Modelling outbreak response strategies for preventing spread of emergent Neisseria gonorrhoeae strains in men who have sex with men in Australia
Authors: Duan Qibin , Carmody Chris , Donovan Basil , Guy Rebecca J , Hui Ben B , Kaldor John M , Lahra Monica M , Law Matthew G , Lewis David A , Maley Michael , McGregor Skye , McNulty Anna , Selvey Christine , Templeton David J , Whiley David M , Regan David G , Wood James G 
Published: May 2021

The ability to treat gonorrhoea with current first-line drugs is threatened by the global spread of extensively drug resistant (XDR) Neisseria gonorrhoeae (NG) strains. In Australia, urban transmission is high among men who have sex with men (MSM) and emergence of an imported XDR NG strain in this population could result in an epidemic that would be difficult and costly to control. An individual-based, anatomical site-specific mathematical model of NG transmission among Australian MSM was developed and used to evaluate the potential for elimination of an emergent XDR NG strain under a range of case-based and population-based test-and-treat strategies. When applied upon detection of the imported strain, these strategies enhanced the probability of elimination and reduced the outbreak size compared with current practice. The most effective strategies combined testing targeted at regular and casual partners with increased rates of population testing. However, even with the most effective strategies, outbreaks could persist for up to 2 years post-detection. Our simulations suggest that local elimination of emergent NG XDR strains can be achieved with high probability using combined case-based and population-based test-and-treat strategies. These strategies may be an effective means of preserving current treatments in the event of wider XDR NG emergence.

Author Summary

In most high-income settings, gonorrhoea transmission is endemic among men who have sex with men (MSM). While gonorrhoea remains readily treatable, there are major concerns about further resistance due to recent reports of treatment failure with first-line therapy and limited remaining treatment options. Here we investigated the potential for trace and treat response strategies to eliminate such strains before their prevalence reaches a level requiring a shift to new first line therapies. Rather than directly consider resistance, we explore the mitigating effect of various test and trace measures on outbreaks of a generic imported strain which remains treatable. This is done within a realistic mathematical model of spread in an MSM community that captures cases, anatomical sites of infection and contacts at an individual level, calibrated to Australian epidemiology. The results indicate that strategies such as partner tracing and treatment in combination with elevated asymptomatic community testing are highly effective in mitigating outbreaks but can take up to 2 years to achieve elimination. As there are currently no clear alternatives of proven efficacy and safety to replace ceftriaxone in first-line therapy, these promising results suggest potential for use of these outbreak response strategies to enable continuation of current treatment recommendations.