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Abstract
Background Recent increases in bacterial STI in Canada and the resurgence of syphilis require further investigations into the transmission of STI. Specifically, adaptation of sexual networks and sexually transmitted pathogens to prevention efforts such as screening and partner notification have been proposed as a major factor in persistence of STI. We investigate the size and morphology of sexual networks generated by routinely collected contact tracing data for gonorrhoea, chlamydia and syphilis for the whole province of Manitoba, at three time points; 1990–1992; 1997–1998, and last, from 2002 to 2003.
Methods We compared the sizes of the components in which cases and contacts were connected by sexual intercourse at the three time points, and cross matched chart numbers of the cases from 1990–1992 with those from 1997–1998 in order to identify which individuals were active within specific networks 8–10 years later. We reviewed the changes in the networks along with the rates over time in order to assess the epidemic phases of the pathogen and their possible effects on the networks.
Results From 1990 to 1992, 20 223 cases were available for analysis; from a 6-month period in 1997–1998, 4544 cases and contacts were available, and last for 2002–2003; 8746 cases and contacts were available over 2 years. For the first 3-year period, components ranged from 1 to 2166; in 1997–1998; from 1 to 82 people, and from 1 to 33 people in 2002–2003. The giant component decreased by an order of magnitude over time as a proportion of all components, consisting of 9.4% of the population in the first time period, 1.8% in the second, and 0.4% (Abstract P1-S5.37 figure 1). Twenty people who had chlamydia or gonorrhoea in 1990–1992 had subsequent STIs every 2–3 years up to an including 1997–1998. They were significantly younger than other cases, (means 17.81, 23.27, p=0.0002) and were more likely to be of North American Indian ancestry (OR14.22, p<0.0001). They did not differ by area of residence or gender and the sizes of the components in which all cases and contacts were connected by sexual intercourse in 1997/98 were similar to those in which the 20 long term repeaters were active.
Evolution of sexual networks over time in Manitoba, Canada A) Pruned largest component, n=2, 166, 1990–1992, B) Largest component n=82, 1997–1998 and C) largest component n=33, 2003–2004.
Conclusions The existence of 20 young, First Nations people who had STI at least every 2–3 years from 1990–1998 provides evidence that the STD core group likely consists of some of the same people over a 7–9-year period, who by virtue of their repeated infections contribute disproportionately to STI transmission. The decrease in size of the large components together with decreases in STI supports the hypothesis that eco-niches of STI adapt to control programs over time.