Research manager SpeeDx Pty Ltd EVELEIGH, New South Wales, Australia
BACKGORUND In general, antibiotic treatment is offered to patients who test positive for Chlamydia trachomatis (CT) and/or Neisseria gonorrhoeae (NG). However, since gold standard nucleic acids amplification tests (NAAT) are known to detect residual nucleic acids post cell death, they’re unable to distinguish viable from non-viable infections. As such, the clinical relevance of some positive results is questionable, particularly within asymptomatic populations and/or when assessing clearance post treatment. This may negatively impact public health, leading to unwarranted antibiotic consumption and increased antimicrobial resistance. Assessment of pathogen viability could counteract this. InSignia®, a novel NAAT, measures active RNA transcription associated with viable pathogens only.
METHODS InSignia amplified regions of CT and/or NG in a single tube one-step reverse transcriptase qPCR reaction using total nucleic acid extracts. Assays specifically targeted i) a gene and associated RNA transcripts and ii) a non-transcribed DNA region. Results from PCR, expressed as an Index, reflected the internal ratio of RNA normalised to DNA. This allowed detection and elucidation of viability, which was compared to results from conventional NAATs and culture respectively.
RESUTS In vitro experiments used InSignia to distinguish viable CT or NG from non-viable cells. Results showed that viability assessment, or Indexes obtained, was independent of both the target concentration and the presence of non-viable organisms. When tested on clinical specimens, the sensitivity and specificity of InSignia for pathogen detection was comparable to conventional NAATs, with > 93% concordance; however, InSignia also ascertained viability. In some instances, potential overtreatment was identified, specifically in asymptomatic individuals, with 35% lacking viable infections, when reassessed prior to commencement of treatment and on average 3-4 days after initial diagnosis. Viability assessment was more sensitive than that observed with culture.
CONCLUSION InSignia is a sensitive novel NAAT for assessment of viability of CT and NG. This test has the potential to transform the current paradigm of pathogen testing and improve patient management. The approach has application for diagnosis prior to treatment or at test-of-cure, and could be implemented within centralised labs and POC settings. Inclusion of InSignia in clinical practice could decrease antibiotic consumption and contribute to antibiotic stewardship.
