Poster Presentation Lorne Infection and Immunity 2013

Detection of group A streptococcus pharyngitis by quantitative PCR (#117)

Eileen M Dunne 1 , Ciara Baker 1 , Julia Marshall 1 , Jayne Manning 1 , Margaret Danchin 1 , Pierre Smeesters 1 , Catherine Satzke 1 , Andrew Steer 1
  1. Murdoch Childrens Research Institute, Parkville , VIC, Australia

Group A streptococcus (GAS; Streptococcus pyogenes) is a Gram positive bacterium that causes a wide range of diseases, including pharyngitis, invasive skin infections, scarlet fever, and serious post-infection sequelae such as acute rheumatic fever.  GAS is the most common bacterial cause of sore throat (‘pharyngitis’), and school-age children bear the highest burden of GAS pharyngitis.  Accurate diagnosis of GAS is difficult: the majority of sore throat is viral in origin, identification of GAS by culture typically requires 24-48 h, and approximately 15% of children are asymptomatic carriers of GAS.   At present there is no standard quantitative PCR (qPCR) test for GAS.  Such a test may be able to differentiate between carriage and pharyngitis based upon bacterial load and enable investigation of the relationship between GAS bacterial loads, symptom severity, viral co-infection, and immune response.   The aim of this study was to develop and optimise a real-time qPCR assay for detecting GAS pharyngitis, and to investigate associations between GAS bacterial loads, emm type, and symptom severity.  Using reference isolates, two target gene candidates, speB and spy1258, were selected from a panel of six qPCR assays for use in the pharyngitis study.  Pharyngeal swabs were collected from children aged 2 – 18 years (n=92) in the Melbourne area presenting with sore throats, and GAS detected by qPCR and compared with the gold-standard culture method.  The speB qPCR had 100% specificity and 100% sensitivity, whereas the spy1258 qPCR had 100% specificity and 88% sensitivity, as it did not detect GAS in 3 of 24 culture-positive samples.  Therefore, the speB qPCR will be used to investigate associations between GAS bacterial loads, emm type, and symptom severity.