Novel Transmission Model for Gonorrhea

This project is developing a novel mathematical model for evaluating the transmission of gonorrhea strains in heterosexual and homosexual populations in the United States.

Gonorrhea is the second most prevalent bacterial STI in the United States, with the highest prevalence observed regionally in the Southeast and in the men who have sex with men (MSM), African-American and young adult populations. Gonorrhea infection can be asymptomatic, resulting in many undetected cases in the absence of targeted screening policies. Undetected cases have an increased risk of progressing to adverse health outcomes such as pelvic inflammatory disease.

Another significant element in the current epidemiology of Gonorrhea is the development of antimicrobial resistance in many Neisseria gonorrhoea strands. Antibiotics previously used to treat infection, such as Ciprofloxacin, have now increased gonorrhea prevalence in the U.S. (Chesson et al. 2014). Transmission dynamics have been found to vary between the populations of interest, creating a need for population-specific analyses and interventions (Kirkcaldy et al. 2013) (Grad et al. 2014).

Our model will capture the essential features of gonorrhea epidemiology in the U.S. population, including antimicrobial resistance and genotyping, to assess interventions for reducing the burden of disease.

Major research questions include:

Impact and economics of interventions to reduce gonorrhea prevalence and burden:

• What is the expected trajectory of gonorrhea prevalence using current control measures?
• How do predicted impact and costs vary between strategies for testing policies targeting the general population compared to targeting at risk groups only?
• Would novel testing strategies reduce gonorrhea incidence by removing barriers to testing and delays in treatment in subgroups with high incidence?
• How can novel partner notification strategies be improved, and what level of partner treatment is needed to substantially reduce gonorrhea incidence?

Impact of interventions in relation to patterns and trends in antimicrobial resistance:

• Which treatment strategies (such as single drug therapy versus combination therapy, switching antimicrobials, retesting and re-treatment of cases) maximize benefits in terms of controlling and reducing antimicrobial-resistant gonorrhea in the population and what are the associated costs?
• Would different regions of the United States benefit from different treatment strategies given that prevalence of antimicrobial resistance is highly variable between regions and risk groups?
• Can use of second-line oral treatment regimens for expedited partner therapy potentiate spread of increased antimicrobial resistance?
• How do the predictions for antimicrobial resistance differ between heterosexual and homosexual populations, different age groups and different ethnicities, and how does this influence optimal control measures?
• What is the expected impact of an emerging gonorrhea strain with multidrug antimicrobial resistance, but associated fitness costs, on the U.S. population?

References:

1. Centers for Disease Control and Prevention, 2013. 2013 STD Surveillance Gonorrhea. Available at: http://www.cdc.gov/std/stats13/gonorrhea.htm [Accessed May 6, 2015].
2. Chesson, H.W. et al., 2012. Disparities in sexually transmitted disease rates across the “eight Americas”. Sexually transmitted diseases, 39(6), pp.458–64.
3. Grad, Y.H. et al., 2014. Genomic epidemiology of Neisseria gonorrhoeae with reduced susceptibility to cefixime in the USA: A retrospective observational study. The Lancet Infectious Diseases, 14(3), pp.220–226.
4. Kirkcaldy, R.D., Bolan, G.A. & Wasserheit, J.N., 2013. Cephalosporin-resistant gonorrhea in North America. JAMA, 309(2), pp.185–7.