In this study from the large population-based Costa Rica HPV Natural History Study, we did not find an association between C trachomatis
infection and CIN2+ among subjects with carcinogenic HPV DNA at baseline. Determining the role of C trachomatis
as a cofactor for cervical premalignancy and/or invasive cancer requires that HPV status and the natural history of cervical cancer be taken into consideration. The multistage development of invasive cervical cancer from HPV infection takes many years. In general, HPV infections occur close to the age of sexual debut, more than 90% disappear within 2–5 years, and most women who are diagnosed with cervical cancer are aged 40 years or older (3,25
HPV is the most prevalent viral sexually transmitted infection, C trachomatis
is the most prevalent bacterial sexually transmitted infection, and co-infections with both are common (26
). We showed that C trachomatis
status at enrollment was a risk factor for current and subsequent carcinogenic HPV infection (RR = 2.6, 95% CI = 1.6 to 4.2). It is therefore possible that C trachomatis
is associated with cervical cancer because it is associated with HPV acquisition (either by a noncausal link through common risk factors, such as infected partners and sexual behaviors, or by a causal disruption of the epithelial tissue). However, on the basis of our results, it appears to be unlikely that C trachomatis
infection affects HPV persistence and progression to cervical premalignancy because we found no association between C trachomatis
status and CIN2+ or between C trachomatis
status and CIN3+ in our analysis after adjusting for HPV (by restricting the analysis to carcinogenic HPV-infected women).
Whether C trachomatis
acts as a cofactor in the steps from progression from premalignancy to invasive cervical cancer cannot be adequately addressed by results of this study because the study was not sufficiently powered to evaluate the role of C trachomatis
in invasive cervical cancer. The lack of association between C trachomatis
and invasive cervical cancer observed in this analysis is contrary to findings of the pooled study of case–control studies of invasive cervical cancer from International Agency for Research on Cancer (IARC) (4
). They found a positive association between C trachomatis
serology and invasive cervical cancer among HPV-positive women. The IARC study was large and had a well-designed epidemiological and laboratory component. However, the lack of prospective information for control subjects in that study means that HPV status and C trachomatis
status at relevant times were not available.
Our results also differ from other studies that found a positive association between C trachomatis
status and invasive cervical cancer, after adjusting for HPV seropositivity in a statistical model (6
) or using HPV serostatus as a marker of HPV exposure among control subjects (8
). Retrospective control for HPV by use of HPV serology is insensitive and thus not an ideal adjustment in examining a possible link between C trachomatis
and cervical cancer. Because HPV is a necessary etiologic agent for cervical cancer and thus a strong confounder, even weak associations with a positive HPV status can result in the identification of a spurious epidemiological association. Although HPV serology is thought to be a fairly specific surrogate for cumulative HPV exposure (31
), it has low sensitivity because not all HPV-infected women seroconvert. Additionally, the HPV serology tests used in some previous studies targeted only a few HPV types (7
). Hence, observed positive associations might have resulted from residual confounding caused by misclassification of HPV status.
Moreover, the observation that a positive C trachomatis status at enrollment was associated with an increased risk for subsequent carcinogenic HPV infection may explain why C trachomatis was also associated with an increased risk for CIN2+ among initially HPV-negative women. Adjustment for HPV status at enrollment eliminated the association between a positive C trachomatis status and CIN2+, perhaps because a positive C trachomatis status might be associated with an unknown or unmeasured set of behaviors or sexual partner characteristics that lead to both future and concurrent HPV infection. This consideration is important when evaluating retrospective studies that used HPV status at a single time point in their adjustment for HPV, especially among control subjects.
Two interesting observations in our study were the association between a positive C trachomatis
status and an incident CIN2+ among subjects who initially had a negative HPV status and the lack of an association among subjects who initially had a positive HPV status. These results indicate that stratum-specific analyses provided greater insight into the relationship between C trachomatis
and CIN2+. The assays that we used to determine C trachomatis
status differed from those used in previous studies (4
). Previous studies used the micro-immunofluorescent assay to determine C trachomatis
serological status; although this assay is considered to be the gold standard, it is subjective and it requires considerable experience to differentiate between strains, and labor intensive particularly for large epidemiological studies. A strength of this study was that we used two different assays to measure C trachomatis
status. 1) The serological assay that we used as a measure of past C trachomatis
exposure was very specific for C trachomatis
. 2) The C trachomatis
DNA assay examined current C trachomatis
infection at the cervix. This assay provided a novel aspect for this study. Both these assays have similar or higher sensitivity and specificity compared with other commercial assays (23
). Although we mention these differences in the assays used for completeness of discussion, we do not believe that the differences were large enough to have resulted in the discrepant finding between studies. To ensure that our measures of C trachomatis
were accurate, we examined determinants of C trachomatis
DNA and seropositivity among the control subjects and showed that C trachomatis
DNA status was independently associated with several sexual risk factors, and C trachomatis
IgG status was independently associated with ectopic pregnancy.
We constructed a model by statistically adjusting for HPV16 serology (dichotomous negative vs. positive test results, excluding equivocal test results), sexual risk factors (including lifetime number of sexual partners on a continuous scale), and enrollment age (on a continuous scale) to investigate the association between C trachomatis
(DNA and/or seropositivity, to try to increase our power), and CIN2+, to replicate previous studies (6
). We observed an increased risk of C trachomatis
infection among case subjects compared with control subjects (OR = 1.35, 95% CI = 1.01 to 1.82); however, when we restricted the analysis to HPV16-seropositive subjects (not including equivocals), we found no association (OR = 0.84, 95% CI = 0.48 to 1.48) (data not shown).
The number of subjects with specific C trachomatis
DNA serovars was too small to examine the association between each serovar and CIN2+, and so we investigated the association at the C trachomatis
serogroup level. One notable finding of this study was a non-statistically significantly increased association between the non-B serogroups and CIN2+, indicating that, if C trachomatis
is a cofactor in CIN2+, then C trachomatis
would belong to one of the non-B serogroups. These data are in concordance with the association of serovar G antibodies and squamous cell carcinoma of the cervix, as described previously (6
). The most prevalent serovars among women in Costa Rica belong to the serogroup B (specifically, serovars E and D or Da) and the intermediate serogroups (serovar F) (23
). Interestingly, we found a statistically significant protective association between serogroup B and CIN2+ among HPV-positive women. These findings were based on very few subjects and need to be validated in larger cohorts.
Our study was limited by lack of data on treatment for C trachomatis. Because this analysis was conducted after the completion of the cohort study, in which C trachomatis testing was not part of the protocol, women might have sought treatment for C trachomatis on their own. In addition, no information on treatment for other sexually transmitted infections was collected.
In summary, we found no association between C trachomatis status, as assessed by DNA or serology, and risk of cervical premalignancy after controlling for carcinogenic HPV-positive status. Thus, previous reports of an association between C trachomatis and cervical premalignancy may be, in part, caused by confounding by HPV status or by an increased susceptibility to HPV infection among women with a positive C trachomatis status.