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A Nationwide Sentinel Clinic Survey of Chlamydia trachomatis Infection in Finland

HILTUNEN-BACK, EIJA MD*†; HAIKALA, OLLI MD; KAUTIAINEN, HANNU; PAAVONEN, JORMA§AND; REUNALA, TIMO*∥

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Background Chlamydia trachomatis has been recognized as a major sexually transmitted infection in North America and Western Europe during the past two decades. The incidence of C trachomatis in Finland has been continuously high throughout the 1990s.

Objectives As the epidemic of C trachomatis infection continues in Finland, there is a need to obtain up-to-date information on the prevalence and patient profiles in the planning of preventive strategies.

Methods A nationwide sentinel clinic network consisting of seven sexually transmitted disease (STD) and five general student health clinics was established in 1995. Data were collected during a 3-year period (1995–1997) from 3,686 patients with and 32,230 patients without C trachomatis using a self-administered questionnaire.

Results The prevalence of chlamydia was 8.4% in the STD clinics and 5.3% in the general clinics; 90% of the infections were endemic. The prevalence was highest in the youngest age group (15–19 years; 16% in females, 14% in males). The patients with chlamydia were significantly younger (mean age: men 26.6 years, women 23.7 years) than those without chlamydia. Women with chlamydia used oral contraceptives or intrauterine devices (IUD) significantly more often (59%) than women without chlamydia (42%). A high number of sex partners and a history of previous chlamydia during the preceding 12 months were also risk factors. Men contracted chlamydia frequently from a casual partner (61%) but rarely from a commercial sex worker (2%). For women, the source partner was most often a regular one (61%). The median time from exposure to attendance was 34 days, and was highest when the source partner was a spouse. One third of the patients could have spread chlamydia to a new partner before the diagnosis.

Conclusions C trachomatis infection is spread all over Finland, and the risk factors include younger age, high number of sex partners, and use of oral contraceptives or IUDs. Source partner analysis focused attention on the importance of transmission from regular partners, especially in women. The time from transmission to diagnosis was long, and any effort to shorten this period would be an effective preventive strategy.

From the Departments of *Dermatology and Venereology and §Obstetrics and Gynecology, University of Helsinki and University Hospital of Helsinki, Helsinki, Finland; the †National Public Health Institute, Helsinki, Finland; the ‡Rheumatism Foundation Hospital, Heinola, Finland; and the Department of Dermatology and Venereology, University of Tampere and University Hospital of Tampere, Tampere, Finland

Supported by a grant from the Helsinki University Hospital Research Fund.

Reprint requests: E. Hiltunen-Back, MD, Department of Dermatology and Venereology, Helsinki University Central Hospital, FIN-00250 Helsinki, Finland. Email: eija.hiltunen-back@hus.fi

Received for publication May 22, 2000, revised September 13, 2000, and accepted September 14, 2000.

CHLAMYDIA TRACHOMATIS has been recognized as a major sexually transmitted infection (STI) in North America and Western Europe during the past two decades. The incidence of C trachomatis in Finland has been continuously high in the 1990s (149 to 155 per 100,000 inhabitants), though gonorrhea has almost disappeared in this area. 1 The incidence of syphilis has also remained low in Finland, despite that severe epidemics have occurred in Russia and the Baltic countries. 2,3 In addition, the incidence of HIV infection is one of the lowest in the European countries. Recent studies from the United States and European countries have focused attention on the high frequency of C trachomatis infection, especially among sexually active young adults. 4,5 It has been also shown that screening and treatment of C trachomatis infection decreases pelvic inflammatory disease and ectopic pregnancies. 6 The annual cost of C trachomatis infections to the healthcare system is enormous, and screening programs in women are cost effective in low-prevalence populations. 7

The surveillance of C trachomatis infections and other STIs in Finland is based on infectious disease legislation. Physicians and laboratories notify patients with STIs to a national register, but the data collected are limited and include only the age, gender, and geographic location of the patient. To get more detailed information regarding C trachomatis and other STIs for epidemiologic purposes, a sentinel sexually transmitted disease (STD) surveillance network was established in Finland in 1995. This network consists of 12 STD and non-STD clinics, and collects systematic epidemiologic data from patients with STIs and source partners. We report the first results from the sentinel clinic network focusing on C trachomatis infections, and especially on patient and partner profiles.

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Materials and Methods

Sentinel STD Surveillance Network

The network was planned to include several clinics caring for patients with STIs, and to cover at least 10% of all C trachomatis infections reported in Finland. 8 At the beginning of 1995, the network included five university hospital or municipal STD clinics in Helsinki, Turku, Tampere, and Oulu, two student health clinics in Helsinki and Oulu, three general healthcare clinics in Lappeenranta, Kauhajoki, and Ivalo, and two gynecological university hospital clinics in Helsinki and Oulu (Fig. 1). In 1997, another two STD outpatient clinics, one in Helsinki and one in Kuopio, joined the network. Patients can visit the clinics for suspected STI without an appointment and free of charge. The only exceptions are the student health clinics, which only care for registered university students, and the gynecologic clinics, for which a physician referral is needed and the visit is not free of charge. Because of the selection bias and the small number of patients with chlamydia, the data from the gynecologic clinics were excluded from the analysis.

Fig. 1

Fig. 1

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Data Collection

The data were collected with a self-administered, 21-point, anonymous questionnaire. All patients attending the STD clinic were asked to complete the questionnaire, and more than 97% agreed. Therefore, data were collected from patients with and without C trachomatis or other STIs. In the remaining non-STD network clinics, a questionnaire data were collected only from those patients with chlamydia, gonorrhea, syphilis, or HIV infection. In addition to demographic data (age, gender, occupation, nationality, place of residence), the questionnaire included also questions regarding the reason for the visit, which could have included symptoms (e.g., discharge, dysuria, abdominal pain) or screening for any STIs because of the patient’s, partner’s, or a physician’s initiative. Information regarding antibiotic or other treatment given for symptoms was also registered, and women reported the use of oral contraceptives or intrauterine devices. Information was collected from every patient regarding about the time and place of exposure, source partner (gender, relationship to the patient, nationality, STI notified or not), and other partners with whom the patient had sexual relations after the suspected infection was potentially acquired. A casual partner was defined as a partner who had been previously unknown to the patient or who the patient knew, but with whom the patient had intercourse without any other stable relationship. Sex workers were also registered as source partners for men. All other partners were regarded as regular partners, and included spouses, nonmarried partners living with the patient, or other partners who had a permanent relationship with the patient. Special questions focused on risk-taking behavior and registered the number of sex partners and STIs during the preceding 12 months. If needed, a trained nurse helped to interpret the questions. Questionnaires were available in Swedish and English.

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Diagnosis of Chlamydia

A physician checked the history and performed a clinical examination for each patient. Symptoms and signs were documented, and samples were routinely taken for chlamydia, gonorrhea, syphilis, and HIV infection. In 1995, the diagnosis of C trachomatis was based on urethral and cervical samples cultured in McCoy cells or examined with commercial immunoassay tests in laboratories that served the STD network clinics. 9,10 Beginning in 1996, first-void urine samples in males and cervical swab samples in females were examined with polymerase or ligase chain reaction. 10 In 1997, 63% of chlamydia samples in the STD clinics and 71% of samples in the non-STD clinics were examined with polymerase or ligase chain reaction tests. Gonorrhea was diagnosed by culture, and syphilis and HIV infection were diagnosed using serologic methods. In addition, genital herpes and human papillomavirus infection were diagnosed in the STD clinics by the presence of typical macroscopic lesions. During the 3-year study period, less than 1% of patients with chlamydia had a concomitant STI (mostly human papillomavirus infection).

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Statistical Methods

Each network clinic entered data in a computer using the same in-house software. The data from each center were compiled, and the present analysis was based on the material collected from all 12 network clinics from 1995 to 1997. The patient data from the STD and non-STD clinics were compared, as were data regarding patients with and without C trachomatis. Patients with other STDs (e.g., gonorrhea) were excluded from the analysis. The risk factor analyses were performed and expressed from data sampled from the entire 3-year period because annual subanalyses in the first and last year of the study gave the same risk factor results. Variables with normal distribution descriptive values were expressed by mean and standard deviations; statistical comparison between the groups was performed by t test, z test, or analysis of variance. Variables with ordinal descriptive values were expressed in median and interquartile range; statistical comparison between groups was performed using the Mann-Whitney test or Kruskal-Wallis test. Measures with a discrete distribution were expressed as counts (%) and analyzed by chi-square. No adjustment was made for multiple testing.

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Results

Incidence of C trachomatis in the STD Network Clinics and in Finland

In 1995 to 1997, the incidence of chlamydia increased slightly in Finland from 151 to 156 infections per 100,000 inhabitants. (Table 1). During that same period, 3686 patients with chlamydia (i.e., 16% of all cases notified by physicians in Finland) were encountered in the sentinel STD surveillance network. A total of 2,692 patients with chlamydia were registered among the 32,230 patients attending the STD clinics (Table 2). The overall detection rate was 8.4% (8.8% in men, 7.8% in women) and remained stable during the 3-year study period. A subanalysis in one STD clinic showed that the majority of patients had only a single visit during the study period, and there were only 31 (4%) such patients (26 men, 5 women) who presented twice for chlamydia.

Table 1

Table 1

Table 2

Table 2

The non-STD clinics in the network registered 997 patients with chlamydia (Table 2), half of whom (n = 488) were from student clinics and half (n = 509) of whom were from general healthcare clinics. The overall chlamydia detection rate was 5.3%, and decreased from 6% in 1995 to 4.7% in 1997.

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Demography of Patients With C trachomatis in the STD Network Clinics

In the STD clinics, there were more men (61%) than women with chlamydia, whereas in the non-STD clinics, infections in women (62%) outnumbered those in men (Table 3). The mean age of the patients with chlamydia was similar in the STD and non-STD clinics. The mean ages of men with chlamydia (26.6 years and 26.2 years, respectively) were significantly higher than the mean ages of women (23.7 years and 24.4 years, respectively). Overall, no changes in gender or mean age occurred during the 3-year study period.

Table 3

Table 3

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Comparison of STD Clinic Patients With and Without C trachomatis

Age of the patients.

The patients with chlamydia were significantly younger than those without chlamydia (Table 3). The mean ages of the men and women with chlamydia were 26.6 years and 23.7 years, respectively, and the respective mean ages of those without chlamydia were 31.7 years and 28.4 years.

The prevalence of chlamydia in different age groups is shown in Figure 2. The highest prevalence was encountered in the 15-year to 19-year group for males (14.3%) and females (15.9%). In the 20-year to 24-year group, the prevalence of chlamydia was 13.6% for men and 11.1% for women; in the 25-year to 29-year group, that prevalence was 10.8% for men and 6.3% for women.

Fig. 2

Fig. 2

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Contraceptive use.

Women with chlamydia used contraceptives significantly more often than women without chlamydia (59% versus 42%, Table 4). The difference was significant both for the use of oral contraceptives and intrauterine devices. This finding was also evident in women with chlamydia attending non-STD clinics (Table 4).

Table 4

Table 4

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Partners of the Patients With and Without C trachomatis in the STD Clinics

Source partners.

Men with chlamydia contracted infection significantly more frequently from a casual partner than from a regular partner (61% versus 37%, Table 5), whereas women were more at risk from regular partners.(39% and 61%).

Table 5

Table 5

There were small but significant differences between patients with and without chlamydia.(Table 5). Men with chlamydia had intercourse with casual partner more often than those without chlamydia (61% versus 58%); however, commercial sex workers had more seldom been partners of men with chlamydia than of men without chlamydia (2% versus 7%). Women with chlamydia had intercourse with a regular partner more often than those without chlamydia (61% versus 55%).

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Foreign partners and source countries.

Chlamydia was mainly contracted from a Finnish source partner. The partner was from outside of Finland in only 9% of men and 12% of women (Table 5). In men, the foreign source partner was most often met abroad (78%), whereas in women a foreign partner was met somewhat more often in Finland than abroad (56% and 44%). The percentages of foreign source partners remained stable during the 3-year study period.

When the patients with or without chlamydia are compared, foreign partners were somewhat more frequent in patients without chlamydia than in those with chlamydia (Table 5). Similarly, men and women without chlamydia had more often met their foreign partners abroad than men and women with chlamydia. A total of 7% of men and 5% of women contracted chlamydia abroad. The source countries were Russia and Estonia in half of men and in 20% of women. In addition, 30% of women contracted chlamydia from southern Europe.

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Second partners.

After intercourse with the source partner, one third of men and women with chlamydia had contact with a second partner before attending the STD clinic (Table 5). This finding was more common in men with chlamydia (35% and 30%) than men and women without chlamydia (31% and 25%).

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Time From C trachomatis Exposure to Diagnosis

The time from transmission of chlamydia to attendance at the STD clinics varied, but generally women attended for examination later than the men. The median time to attendance was 31 days for men and 37 days for women (Table 6). The time to attendance was highest (i.e., 46 days, 44 days) when the source partner was a spouse. The time to attendance was the shortest when the source partner was a casual contact (26 days, 36 days) or a sex worker (19 days).

Table 6

Table 6

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Partner and STD History of Patients With or Without C trachomatis

One third of men and 14% of women with chlamydia had five or more partners during the preceding 12 months (Table 7). A history of previous chlamydial infection was reported by 10% of men and 11% of women. Testing for HIV had been performed in 16% of men and 17% of women during the previous 12 months. No marked changes occurred during the 3-year study period.

Table 7

Table 7

When patients with and without C trachomatis were compared, men with chlamydia had had five or more partners during the preceding 12 months significantly more often than men without chlamydia (31% versus 17%, Table 7), but this difference was not as marked in women (14% versus 10%). During the preceding 12 months, 2.0% of men with chlamydia and 2.9% of men without chlamydia had had sex with men. The history of chlamydial infection during the preceding 12 months was also significantly more frequent in men and women with chlamydia (10% and 11%) than in those without chlamydia (5% and 7.5%) (Table 7).

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Discussion

During the study period, the incidence of chlamydia in Finland remained high (152/100,000 inhabitants). This incidence is in sharp contrast to that of gonorrhea (6.5/100,000 inhabitants). 1 The purpose of the present sentinel STD surveillance network was to obtain more epidemiologic information, especially regarding C trachomatis infection. The network consisted of 12 STD and non-STD clinics in all parts of Finland. During the 3-year period, 3,686 patients with chlamydia and 32,230 patients without chlamydia were registered. In Italy, a similar STD surveillance network consisting of 48 STD clinics registered 3023 patients with chlamydia during a 5-year period, but did not collect data from noninfected patients. 11 In the Finnish STD network, the prevalence of chlamydia was high (8.4%) among patients attending the STD clinic, and was lower (5.3%) among patients attending the non-STD clinics. At the end of the study period, more than 60% of the chlamydia samples were examined by polymerase or ligase chain reaction tests, which are more sensitive than the culture or the immunologic tests used in the beginning of the study. 10,12 However, the improved diagnostic tests do not seem to have any marked effect on the overall detection rate of chlamydia because in the last year of the study the prevalence increased only slightly in the STD clinic and decreased in the non-STD clinics. Two new STD clinics joined the network during the study, but this did not had any effect on the overall chlamydia detection rates because the prevalences in these two clinics were similar than in the other five STD clinics.

The prevalence of chlamydia was highest among women and men (16% and 14%) in the 15-year to 19-year age group. In the next two 5-year age groups, the prevalence was clearly lower in women but remained high in men. Women and men with chlamydia were significantly younger (mean ages, 24 years and 27 years) than patients who had not contracted chlamydia. That young age is a risk factor for chlamydia infection is in agreement with previous reports from genitourinary medicine clinics in England and Wales. 5,13

Women with chlamydia (59%) used oral contraceptives or intrauterine devices significantly more often than women without chlamydia (42%). Furthermore, women with chlamydia reported using condoms during the suspected intercourse only half as often (12%) as women who had not contracted chlamydia (25%). Therefore, it seems evident that the frequent use of oral contraceptives or intrauterine devices with simultaneous decrease in the use of condoms is a significant risk factor for chlamydia transmission in women. This finding is supported by that of Paukku et al, 14 who reported that the prevalence of chlamydia was high (5.6%) among women attending family planning clinics in Finland. A metaanalysis has also shown that the use of oral contraceptives involves an almost twofold risk for chlamydial infection, and when the use of barrier contraceptives is compared with oral contraceptives, the risk increases ninefold. 15

A high number of casual partners is also a well-known risk factor for chlamydia, gonorrhea, and other STIs. 16 We found that 32% of men and 14% of women with chlamydia reported a history of five or more partners during the preceding 12 months. As expected, the percentages were significantly lower in men and women who had not contracted chlamydia. Similarly, as many as 10% to 11% of men and women with chlamydia had been treated for chlamydia during the preceding 12 months, compared with 5% to 8% of men and women without chlamydia. These findings show that persons with frequent sex partners and previous chlamydial infection are a special risk and target group for safe-sex counseling.

We performed a detailed analysis of the source partners of patients with chlamydia. In 61% of men and 46% of women, chlamydia was contracted from a casual source partner, but as many as 37% of men and 61% of women contracted chlamydia from a regular partner. The present information regarding source partners was based on a questionnaire given to the patient, and was not confirmed by partner notification. A further study interviewing the source and other partners and checking their chlamydia test results would confirm whether the observed source-partner differences, especially those between the men and women, are of right magnitude. It is of interest that only 2% of men contracted chlamydia from a sex worker. This shows that sex workers are not an important source of chlamydia infection among Finnish men. In the Netherlands, however, Laar et al 17 reported that 11% of men visiting the STD clinic had contracted chlamydia from commercial sex workers.

The frequent spread of chlamydia to regular partners is not unexpected because the symptoms are often mild or even absent for a long period. 18,19 In the current study, we were not able to perform a detailed analysis of symptoms of chlamydia before or at presentation to the clinics. However, we could analyze the elapsed time from exposure to the diagnosis of chlamydia, and found that the median time to attendance at the STD clinic was 34 days and was similar for men and women. Interestingly, the time to attendance was highest when the source partner was a spouse, and shortest when the partner was a casual partner. Thus, after a casual sex contact, people seem to attend STD clinics rather rapidly for evaluation of possible C trachomatis and other STIs. A long time lap between exposure and diagnosis spreads chlamydia; one third of patients had already had sex with a second partner before they attended the STD clinic and were notified of their infection. In agreement with this finding, Irwin et al 20 reported that a high percentage of patients attending STD clinics reported sexual activity while symptomatic. However, we are aware of the limitations of the data based only on patients’ views about source partners and spread of chlamydia to second partners; therefore, the results regarding transmission and time to diagnosis should be interpreted with caution.

The current study confirmed that chlamydia is mainly endemic because more than 90% of infections were contracted in Finland. This finding is in sharp contrast to gonorrhea and syphilis infection, 50% to 70% of which are imported from abroad (often from Russia). 1,21 We also analyzed whether foreigners might be an important source of chlamydia transmission in Finland. The source partner was a foreigner for 12% of the women and 9% of the men with chlamydia. The women contracted chlamydia from a foreigner as often in Finland as they did abroad, whereas the men mostly contracted the infection abroad. Moreover, the percentage of foreigners attending the network STD clinics during the study period was less than 2%, and few of these patients had chlamydia. A higher percentage (10%) of foreigners with a new STD episode has been reported in the STD clinics in Italy (9% had contracted chlamydia). 22 These results show that approximately 6% of all chlamydia infections are contracted from foreigners visiting Finland, and approximately 12% are transmitted from foreign partners met abroad. Therefore, the import of chlamydia by foreigners or Finns from abroad seems to have no major effect on the present chlamydia epidemic in Finland.

In conclusion, the incidence of chlamydia remained continuously high in Finland, and 90% of the infections are endemic and spread around the country. The risk factors for chlamydia were young age, high number of sex partners, and the use of oral contraceptives or intrauterine devices. Men contract chlamydia more often from a casual than regular partner, whereas the opposite is true for women. The median time from exposure to diagnosis was 4 weeks, during which time further spread of chlamydia to a new partner was possible in one third of the cases.

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