• Chlamydia trachomatis
• serovar distribution

Up to 19 different Chlamydia trachomatis (CT) serovars which are pathogenic predominantly for the urogenital tract and numerous CT variants have been identified.^1,2 An increasing number of isolates are typed worldwide and provide a wealth of information on the epidemiology of CT infections, a sexually transmitted disease (STD) for which screening has been proposed.^3–5 Recent studies have demonstrated an association between CT serovar G and squamous cell carcinoma.⁶ A possible shift in the serovar distribution over time in a region or country could reveal information on changes in the epidemiology of CT infections and could potentially have clinical implications.

We therefore determined the CT serovar distribution in a large STD population in Amsterdam in 2000–2 and compared it together with all published serovar distributions since 1986 in the Netherlands to assess if serovar distribution shifts over time occurred.

Of people attending the STD outpatient clinic in Amsterdam from 2000–2, those found CT positive (n = 407) by LCx (Abbott Laboratories, Chicago, IL, USA) were genotyped as described previously.¹ This is the largest STD population typed to date in The Netherlands. The following serovar distribution was found: B = 1%; D = 12%; Da = 0.2%; D- = 1%: E = 33%; F = 23%; G = 4%; Ga = 5%; H = 8%; I = 6%; Ia = 1%; J = 3%; K = 2%.

Literature searches identified eight serovar distribution studies in the Netherlands, of which the first was performed in 1986. With the inclusion of the present study, 2204 serovars were available for analyses. In the serovar distributions comparison, we (1) did not distinguish between male and female participants, (2) did not distinguish between serovar distributions based on serotyping or genotyping techniques, (3) excluded serovars B/Ba because of the low numbers, (4) excluded double infections, (5) excluded variants, and (6) classified CT serovars in the three phylogenetically based serogroups: the B group (serovars D, Da, D-, E), the intermediate serogroup (serovars F, G, Ga), and the C group (serovars I, Ia, J, Jv, and K).

Results are shown in figure 1. In general, no statistical significant serovar distribution trends in time were observed between 1986 and 2002 when all studies were taken together. Of the nine studies, 1 and 6 represent serovar distributions from STD populations in Rotterdam and show no significant changes in general or over time (mean: C group: 30%; Int group: 21%; B group: 49%). Studies 2, 3, 4, and 9 represent serovar distributions from STD populations in Amsterdam and show no significant changes (mean: C group: 20%; Int group: 31%; B group: 49%). Studies 5, 7, and 8 represent serovar distributions from mixed symptomatic and asymptomatic infected people (5 and 7) and asymptomatically infected populations in Amsterdam. They show no significant changes in general, over time, or compared to the Amsterdam STD based serovar distribution (C group: 17%; Int group: 30%; B group: 53%).

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Figure 1

Serovar distribution studies in the Netherlands from 1986 to 2002. The time of cohort collections is shown since the year of publication can be different from the year of cohort collection. Differences in serovar distributions in time were analysed. Each study is indicated by first author, year of publication, and number of isolates included: 1, Wagenvoort, 1998, n  =  190; 2, vd Laar, 1996, n  =  372; 3, Morré, 1998, n  =  90; 4, Ossewaarde, 1994, n  =  289; 5, Lan, 1995, n  =  51; 6, v Duynhoven, 1998, n  =  305; 7, Morré, 2000, n  =  426; Morré, 1998, n  =  74; 9, Spaargaren, this study, n  =  407. C  =  serogroup C (serovars H, I, Ia/I′, J, Jv, K); Int  =  intermediate serogroup (serovars F, G, Ga); B  =  serogroup B (serovars D, Da, D-, E).

However, when the two geographically derived serovar distributions were compared to each other, (1) serogroup C was found more frequently in Rotterdam: 30 v 19% (p<0.0001; OR 1.8 (95% CI: 1.4 to 2.3)), the most prominent serovar difference was serovar K (10.6 v 3.2%, p<0.0001; OR 3.6 (95% CI 2.4 to 5.3)); (2) the intermediate serogroup was found less frequently in Rotterdam: 21 v 31% (p = 0.0002; OR 1.6 (95% CI: 1.2 to 2.0)), the most prominent serovar difference was serovar F (15 v 22%, p = 0.0018; OR 1.6 (95% CI: 1.2 to 2.1)), and serogroup B was stable (49% v 50%).

In conclusion, no changes in serovar distribution differences were found over time in the Netherlands in general or within the two different geographic areas. However, the Rotterdam population differed significantly from the Amsterdam populations in having a larger incidence of C group serovars and a lower incidence of the intermediate group serovars, albeit an identical B group serovar distribution. The findings could be the result of different ethnic compositions of the studied cohorts or other confounding factors between Rotterdam and Amsterdam, a subject that warrants further study.