Comparing the Ecological Niches of Chlamydial and Gonococcal Infections in Winnipeg, Canada: 2007-2016.

BACKGROUND: Previous studies have shown substantial differences in geographic clustering of sexually transmitted infections (STI), such as chlamydia (CT) and gonorrhea (NG), conditional on epidemic phase. Chlamydia and NG have recently shown resurgent epidemiology in the northern hemisphere. This study describes the recent epidemiology of CT and NG in Winnipeg, Canada, combining traditional surveillance tools with place-based analyses, and comparing the ecological niches of CT and NG, in the context of their evolving epidemiology. METHODS: Data were collected as part of routine public health surveillance between 2007 and 2016. Secular trends for CT and NG, and CT/NG coinfection were examined. Gini coefficients and population attributable fractions explored the distribution, and concentration of infections over time and space. RESULTS: Rates of CT increased from 394.9/100,000 population to 476.2/100,000 population from 2007 to 2016. Gonorrhea rates increased from 78.0/100,000 population to 143.5/100,000 population during the same period. Each pathogen had its own ecological niche: CT was widespread geographically and socio-demographically, while NG was clustered in Winnipeg's inner-core. CT/NG co-infections had the narrowest space and age distribution. NG was shown to be undergoing a growth phase, with clear signs of geographic dispersion. The expansion of NG resembled the geographic distribution of CT. CONCLUSIONS: We demonstrated that NG was experiencing a growth phase, confirming theoretical predictions of geographic dispersion during a growth phase. During this phase, NG occupied similar geographic spaces as CT. Knowledge of different ecological niches could lead to better targeting of resources for subpopulations vulnerable to STIs.

Can enhanced screening of men with a history of prior syphilis infection stem the epidemic in men who have sex with men? A mathematical modelling study.

OBJECTIVES: The aim of this study is to determine the transmission impact of using prior syphilis infection to guide a focused syphilis screening intervention among men who have sex with men (MSM). METHODS: We parameterised a deterministic model of syphilis transmission in MSM to reflect the 2011-2015 syphilis outbreak in Winnipeg, Canada. Enhanced screening of 75% of men with prior syphilis every 3 months (A) was compared with distributing equivalent number tests to all MSM (B) or those with the highest partner number (C). We compared early syphilis incidence, diagnoses and prevalence after 10 years, relative to a base case of 30% of MSM screened annually. RESULTS: Strategy A was expected to avert 52% of incident infections, 44% of diagnosed cases and reduce early syphilis prevalence by 89%. Strategy B had the least impact. Strategy C was most effective, averting 59% of incident cases. When screening frequency was semiannual or annual, strategy A was the most effective. CONCLUSIONS: Enhanced screening of MSM with prior syphilis may efficiently reduce transmission, especially when identification of high-risk men via self-reported partner numbers or high-frequency screening is difficult to achieve.

Epidemiology of incident chlamydia and gonorrhoea infections and population attributable fractions associated with living in the inner-core of Winnipeg, Canada.

Population attributable fractions help to convey public health significance of differential disease risk for chlamydia and gonorrhoea. Geographical residence serves as a useful proxy for complex processes creating ill health. Using population-based data, Poisson regression models were used to examine factors associated with chlamydia and gonorrhoea incidence. Population attributable fractions due to residency in the Winnipeg Health Region's inner-core were determined for chlamydia/gonorrhoea infections among 15-59-year olds (2005-2013), stratified by age group. For both chlamydia and gonorrhoea, it was found that the 15-24-year old age group had the highest incidence rates. There was also a stronger association between residency in the inner-core and incidence for gonorrhoea, compared to chlamydia. Overall, 24% (95% CI: 12-34%) of chlamydia infections were attributable to residency in the inner-core, compared to 46% (95% CI: 35-54%) for gonorrhoea ( p < .05). Within chlamydia/gonorrhoea, no statistically significant differences in population attributable fraction were observed by age group. The conclusion was that a concentration of efforts towards inner-core residents with gonorrhoea infections may result in a relatively larger decrease in incidence.