Background The reported incidence rate of gonorrhoea has more than doubled between 2000 and 2010 in Montréal, increasing in both genders and all age groups; however, it was particularly high in females aged 15 to 24. As the reasons for the increases among young women are not fully understood, we wanted to determine whether neighbourhood-level population characteristics were associated with incidence rates among them, to help target intervention strategies.
Methods Incident gonorrhoea cases were female residents of Montréal, aged 15 to 24, who met Québec's provincial gonorrhoea surveillance definition, with a notification date between 2002 and 2009. The unit of analysis was neighbourhoods—111 non-administrative boundaries defined by the Montréal Public Health Department, by grouping census tracts to maximise homogeneity of population characteristics. The dependent variable was the neighbourhood gonorrhoea incidence rate based on all reported cases and the neighbourhood population, for females aged 15 to 24; the independent variables included material and social deprivation indices, their combination and components, and ethnic origin. Adjusted incidence rate ratios (IRR) were estimated by negative binomial regression after exponentiation of the regression coefficients and show the change in the incidence of gonorrhoea for each unit increase in the independent variable. In the final model, independent variables were normalised to facilitate comparison of their IRR which represents the change in gonorrhoea incidence rate associated with an increase of one SD in the percentage of residents of a given ethnic origin.
Results A total of 837 cases were reported (cumulative incidence rate 5.6 per 100 000). Higher proportions of three ethnic origin groups were associated with higher neighbourhood gonorrhoea rates, even when deprivation indices were considered (Abstract P1-S4.12 table 1).
Conclusions Customary methods for gonorrhoea surveillance consider individual characteristics of cases as risk factors for disease. However, gonorrhoea is clustered in neighbourhoods that have high proportions of African, Aboriginal and Caribbean populations. The ecological approach used in this study suggests that certain phenomena exist at the population level that may not exist at the individual level, which can be used to target population-level prevention programs.