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Evaluating clinical decision rules and rapid diagnostic tests for the diagnosis of Streptococcus pyogenes pharyngitis
Edwin P Armitage1, Elina Senghore2, Fatoumata E Camara2
1Vaccines and Immunity Theme, Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, Gambia; Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London WC1E 7HT, UK; Population Health Sciences, University of Bristol, Bristol BS8 2BN, UK.
Insights
Rapid diagnostic tests and clinical decision rules showed poor performance for Streptococcus pyogenes pharyngitis in The Gambia. Molecular methods offer higher accuracy, highlighting the need for better diagnostics in resource-limited settings.
Area of Science:
- Infectious Diseases
- Microbiology
- Diagnostics
Background:
- Accurate diagnosis of Streptococcus pyogenes (S. pyogenes) pharyngitis is crucial in countries with high rheumatic heart disease burden.
- Current diagnostic methods in resource-limited settings may not be sufficiently sensitive or specific.
Purpose of the Study:
- To evaluate the diagnostic accuracy of two rapid diagnostic tests (RDTs) and five clinical decision rules (CDRs) for S. pyogenes pharyngitis in The Gambia.
- To compare the performance of RDTs and CDRs against culture and molecular methods (qPCR).
Main Methods:
- Children under 16 with pharyngitis symptoms were recruited in The Gambia.
- Diagnostic accuracy of a rapid antigen detection test (LFT) and a rapid gene-amplification test (ID NOW) was assessed against culture and qPCR.
- Five CDRs were evaluated, and logistic regression identified risk factors for S. pyogenes pharyngitis.
Main Results:
- Molecular methods (PCR) detected a higher prevalence of S. pyogenes (32.4%) compared to culture (9.8%).
- The ID NOW test demonstrated high sensitivity (93.5-94.6%) but variable specificity (73.6-87.6%).
- The LFT showed lower sensitivity (55.7-83.8%) and variable specificity (74.0-80.0%). The Smeesters CDR had the best performance among CDRs (AUC 0.694). Age, recent chest infection, and concurrent skin infection were associated with increased risk.
Conclusions:
- Rapid diagnostic tests and clinical decision rules exhibited poor performance for S. pyogenes pharyngitis detection in this setting.
- Molecular methods are superior to culture for identifying S. pyogenes.
- There is an urgent need for affordable and sensitive diagnostic tools for effective management of S. pyogenes in resource-limited areas.
Objectives:
Accurate diagnosis of Streptococcus pyogenes (S. pyogenes) pharyngitis is imperative in high rheumatic heart disease-burden countries. We aimed to assess the diagnostic accuracy of two rapid diagnostic tests and five clinical decision rules (CDRs) in The Gambia.
Methods:
Children under 16 years presenting with signs and symptoms of pharyngitis were recruited at Sukuta Health Centre, The Gambia. A rapid antigen detection test (SD Bioline; LFT) and a rapid gene-amplification test (ID NOW™ STREP A2) were assessed for diagnostic accuracy alongside five CDRs against culture and qPCR for S. pyogenes. Logistic regression was used to determine risk factors for S. pyogenes pharyngitis.
Results:
Among 376 participants, S. pyogenes positivity was 9·8% (37/376) by culture, 32·4% (122/376) by PCR, 31·6% (119/376) by LFT, and 33·3% (122/366) by ID NOW. The ID NOW had sensitivities and specificities of 94·6% and 73·6% against culture, and 93·5% and 87·6% against PCR. The LFT had sensitivities and specificities of 83·8% and 74·0% against culture and 55·7% and 80·0% against PCR. The Smeesters CDR performed best with an area under the curve (AUC) of 0·694 against culture. S. pyogenes pharyngitis risk increased with age. Recent chest infection/cough (aOR 1·89, 1·08-3·28) and concurrent skin infection (aOR 2·11, 1·21-3·69) were associated with increased S. pyogenes pharyngitis.
Conclusions:
The LFT and the CDRs had poor performance in detecting S. pyogenes pharyngitis compared to PCR and culture. Molecular methods detected a higher proportion of S. pyogenes than culture. Affordable and sensitive diagnostics are urgently needed to improve S. pyogenes management in resource-limited settings.
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