The transmission dynamics of gonorrhoea: modelling the reported behaviour of infected patients from Newark, New Jersey

A survey of the sexual behaviour of gonorrhoea patients in Newark was under taken to evaluate parameters within a model of gonorrhoea transmission. Mod elling work aimed to explain observed epidemiological patterns and to explo re the potential impact of interventions. Reported behaviours, along with v alues derived from the literature, were used within a standard deterministi c model of gonorrhoea transmission, where the population was stratified acc ording to sex and rates of sex-partner change. The behaviours reported, par ticularly among women, are insufficient by themselves to explain the contin ued existence of gonorrhoea within the population The majority of symptomat ic patients seek treatment within a few days, and report that they do not h ave unprotected sex while symptomatic. The proportion of patients with low numbers of sex partners suggests that sexual mixing between people categori zed according to sexual behaviour is near random. To explain the persistenc e of gonorrhoea, there must be some patients who, when infected, do not see k care in public clinics. In addition, gonorrhoea incidence in the model is sensitive to change, such that very small reductions in risk behaviour cou ld lead to its elimination. This does not accord with the observed failure of many interventions to eliminate infection, suggesting that the modelled infection is too sensitive to change. The model, which has been influential in gonorrhoea epidemiology, is not consistent with the observed epidemiolo gy of gonorrhoea in populations. Alternative models need to explore the obs erved stability of gonorrhoea before robust modelling conclusions can be dr awn on how best to control infection. However, the current results do highl ight the potential importance of asymptomatic infections and infections in those who are diseased and do not attend public health services. Screening and contact-tracing to identify asymptomatic infections in both men and wom en will be more effective in reaching those who maintain the infection with in the community rather than simply treating symptomatic cases.