Gonorrhoea and chlamydia are curable, bacterial, sexually transmitted infections (STIs)
of humans, with important long term consequences for health. Their epidemiology and
biology are reviewed in chapter one.
The way the biology of the organisms and the behaviour of human hosts interact to
influence the patterns of infection and the potential impact of interventions is the subject
of the main body of the thesis. Mathematical models are presented, together with
empirical data, to gain a better understanding of the epidemiology of gonorrhoea and
chlamydia. New approaches are applied, using more complex measures of disease
occurrence including reinfection (subsequent infection by the same organism) or
coinfection (infection with both organisms simultaneously). Coinfection with
gonorrhoea and chlamydia is investigated in chapter two.
The third chapter investigates the importance of heterogeneity in human behaviour (i.e.
level of sexual activity, mixing patterns within and between populations) on the spread
of disease in subpopulations, using a model incorporating race, gender and sexual
activity level. This was parameterised and validated using data collected in South East
London.
In chapter four, models of reinfection are used to investigate the interaction of
population level parameters such as degree of assortative mixing and rates of
reinfection. In chapter five, the characteristics of individuals coinfected with both
organisms are shown to provide additional information useful in determining how
infection is distributed across a population.
The biology of the organism is demonstrated, in the fifth chapter, to play an important
role in the prevalence and incidence of disease within the host population. The impact
of the emergence of resistant or asymptomatic phenotypes under selective pressure by
different treatment regimens is quantified using a two strain model, including
asymptomatic and symptomatic infections. The final chapter considers the contribution
of the research and discusses the implications of the results for STI intervention strategies.