Using whole genome sequencing to investigate tuberculosis outbreaks in a large UK city: examining the effectiveness of a stone in pond contact tracing approach

Abstract

Background: Mycobacterium tuberculosis is a respiratory droplet spread bacterial disease. Exposure can result in a latent state with subsequent active infection. Contact tracing aims to identify these susceptible contacts. The long-term effectiveness of the conventional approach (stone in pond model) is assessed using whole genome (WGS) sequencing to link cases retrospectively.

Methods: Through a retrospective descriptive analysis, we compare contacts identified contemporaneously with whole genome sequenced clusters. This utilises public health data from a large UK urban population as part of active case investigations in non-household settings.

Results: Over 7 years, 167 incidents were investigated with 9 outbreaks events occuring. Thirty-five active cases generated 2511 contacts from contemporaneous contact tracing investigations. Retrospective analysis demonstrated that WGS cluster sizes exceeded contemporaneous contact tracing populations with clusters continuing to grow after epidemiologically completed contact tracing events.

Conclusion: The WGS cluster sizes demonstrate missed active cases when compared to the contemporaneously identified contact tracing population. The stone in pond approach to contact tracing may not represent the optimal strategy.