Chlamydia trachomatis Infection in Female Partners of Circumcised and Uncircumcised Adult Men

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1 American Journal of Epidemiology Advance Access published September 21, 2005 American Journal of Epidemiology Copyright ª 2005 by the Johns Hopkins Bloomberg School of Public Health All rights reserved; printed in U.S.A. Vol. 162, No. 9 DOI: /aje/kwi284 Original Contribution Chlamydia trachomatis Infection in Female Partners of Circumcised and Uncircumcised Adult Men Xavier Castellsagué 1, Rosanna W. Peeling 2, Silvia Franceschi 3, Silvia de Sanjosé 1, Jennifer S. Smith 4, Ginesa Albero 1, Mireia Díaz 1, Rolando Herrero 5, Nubia Muñoz 1, and F. Xavier Bosch 1 for the IARC Multicenter Cervical Cancer Study Group 1 Cancer Epidemiology and Registration Unit, Institut d Investigació Biomèdica de Bellvitge (IDIBELL), Institut Català d Oncologia, L Hospitalet de Llobregat, Barcelona, Spain. 2 National Laboratory for Sexually Transmitted Diseases, Health Canada, Winnipeg, Canada. 3 Epidemiology and Biology Cluster, International Agency for Research on Cancer, Lyon, France. 4 Department of Epidemiology, University of North Carolina, Chapel Hill, NC. 5 Instituto Costarricense de Investigación y Enseñanza en Nutrición y Salud (INCIENSA), San José, Costa Rica. Received for publication February 13, 2005; accepted for publication May 25, Male circumcision has been shown to reduce the risk of acquiring and transmitting a number of venereal infections. However, little is known about the association between male circumcision and the risk of Chlamydia trachomatis infection in the female partner. The authors pooled data on 305 adult couples enrolled as controls in one of five case-control studies of invasive cervical cancer conducted in Thailand, the Philippines, Brazil, Colombia, and Spain between 1985 and Women provided blood samples for C. trachomatis and Chlamydia pneumoniae antibody detection; a type-specific microfluorescence assay was used. Multivariate odds ratios were computed for the association between male circumcision status and chlamydial seropositivity in women. Compared with women with uncircumcised partners, those with circumcised partners had a 5.6-fold reduced risk of testing seropositive for C. trachomatis (82 reduction; odds ratio ¼ 0.18, 95 confidence interval: 0.05, 0.58). The inverse association was also observed after restricting the analysis to monogamous women and their only male partners (odds ratio ¼ 0.21, 95 confidence interval: 0.06, 0.72). In contrast, seropositivity to C. pneumoniae, a non-sexually-transmitted infection, was not significantly related to circumcision status of the male partner. These findings suggest that male circumcision could reduce the risk of C. trachomatis infection in female sexual partners. Chlamydia pneumoniae; Chlamydia trachomatis; circumcision; men; sexual behavior; sexually transmitted diseases Abbreviations: CI, confidence interval; HPV, human papillomavirus; MIF, microimmunofluorescence; OR, odds ratio. Chlamydia trachomatis are obligate intracellular bacteria that infect genital and ocular tissue. Chlamydial infections and their complications are costly and present a significant public health problem in both developed and developing countries. The World Health Organization estimates that approximately 92 million new cases of genital chlamydial infection occur worldwide annually. C. trachomatis is the most common bacterial cause of sexually transmitted Reprint requests to Dr. Xavier Castellsagué, Cancer Epidemiology and Registration Unit, Institut d Investigació Biomèdica de Bellvitge (IDIBELL), Institut Català d Oncologia, Gran via s/n, km 2.7, E L Hospitalet de Llobregat, Barcelona, Spain ( xcastellsague@ico.scs.es). 1

2 2 Castellsagué et al. infections in the United States, responsible for an estimated 3 million new infections each year and a total annual cost of $2 billion for care (1). Clinical manifestations of C. trachomatis infections in women include acute urethral syndrome, urethritis, bartholinitis, cervicitis, upper genital tract infection, perihepatitis, and reactive arthritis (1). Genital C. trachomatis infections have been clinically associated with cytologic cervical atypia and induction of cervical metaplasia (2), and they have been considered a likely human papillomavirus (HPV) cofactor that increases the risk of cervical cancer (3, 4). Untreated chlamydial infection can lead to severe reproductive complications being an important causal agent in pelvic inflammatory disease that can lead to infertility, ectopic pregnancy, and chronic pelvic pain (5). In men, the most common clinical manifestation is nongonococcal urethritis, causing approximately percent of all cases of nongonococcal urethritis in heterosexual men. Other clinical syndromes in men include acute epididymitis, acute proctitis, acute proctocolitis, conjunctivitis, and Reiter s syndrome (1). Male infertility, chronic prostatitis, and urethral strictures are possible results of infection. Infection with C. trachomatis is also believed to be a cofactor for transmission of human immunodeficiency virus in both men and women (6). Evidence from several studies suggests that male circumcision may reduce the risk of acquiring and transmitting a number of venereal diseases, including human immunodeficiency virus (7, 8). However, the few reports looking at the association between male circumcision and C. trachomatis infections in men have yielded inconsistent results (9 15). To our knowledge, the possible relation between male circumcision and C. trachomatis infection in the female partner has never been explored. We previously reported on a negative association between male circumcision and penile HPV DNA detection and, in men with multiple female sexual partners, on a reduced risk of developing cervical cancer in their spouses (16). In this report, we analyze data from a subset of couples who participated as controls in an international multicenter case-control study of invasive cervical cancer (17 27). The aim of this study was to explore the association between circumcision status and the risk of C. trachomatis infection in female sexual partners as assessed by type-specific serologic assays, using as a validity control serodetection of antibodies against Chlamydia pneumoniae, a non-sexually-transmitted infection. MATERIALS AND METHODS Study design Study subjects for these analyses were the controls enrolled in an international, multicenter case-control study of invasive cervical cancer conducted in Colombia (23, 25), Spain (18), Brazil (21), Thailand (20), and the Philippines (26) between 1985 and The study was coordinated by the International Agency for Research on Cancer. Each study used a similar protocol and questionnaire for recruitment and data collection. Details of the methods of each study have been published previously (16 27). In brief, women controls for the case-control studies were recruited from the general population in Spain and Colombia and from the same hospitals as the women cases for the other studies. In all studies, women controls were frequency matched to the cases with invasive cervical cancer according to age. Men eligible for the present study were the husbands or stable partners of the women controls enrolled in each of the case-control studies. A man was considered a stable partner of an enrolled woman if he reported having had regular sexual intercourse with the woman for at least 6 months, whether or not they were married or lived together. Selection of the final study couples included in this analysis was driven by the availability of sera and of information on circumcision status. All protocols were approved by the International Agency for Research on Cancer and the local ethics and research committees. Informed consent was obtained from all study subjects. Human experimentation guidelines of the International Agency for Research on Cancer and those of the participating institutions in Colombia, Spain, Brazil, the Philippines, and Thailand were rigorously followed. Questionnaire and medical examination Subjects were interviewed and information was collected on demographic and socioeconomic variables, sexual history, and circumcision status by use of a standardized questionnaire. As reported previously, self-reported circumcision status was assessed by a clinician for 97.4 percent of the men recruited in the studies in Brazil, Thailand, and the Philippines (16). Since the reliability between the two measures was very high (kappa ¼ 0.89), self-reported circumcision status was used for the current analyses. Detection of C. trachomatis antibodies The strategy used for Chlamydia antibody detection in women was identical to that used in two previous reports of the same study population (3, 4). Briefly, C. trachomatis immunoglobulin G antibodies were determined by a microimmunofluorescence (MIF) assay (28), considered the reference standard for chlamydial serology. MIF assays were conducted blinded to the partner s circumcision status. The antigen panel consisted of purified elementary bodies of C. trachomatis (serovar A and three pooled serovar groups of BDE, CJHI, and FGK) and C. pneumoniae, which was included to monitor cross-reactive, genus-specific antibody responses against all chlamydial species. Sera were screened for C. trachomatis at 1:8 dilution and titered to endpoint (1:8, 1:32, 1:128, >1:128). An immunoglobulin G titer of 1:8 against any C. trachomatis serovar group was considered evidence of past C. trachomatis infection. An immunoglobulin G titer of 1:16 against C. pneumoniae was considered evidence of past C. pneumoniae respiratory infections. As reported previously, from the biologic bank of the international study, sera with identical titers for all C. trachomatis and C. pneumoniae species were also tested

3 Male Circumcision and Female Chlamydial Infections 3 against Chlamydia psittaci (avian strain 6BC) to determine the presence of genus-specific antibody responses (3, 4). Sera from six cases and 11 controls with identical titers for C. trachomatis, C. pneumoniae, and C. psittaci, and from 20 cases and 23 controls who were seropositive for serovar A and negative for all other C. trachomatis serovars, were considered noninformative as to C. trachomatis serologic status and were not included in the analyses. Sera from subjects in Spain and Colombia that had already been evaluated by using a simplified MIF assay based on the L2 serovar were retested by using the MIF assay described above to improve the specificity of previous findings. Furthermore, a blinded reproducibility study based on the overall study sera was conducted by retesting a random sample of 222 specimens (9.5 percent) twice (4). Percent agreement for C. trachomatis serovars A, BDE, CJHI, and FGK and for C. pneumoniae was 85.3 percent, 86.2 percent, 86.7 percent, and 84.9 percent, and 89.3 percent, respectively. Statistical analyses Unconditional logistic regression models were fitted to individual data. Associations between male circumcision and chlamydia seropositivity were estimated by using multivariate odds ratios and their corresponding 95 percent confidence intervals. Unless otherwise specified in this report, all models were adjusted for study, man s and woman s age, and man s and woman s lifetime number of sexual partners. Stratified analyses were performed to assess the consistency of results across strata of other key variables, including condom use and cervical HPV DNA status as determined by polymerase chain reaction based assays, as described previously (29, 30). We assessed whether the association of circumcision status with woman s C. trachomatis seropositivity differed significantly according to the country in which the various studies were conducted. We did so by testing in the fully adjusted logistic regression model for an interaction term combining country and circumcision status. To rule out the possibility that potential associations between the partner s circumcision status and female chlamydial serostatus were not due to the potential contribution of other previous sexual partners, we performed further analyses restricted to monogamous women and their only male partner. Monogamy was self-reported and was defined as including only those women declaring in the interview that they had had one and only one lifetime sexual partner (n ¼ 253). For all analyses, a two-sided p value of less than 0.05 was considered to indicate statistical significance. RESULTS Study subjects Of the 1,382 women controls enrolled in one of the five case-control studies of invasive cervical cancer, 1,029 reported having a husband or stable male partner at study entry. A total of 589 of these women (57.2 percent) agreed to participate and were interviewed. Of those, 493 (83.7 percent) provided sera, and 300 (60.9 percent) and 305 (61.9 percent) of the samples were adequately tested for C. trachomatis and C. pneumoniae serology, respectively. Overall, women controls whose chlamydial serology status could be confirmed (n ¼ 305) were similar to the women whose chlamydial serology status could not be established (n ¼ 284) with respect to age, level of education, circumcision status, cervical HPV DNA status, and variables related to sexual behavior of the couple such as age at first sexual intercourse and lifetime number of sexual partners (data not shown). The overall prevalence of circumcision was 37.0 percent: 1.8 in Spain, 6.9 in Colombia, 7.4 in Brazil, 13.3 in Thailand, and 92.5 percent in the Philippines. Compared with uncircumcised men, circumcised men were younger and more likely to have a history of multiple sexual partners. No differences were noted with regard to other sexualbehavior characteristics such as age at first sexual intercourse, ever contact with prostitutes, genital hygiene, condom use, partner s age at first sexual intercourse, or partner s lifetime number of sexual partners (data not shown). Table 1 summarizes subjects characteristics according to C. trachomatis serostatus. The overall prevalence of female C. trachomatis was 28.0 percent: 16.7 in Brazil, 22.4 in the Philippines, 32.1 in Spain, 35.6 in Thailand, and 55.2 in Colombia. Compared with seronegative women, seropositive women were more likely to have had two or more sexual partners, be younger at first sexual intercourse, and have a current male partner with a history of multiple sexual partners. Male circumcision and female C. trachomatis seropositivity C. trachomatis seroprevalence was lower in women whose partners were circumcised than in women whose partners were not (figure 1). Moreover, in female partners of both circumcised and uncircumcised men, C. trachomatis seropositivity increased significantly with increasing number of sexual partners that the women had had and with increasing number of sexual partners that the men had had. In contrast, C. pneumoniae seropositivity was not significantly associated with any of these sexual-behavior indicators. Table 2 shows the multivariate odds ratios for the association between male circumcision and woman s C. trachomatis seropositivity, overall and by selected characteristics of women and their male partners. Male circumcision was strongly associated with a decrease in the risk of C. trachomatis seropositivity in female partners (odds ratio (OR) ¼ 0.18, 95 percent confidence interval (CI): 0.05, 0.58; p ¼ 0.004). Although data were scarce in Spain, Colombia, and Brazil, there was no evidence of heterogeneity of the associations with respect to study location (p ¼ 0.99). The inverse association was not substantially influenced by any of the assessed characteristics of the women or of the men except for condom use, for which the inverse association was observed among non-condom-users only. The risk reduction for C. trachomatis seropositivity linked to male

4 4 Castellsagué et al. TABLE 1. Female Chlamydia trachomatis seroprevalence by subjects characteristics and odds ratios for female seropositivity, Colombia, Spain, Brazil, Thailand, and the Philippines, Subjects characteristics C. trachomatis seropositivity positive Adjusted OR*,y 95 CI* All women 84/ Study location Thailand 16/ Philippines 24/ Brazil 11/ Colombia 16/ Spain 17/ Educational level attained Secondary or higher 25/ Reference None or primary 59/ , 3.25 Unknown 0/1 Age group (years) 36 17/ Reference / , / , 2.80 Lifetime no. of sexual partners 1 62/ Reference 2 22/ z 1.32, 5.64 Age at first sexual 18 62/ Reference 17 22/ z 1.10, 5.15 Condom use No 71/ Reference Yes 13/ , 3.16 Partner s age group (years) 37 14/ Reference / , / , / , 2.68 Table continues circumcision was particularly strong among older women (OR ¼ 0.07, 95 percent CI: 0.01, 0.45), women with older male partners (OR ¼ 0.11, 95 percent CI: 0.01, 0.93), and women whose male partners reported having six or more lifetime female sexual partners (OR ¼ 0.10, 95 percent CI: 0.01, 0.82; p ¼ 0.03). After we excluded couples from Brazil, Colombia, and Spain, the summary odds ratio was 0.27 (95 percent CI: 0.07, 1.04), and the summary odds ratio after excluding couples from only the Philippines was 0.11 (95 percent CI: 0.01, 0.91). Further adjustment by socioeconomic indicators and/or condom use did not substantially alter the magnitude of the above associations (data not shown). In contrast, none of the odds ratio estimates for the association between circumcision and C. pneumoniae seropositivity in the female partner was statistically significant (table 3). DISCUSSION This study shows that adult women with current circumcised partners are less likely than women with uncircumcised partners to be seropositive for C. trachomatis antibodies. Male circumcision was associated with an overall 82 percent reduction in the risk of C. trachomatis infection in their

5 Male Circumcision and Female Chlamydial Infections 5 TABLE 1. Continued Subjects characteristics C. trachomatis seropositivity positive Adjusted ORy 95 CI Partner s lifetime no. of sexual partners 1 10/ Reference / , / , / z 1.10, 6.10 Unknown 0/4 Partner s age at first sexual 17 57/ Reference 16 27/ , 3.27 Partner s ever contacts with prostitutes Never 29/ Reference Ever 55/ , 2.40 Unknown 0/2 Partner s no. of sexual partners as prostitutes 0 29/ Reference / , / z 1.06, 4.48 Unknown 0/3 Partner s condom use with regular partner{ Yes 9/ Reference No 42/ , 2.75 Partner s circumcision status Uncircumcised 62/ Reference Circumcised 22/ z 0.06, 0.63 * OR, odds ratio; CI, confidence interval. y Adjusted by study location, age, lifetime number of sexual partners, partner s age, and partner s lifetime number of sexual partners. z Statistically significant. This model was not adjusted by partner s lifetime number of sexual partners. { Excludes subjects from Spain and Colombia. female partners as assessed by type-specific serologic assays after taking into account the lifetime number of sexual partners of the couple. The inverse association was consistently found in all countries considered, although estimates were far from precise in Spain, Colombia, and Brazil. The strongest protective effect was found in older women (OR ¼ 0.07), in women with older male partners (OR ¼ 0.11), and in women whose current stable partners reported multiple (six or more) lifetime sexual partners (OR ¼ 0.10). In contrast, younger women and women with a history of consistent condom use were part of the only two subgroups of couples in which circumcision was not associated with reduced C. trachomatis serodetection. Our study thus supports the possibility that, as reported for other sexually transmitted infections, male circumcision reduces the risk of transmitting C. trachomatis to the female partner. The validity of our results is supported by the use of a multicenter study with a fair sample size of couples for whom questionnaire and serologic data were complete, a common protocol, and standardized laboratory procedures to ascertain type-specific serum antibodies against C. trachomatis. The specificity of the observed MIF antibody responses was validated by the observation that C. trachomatis antibody responses, unlike those for C. pneumoniae, were clearly correlated with indicators of sexual behavior (figure 1). Furthermore, no associations were found between male

6 6 Castellsagué et al Chlamydia trachomatis p for trend = p for trend = Lifetime number of sexual partners Uncircumcised partner Partner s lifetime number of sexual partners Circumcised partner Chlamydia pneumoniae p for trend = p for trend = Lifetime number of sexual partners Uncircumcised partner Partner s lifetime number of sexual partners Circumcised partner FIGURE 1. Female Chlamydia trachomatis (top panel) and Chlamydia pneumoniae (bottom panel) seroprevalence by partner s circumcision status and number of sexual partners, Colombia, Spain, Brazil, Thailand, and the Philippines, circumcision and past exposure to C. pneumoniae, a nonsexually-transmitted infection, neither overall nor by any of the explored characteristics of the couples (table 3). Little reliable data are available on the natural history of C. trachomatis antibody profiles during persistent or acute infections. The stability of antibody response to a single chlamydial infection over time is difficult to study because of the asymptomatic nature of the infection and hence the difficulty in controlling for whether or how often a person has been reinfected. Although C. trachomatis antibodies have been shown to persist for years, a loss of or a decrease in immunoglobulin G antibody titers may occur over time (31, 32), particularly if there is no continued antigenic stimulation (33). Nevertheless, detection of type-specific C. trachomatis antibodies is generally accepted as a measure of lifetime exposure. To our knowledge, no studies have explored at the biologic level the mechanisms by which removal of the foreskin may reduce the risk of transmitting C. trachomatis to the partner. We speculate that a penis with a prepuce is perhaps more likely to retain infected cervicovaginal secretions for a longer duration than a penis with no prepuce, subsequently increasing the likelihood of infection to the penile urethra and transmission to the vagina during intercourse. Our study has a number of limitations that should be considered in interpreting our findings. Since cervical samples were not available because they were used for HPV testing, we could not measure current C. trachomatis infection, a piece of information that could bolster the biologic plausibility of the association. However, to explore our study hypothesis, it is more adequate and informative to measure a woman s cumulative past exposure than just current infection. A possible consequence of using chlamydial serology as a marker of past exposure is that any given woman could have acquired a previous chlamydial infection from a sexual partner other than the one included in the study. However, analyses restricted to women reporting one lifetime sexual partner also yielded an inverse and statistically significant association (OR ¼ 0.21; table 2). It should be noted that the inverse association we found between male circumcision and serodetection of C. trachomatis antibodies in female partners is at best indirect because 1) we did not ascertain chlamydial serum antibodies in the men themselves, and 2) we measured through serology the woman s lifetime exposure to chlamydial infections but used the circumcision status of the current partner. However, the lack of association that we found with C. pneumoniae antibodies is consistent with the modes of transmission of these two infections, bolstering the overall biologic plausibility of the protective effect and the validity of the study. Even if we had determined serum antibodies in men and had not found an inverse association between circumcision status and the man s seroprevalence, our findings for women

7 Male Circumcision and Female Chlamydial Infections 7 TABLE 2. Odds ratios for the association between male circumcision and female Chlamydia trachomatis seropositivity by selected subjects characteristics, Colombia, Spain, Brazil, Thailand, and the Philippines, * Subjects characteristics No. Women with uncircumcised partners C. trachomatis seropositivity seropositive Women with circumcised partners seropositive Adjusted ORy 95 CIy All women / / z 0.05, 0.58 Study location Thailand 45 15/ / , 2.99 Philippines 107 3/ / , 1.21 Brazil 66 11/ /5 0 Colombia 29 16/ /2 0 Spain 53 17/ /1 0 Age group (years) / / , / / , / / z 0.01, 0.45 Lifetime no. of sexual partners / / z 0.06, / / , 2.10 Age at first sexual / / z 0.05, / / , 4.15 Cervical HPVy DNA status{ Negative / / z 0.05, 0.58 Positive 43 10/ / , 2.96 Chlamydia pneumoniae serostatus Negative 98 24/ / , 1.29 Positive / / , 1.08 Consistent condom use No / / z 0.05, 0.60 Yes 40 10/ / , 7.25 Partner s age group (years) / / , / / z 0.03, / / z 0.01, 0.93 Partner s lifetime no. of sexual partners / / , / / z 0.01, 0.82 Partner s ever contacts with prostitutes# Never / / , 1.08 Ever / / z 0.03, 0.90 Partner s age at first sexual / / z 0.06, / / , 1.42 Partner s genital hygiene as assessed by a physician** Good / / , 1.53 Poor/medium 70 15/ / , 13.1 * Reference category for all odds ratios: seronegative women with uncircumcised partners. Models were adjusted by study, man s and woman s ages, and man s and woman s lifetime numbers of sexual partners. Totals may not add up correctly because of missing values (refer to table 1). y OR, odds ratio; CI, confidence interval; HPV, human papillomavirus. z Statistically significant. This model was not adjusted by study. { These models were not adjusted by lifetime number of sexual partners. # These models were not adjusted by partner s lifetime number of sexual partners. ** Excludes subjects from Spain and Colombia.

8 8 Castellsagué et al. TABLE 3. Odds ratios for the association between male circumcision and female Chlamydia pneumoniae seropositivity by selected subjects characteristics, Colombia, Spain, Brazil, Thailand, and the Philippines, * Subjects characteristics No. Women with uncircumcised partners C. pneumoniae seropositivity seropositive Women with circumcised partners seropositive Adjusted ORy 95 CIy All women / / , 1.94 Age group (years) / / , / / , / / , 5.14 Lifetime no. of sexual partners / / , / / z 0.24, 6.80 Age at first sexual / / , / / , 68.3 Partner s age group (years) / / , / / , / / , 11.2 Partner s lifetime no. of sexual partners / / , / / , 2.07 Partner s ever contacts with prostitutes Never / / , 2.45 Ever / / , 3.28 Partner s age at first sexual / / , / / , 3.84 * Reference category for all odds ratios: seronegative women with uncircumcised partners. Models were adjusted by study, man s and woman s ages, and man s and woman s lifetime numbers of sexual partners. Totals may not add up correctly because of missing values (refer to table 1). y OR, odds ratio; CI, confidence interval. z This model was not adjusted by study. These models were not adjusted by partner s lifetime number of sexual partners. would not be necessarily inconsistent; it is possible that male circumcision reduces the risk of transmission of the infection to the partner without reducing the risk of developing an active infection in the man himself. The fact that we could not determine chlamydial serostatus in 284 women of the 589 enrolled in the entire study might have biased our results. However, it is unlikely that male circumcision or chlamydial serostatus is related to sera availability or test adequacy. To statistically assess any evidence of selection bias, we compared subjects characteristics according to whether they had contributed a valid serologic result, and we found no statistically relevant differences between the two groups. We conclude that it is likely that the only impact of not having tested this subgroup of women concerns reduced statistical precision but not selection bias. Concerning the former, the study achieved sufficient precision not only to detect in a statistically significant manner the hypothesized inverse association but also to rule out a small effect, because the upper limit of the confidence interval of the odds ratio estimate was Finally, our results may be driven by the large contribution of circumcised men from the study in the Philippines. It is possible that the observed associations were mediated by other practices or characteristics of the recruited couples in

9 Male Circumcision and Female Chlamydial Infections 9 the Philippines that we were not able to identify or quantify. However, it is reassuring that the direction and statistical significance of the overall association remained virtually unchanged after we excluded the couples from the Philippines (OR ¼ 0.11, 95 percent CI: 0.01, 0.91). We have previously shown that male circumcision may reduce the risk of penile HPV, cervical HPV, and, in women with promiscuous partners, the risk of invasive cervical cancer (16, 34). However, one potential limitation of that study was that circumcision might be related to HPV underdetection because of inadequate penile samples from circumcised men. Since circumcision status can affect neither the availability nor the adequacy of the sera being tested for chlamydial serology, our current results further strengthen our previous findings on HPV and cervical cancer. The consistency of our results for four sexually transmitted diseases (penile HPV, cervical HPV, cervical cancer, and C. trachomatis) found in the same study provides strong support for the idea that male circumcision may indeed reduce the risk of acquisition and/or transmission of a number of sexually transmitted infections. In conclusion, this study suggests that male circumcision reduces the risk of transmission of C. trachomatis to the female partner as determined by serology. Given that C. trachomatis is the most common bacterial sexually transmitted infection both worldwide (35) and in the United States (36), further data from other studies and populations using additional markers of chlamydial infection are needed to confirm this first known epidemiologic report on this inverse association and to assess potential public health implications of these findings. ACKNOWLEDGMENTS This investigation was supported by the European Community (CI F(CD)); The Fondo de Investigaciones Sanitarias (FIS), Spain (86/753, 87/1513, 88/2049, 90/0901, 95/0955, 01/1236, and 01/1237); the International Agency for Research on Cancer, Lyon, France (FI/92/3-2 PAR); Programa Interministerial de Investigación y Desarrollo, Spain (SAF 96/0323); The Rockefeller Foundation (PS 9824); and the Department of Reproductive Health and Research at the World Health Organization (grant ). Each of the authors contributed to this report in the following ways. Dr. Xavier Castellsagué envisioned the hypothesis, initiated and coordinated the analysis, and wrote the manuscript. Dr. Rosanna W. Peeling was in charge of the chlamydial serologic assays and the writing of the serologic methods section, and she made substantial contributions in interpreting and discussing the results and in writing and obtaining final approval of the manuscript. Dr. Jennifer S. Smith contributed in obtaining funding to perform serologic assays, in the discussion of the results, and in the writing of the manuscript. Dr. Silvia de Sanjosé contributed in the interpretation and discussion of results, in the coordination of several of the case-control studies, and in the writing of the manuscript. Drs. Silvia Franceschi, Rolando Herrero, Nubia Muñoz, and F. Xavier Bosch were the principal investigators of one or several of the included studies. They developed the protocols, obtained funding for fieldwork and testing of biologic samples, supervised analyses, and contributed toward revision and final approval of the manuscript. Ginesa Albero and Mireia Díaz performed data management tasks, carried out most statistical analyses, produced tables and graphs, and contributed in the interpretation and discussion of the results. All authors had full access to all study data and had final responsibility for submitting the manuscript for publication. The authors are indebted to the gynecologists, pathologists, and oncologists who helped identify the participants and facilitated their contributions and to the fieldwork supervisors. They thank L. Dillon for the MIF C. trachomatis serologic laboratory work and F. Odefrey and Y. Guy for handling the serum specimens. The IARC Multicenter Cervical Cancer Study Group is composed of the following additional researchers: Dr. M. Plummer (International Agency for Research on Cancer, Lyon), France; Drs. V. Moreno (Institut Català d Oncologia, Barcelona), L. C. González (Servicio Territorial de Sanidad y Bienestar Social, Salamanca), M. Gili (Universidad de Sevilla, Sevilla), I. Izarzugaza (Euskadi Cancer Registry, Vitoria-Gasteiz), P. Viladiu (Registre de Càncer de Catalunya, Barcelona), C. Navarro (Consejería de Sanidad, Murcia), A. Vergara (Servicio Provincial de Sanidad, Zaragoza), N. Ascunce (Programa de Cáncer de Mama, Pamplona), and M. 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