaerobic sheep blood agar culture for GAS antigen detection.
- To evaluate the sensitivity, specificity, and predictive values of TPSA and DSAE in pediatric pharyngitis cases.
Main Methods:
- Analysis of 579 oropharyngeal swab specimens from children with pharyngitis.
- Comparison of TPSA and DSAE test results with results from anaerobically incubated sheep blood agar cultures.
Main Results:
- TPSA demonstrated a sensitivity of 60.8% and specificity of 98.3%.
- DSAE showed a sensitivity of 64.4% and specificity of 93.2%.
- Positive predictive values were 88.6% for TPSA and 70.3% for DSAE; negative predictive values were 92.0% for TPSA and 91.2% for DSAE.
Conclusions:
- TPSA is easy to interpret and highly specific, supporting treatment initiation for positive results.
- Neither TPSA nor DSAE possess sufficient sensitivity to reliably exclude GAS pharyngitis with negative or intermediate results.
- DSAE performance is comparable to TPSA but with slightly lower specificity and a higher rate of false positives.
Abstract:
We examined 579 oropharyngeal swab specimens from children presenting with pharyngitis in order to compare two rapid diagnostic ELISA tests for group A streptococcal antigen: the TestPack Strep A (TPSA), and the Direct Strep A EIA (DSAE), with an anaerobically incubated sheep blood agar culture. The sensitivities of the methods were respectively 60.8% (TPSA) and 64.4% (DSAE), the specificities 98.3% (TPSA) and 93.2% (DSAE), the positive predictive values 88.6% (TPSA) and 70.3% (DSAE) and the negative predictive values 92.0% (TPSA) and 91.2% (DSAE). We conclude that the TPSA is easy to interpret and is sufficiently specific to initiate treatment in patients with a positive test. It is not sufficiently sensitive to ensure negative or intermediate results. The performance of the DSAE test is similar but the specificity is slightly lower and more false positive results occur.