Distinct transmission networks of Chlamydia trachomatis in men who have sex with men and heterosexual adults in Amsterdam, The Netherlands

Abstract

Background: Genovar distributions of Chlamydia trachomatis based on ompA typing differ between men who have sex with men (MSM) and heterosexuals. We investigated clonal relationships using a high resolution typing method to characterize C. trachomatis types in these two risk groups.

Methods: C. trachomatis positive samples were collected at the STI outpatient clinic in Amsterdam between 2008 and 2010 and genotyped by multilocus sequence typing. Clusters were assigned using minimum spanning trees and these were combined with epidemiological data of the hosts.

Results: We typed 526 C. trachomatis positive samples: 270 from MSM and 256 from heterosexuals. Eight clusters, containing 10-128 samples were identified of which 4 consisted of samples from MSM (90%-100%), with genovars D, G, J, and L2b. The other 4 clusters consisted mainly of samples from heterosexuals (87%-100%) with genovars D, E, F, I, and J. Genetic diversity was much lower in the MSM clusters than in heterosexual clusters. Significant differences in number of sexual partners and HIV-serostatus were observed for MSM-associated clusters.

Conclusions: C. trachomatis transmission patterns among MSM and heterosexuals were largely distinct. We hypothesize that these differences are due to sexual host behavior, but bacterial factors may play a role as well.

Figure 1. Minimum spanning tree showing ompA genovar type of 526 Chlamydia trachomatis-positive samples from MSM and heterosexuals in Amsterdam between July 2008 and May 2010.

Sizes of the node discs are proportional to the number of samples of each sequence type; branches show single locus variants (SLV); halos indicate clusters based on SLV; and letters indicate ompA genovar type. The color coding is: red, genovar D (n = 115); yellow, genovar E (n = 112); black, genovar G (n = 102); green, genovar F (n = 61); blue, genovar J (n = 56); pink, genovar I (n = 31); gray, genovar L2b (n = 31); brown, genovar K (n = 11); cyan, genovar L2 (n = 3); purple, genovar B (n = 2); and orange, genovar H (n = 2).

Figure 2. Minimum spanning tree showing the sexual orientation of the host of 526 Chlamydia trachomatis-positive samples from MSM and heterosexuals in Amsterdam between July 2008 and May 2010.

Sizes of the node discs are proportional to the number of samples of each sequence type; branches show single locus variants (SLV); halos indicate clusters based on SLV; and letters indicate ompA genovar type. The color coding is: pink, men who have sex with men only (n = 262); green, men who have sex with men and women (n = 8); and blue, heterosexual men and women (n = 256).