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Detection of group a streptococcal pharyngitis by quantitative PCR
Eileen M Dunne1, Julia L Marshall, Ciara A Baker
1Pneumococcal Research, Murdoch Childrens Research Institute, Parkville, VIC, Australia. eileen.dunne@mcri.edu.au
Insights
A new speB quantitative polymerase chain reaction (qPCR) assay accurately detects Group A Streptococcus (GAS) pharyngitis in children. This rapid qPCR test offers high sensitivity and specificity for diagnosing GAS infections, improving clinical outcomes.
Area of Science:
- Microbiology
- Infectious Diseases
- Molecular Diagnostics
Background:
- Group A Streptococcus (GAS) is a common cause of bacterial pharyngitis, particularly in school-aged children.
- Current diagnostic methods, including culture, are time-consuming (24-48 hours) and can be complicated by asymptomatic GAS carriage.
- Developing rapid and accurate diagnostic tools for GAS pharyngitis is crucial for timely treatment and infection control.
Purpose of the Study:
- To develop and evaluate a quantitative polymerase chain reaction (qPCR) assay for the detection of GAS in pharyngeal swabs.
- To assess the suitability of the developed qPCR assay for clinical diagnosis of GAS pharyngitis.
Main Methods:
- Pharyngeal swabs were collected from children and adults presenting with sore throat.
- Two candidate PCR assays targeting speB and spy1258 genes were developed into qPCR assays.
- qPCR results were compared against standard culture-based methods for GAS detection; emm-typing and McIsaac scores were also utilized.
Main Results:
- The speB qPCR assay demonstrated 100% sensitivity and 100% specificity compared to culture.
- The spy1258 qPCR assay showed 87% sensitivity and 100% specificity.
- GAS was identified in 18.9% of samples, exclusively in children (26%); nine emm types were identified, with emm 89, 3, and 28 being most prevalent.
Conclusions:
- The speB qPCR assay is a highly sensitive and specific tool for diagnosing GAS pharyngitis.
- This qPCR method shows promise for improving the clinical diagnosis and research of GAS infections.
Background:
Group A streptococcus (GAS) is the most common bacterial cause of sore throat. School-age children bear the highest burden of GAS pharyngitis. Accurate diagnosis is difficult: the majority of sore throats are viral in origin, culture-based identification of GAS requires 24-48 hours, and up to 15% of children are asymptomatic throat carriers of GAS. The aim of this study was to develop a quantitative polymerase chain reaction (qPCR) assay for detecting GAS pharyngitis and assess its suitability for clinical diagnosis.
Methods:
Pharyngeal swabs were collected from children aged 3-18 years (n = 91) and adults (n = 36) located in the Melbourne area who presented with sore throat. Six candidate PCR assays were screened using a panel of reference isolates, and two of these assays, targeting speB and spy1258, were developed into qPCR assays. The qPCR assays were compared to standard culture-based methods for their ability to detect GAS pharyngitis. GAS isolates from culture positive swabs underwent emm-typing. Clinical data were used to calculate McIsaac scores as an indicator of disease severity.
Results:
Twenty-four of the 127 samples (18.9%) were culture-positive for GAS, and all were in children (26%). The speB qPCR had 100% sensitivity and 100% specificity compared with gold-standard culture, whereas the spy1258 qPCR had 87% sensitivity and 100% specificity. Nine different emm types were found, of which emm 89, 3, and 28 were most common. Bacterial load as measured by qPCR correlated with culture load. There were no associations between symptom severity as indicated by McIsaac scores and GAS bacterial load.
Conclusions:
The speB qPCR displayed high sensitivity and specificity and may be a useful tool for GAS pharyngitis diagnosis and research.
