Virtual Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

qPCR enhances detection of Strep A in skin and throat specimens from children at higher risk of disease (#216)

Bernadette Wong 1 , Timothy C. Barnett 1 2 , Scott Winslow 1 , Dylan D. Barth 1 , Jonathan R. Carapetis 1 3 , Asha C. Bowen 1 3 4 , Janessa L. Pickering 1
  1. Wesfarmer’s Centre for Vaccines and Infectious Diseases, Telethon Kids Institute, Nedlands, Western Australia, Australia
  2. School of Biomedical Sciences, The University of Western Australia, Nedlands, WA, Australia
  3. Centre for Child Health Research, University of Western Australia, Nedlands, Western Australia, Australia
  4. Department of Infectious Diseases, Perth's Children Hospital, Nedlands, Western Australia, Australia

Background:

Streptococcus pyogenes (S. pyogenes; Group A Streptococcus; Strep A) is a gram-positive bacterium which causes a range of localised, severe, and autoimmune diseases. Rheumatic heart disease (RHD) is a major cause of Strep A mortality, with Aboriginal and Torres Strait Islander people 60 times more likely to live with acute rheumatic fever and RHD. Therefore, children living in remote Australian communities are disproportionately affected by Strep A diseases. More accurate Strep A laboratory detection from clinical swab specimens is required to understand the prevalence and biology, which consequently determine treatment approaches.

We aimed to further interrogate samples from a cohort of school children enrolled in our surveillance study  based in remote Western Australia (Kimberley region).   

 

Methods:

Demographics, clinical data and specimens were obtained during the school-based surveillance programme. In 2019, 470 skin and throat swabs stored in Skim-Milk-Glucose-Glycerol-Broth were collected and underwent gold standard Strep A culture. We optimised and performed Strep A DNA extraction and speB quantitative PCR (qPCR) directly on a subset of clinical skin (n=32) and throat swabs (n=289) to determine Strep A bacterial load, then evaluated against culture results.

 

Results:

Strep A qPCR showed a sensitivity and specificity of 97.70% (95% CI [88.2 to 99.6]) and 77.50% (95% CI [71.9 to 82.3]) for throat swabs relative to culture results. The reduced specificity resulted from an additional 55 culture-negative throat samples that were Strep A positive by qPCR, demonstrating increased detection capability and potential for high-throughput analysis of large cohorts. Furthermore, speB qPCR resulted in a shorter turnaround time compared to culture. speB Cq values did not differentiate Strep A pharyngitis and carriage (p=0.938).

 

Conclusions:

The enhanced detection with molecular technology should be considered in laboratory surveillance of Strep A infections. Detection and prevention of Strep A diseases remains crucial to RHD elimination.

  1. Med J Aust. 2016; 205(5): 201 203. May et al. The inequitable burden of group A streptococcal diseases in Indigenous Australians.
  2. BMC Ear Nose Throat Disord. 2006; 6: Smith Vaughan et al. Measuring nasal bacterial load and its association with otitis media.
  3. BMC Infect Dis. 2013;13:312. Dunne et al. Detection of group a streptococcal pharyngitis by quantitative PCR.