Outbreak or illusion: consequences of 'improved' diagnostics for gonorrhoea

Area of Science:

• Clinical Microbiology
• Sexual Health Diagnostics
• Public Health Surveillance

Background:

• The introduction of nucleic acid amplification testing (NAAT) for gonorrhoea using the BD Viper XTR™ System in Oxford led to a threefold increase in reported cases.
• This increase raised concerns about a potential gonorrhoea outbreak, prompting an investigation into the accuracy of the initial testing method.

Purpose of the Study:

• To evaluate the false-positive rates of gonorrhoea NAAT using the BD Viper XTR™ System.
• To assess the necessity and impact of confirmatory testing for gonorrhoea diagnoses.

Main Methods:

• A retrospective review was followed by a six-month prospective study.
• All positive gonorrhoea samples from the BD Viper XTR™ System underwent confirmatory testing on a different platform.

Main Results:

• Significant presumptive false-positive rates were identified: 27% in females, 13.2% in heterosexual males, 3.5% in multi-site MSM, and 62.8% in pharyngeal-only MSM.
• These rates highlight issues with the initial NAAT, particularly cross-reactivity with commensal Neisseria species.

Conclusions:

• The study demonstrates substantial false-positive rates for gonorrhoea NAAT with the BD Viper XTR™ System in this population.
• Confirmatory testing using a second nucleic acid target is essential, aligning with BASHH/Public Health England guidelines, especially in low-prevalence settings and for extragenital samples.