Epidemiological features and determinants for Chlamydia trachomatis infection among women in Catalonia,Spain

Abstract

We determined the prevalence of Chlamydia trachomatis (CT) infection and risk factors for its acquisition by women aged less than 35 years who were attending sexual health centres in the province of Barcelona in 2007. A convenience sample of 397 adolescents and young adult women aged between 16 and 35 years, stratified by age and recruitment site, were tested using realtime polymerase chain reaction by CT DNA. A standardized questionnaire was used to collect epidemiological and behavioural data on the participants, which were analysed in a multivariate logistic regression model. The overall prevalence of CT was 4%, significantly higher in those under 25 years of age (5.8% versus 1.6% over 25). The independent risk factors for CT infection were: foreign origin (odds ratio [OR] 4.7; confidence interval [CI] 1.02–21.8), having had a sexual partner in the last three months (OR 4.59; CI 1.16–18.08) and tobacco use the last 12 months (OR 6.38; CI 1.16–34.93). In conclusion, this is the first study performed in Catalonia showing a high prevalence of CT in young women, consistent with trends in the rest of Europe. Systematic monitoring of CT infection in sentinel populations such as this will inform future targeted screening programmes in our setting.

Keywords

STI prevalence women risk factors sexual behaviour

INTRODUCTION

Genital infection by Chlamydia trachomatis is one of the most frequent sexually transmitted infections (STIs) in the world,¹ especially in young people aged less than 25 years and in women of child-bearing age. This infection is asymptomatic in up to 85% of cases and not being treated can cause important sequelae.²

The prevalence of C. trachomatis has been increasing since the turn of the 20th century.³ Therefore, several countries have started population-based and others opportunistic targeted screening for C. trachomatis.^1,4,5 Some screening programmes have shown a reduction in the incidence of infection and have shown their effectiveness at reducing prevalence rates;^4,6,7 however, this effectiveness has been questioned in others.^2,4 Therefore, the effectiveness of screening remains unsolved, since there is not sufficient evidence to demonstrate it.

As in Catalonia, Spain, C. trachomatis has been a quantified notifiable disease since 1992. At present, it is one of the most common STIs, and in 2003 we saw a significant increase (83.6%). The rise has been consistent over the past three years, with an incidence rate of 5.1 cases per 100,000 inhabitants in 2006.⁸ Nevertheless, data from the notifiable disease registry cannot explain or describe the epidemiological profile of the affected population or the distribution in the prevalence of this infection. In Spain, prior studies have been performed to determine the prevalence of C. trachomatis in populations with an average age higher than the expected peak incidence.⁹ In addition, some of these studies used less sensitive detection methods rather than nucleic acid amplification: as a result, lower prevalences may have been detected.¹⁰

In order to implement recommended C. trachomatis control strategies, specific studies must be carried out to estimate prevalence rates and describe epidemiological and behavioural characteristics among the must vulnerable populations in Catalonia.^11,12

The aims of this study were to determine the prevalence of C. trachomatis infection using molecular testing (realtime polymerase chain reaction [PCR]), describe epidemiological and behavioural characteristics and ascertain risk factors for acquisition by sexually active young women.

MATERIALS AND METHODS

The study was carried out between September 2006 and March 2007, after approval by the ethics committee of Hospital Universitari Germans Trias i Pujol (HUGTIP), using a cross-sectional convenience sample of 397 women. The inclusion criteria were as follows: to have been sexually active during the previous 12 months and to be aged between 16 and 35 years.

The study population was recruited from attendees at sexual and reproductive health centres (d'Atenció a la Salut Sexual i Reproductiva, ASSIR) in three areas of the province of Barcelona, or at the Youth Health Centre for Contraception and Sexuality (Centre Jove d'Anticoncepció i Sexualitat, CJAS) in Barcelona city. These centres offer family planning services including education, specific care for young people, mother-and-child care, and prevention, care and diagnosis of general gynaecological conditions.

The sample size was calculated using the finite population formula. The sample was stratified by age and recruitment site. The prevalence of C. trachomatis was estimated at 10% for young women under 25 years and 5% for those who were over 25 years with a 2.2% level of significance. The total sample was composed of 397 women.

Endocervical samples were collected using the Multi-Collect Specimen Collection Kit (Abbott Molecular Inc, Abbott Park, IL, USA). The samples were transported, stored and analysed in the microbiology laboratory of the HUGTIP, a period not exceeding 14 days from collection: the whole process followed the manufacturer's specifications. For the detection of C. trachomatis, we used a molecular technique based on realtime PCR (Abbott Real Time Chlamydia trachomatis/Neisseria gonorrhoeae assay, Abbott Molecular).¹³ A standardized questionnaire was applied in an interview with a health-care professional from each participating centre. No personal identifying information was used, thus ensuring anonymity and a single data management system so that sociodemographic, epidemiological and behavioural data could be collected. This information was entered into a database (Microsoft Access^®) created for quality control and management.

Demographic, epidemiological and behavioural data of the study population were analysed using SPSS software (v. 18.0, SPSS Ibérica, S.L.U). Univariate and multivariate logistic regression models were used to evaluate the sociodemographic and behavioural variables associated with C. trachomatis. A final multivariate model was performed with inclusion of all variables that were significantly associated with C. trachomatis in univariate models and remained significantly associated in the final multivariate model. Adjusted odds ratio (OR) and their respective 95% confidence intervals (CI) were calculated. Statistical significance was set at 0.05.

RESULTS

A total of 397 sexually active women were included for analysis of whom 206 of the group were aged under 25 years and 191 aged 25 years or over. In total, 81.1% were recruited in ASSIR centres and the remaining 18.9% in the CJAS. The mean age was 27 years (SD, 4.8), and 86.1% were Spanish. In all, 85.6% were educated to primary level. The main reason for attending the clinic was a regular gynaecological check-up (69.3%). The main sociodemographic and behavioural characteristics of the study population are shown in Table 1.

Table 1

Sociodemographic and behavioural characteristics (n = 397)

Variables	Frequency	(%)
Age group
25 years	206	51.9
<25 years	191	48.1
Origin
Foreign	42	10.6
Spanish	355	89.4
Educational level
Primary	340	85.6
Secondary	57	14.4
Centre
ASSIR	322	81.1
CJAS	75	18.9
Reason for consultation
STI/HIV test	41	10.3
Gynaecological check-up	275	69.3
Other	81	20.1
Partner type
Monogamous	360	90.7
Concurrent	32	8.1
Number of sexual partners in past 12 months
Less than 2	292	73.6
Two or more	105	26.4
New sexual partner in past three months
Yes	67	17.6
No	313	82.4
Use of condom, last sexual contact
Yes	210	53.4
No	183	46.6
Use of postcoital pill
Yes	105	26.5
No	291	73.5
Abortion in past 12 months
Yes	42	10.7
No	352	89.3
Symptoms of Chlamydia trachomatis infection
Yes	5	1.3
No	370	98.7
Previous STI
Yes	42	11.2
No	334	88.8
HIV status
Known	124	31.2
Unknown	273	68.8
Sex worker
Yes	20	5.1
No	371	94.9
Contact with HIV/STI-infected persons
Yes	12	3.2
No	363	96.8
Travel outside Spain in past 12 months
Yes	145	36.6
No	251	63.4
Drug consumption in past 12 months
Yes	232	58.6
No	164	41.4
Consumption of tobacco in past 12 months
Yes	182	46.1
No	213	53.9
Consumption of cannabis in past 12 months
Yes	84	21.3
No	310	78.7
Consumption of alcohol in past 12 months
Yes	93	23.6
No	301	76.4
Consumption of injected drugs in past 12 months
Yes	1	0.3
No	392	99.7
Consumption of non-injected drugs in past 12 months
Yes	16	4.1
No	378	95.9
Consumption of designer drugs in past 12 months
Yes	7	1.8
No	387	98.2
Contact in past 12 months in places where sex is available
Yes	17	4.3
No	378	95.7
Sex with partners from specific sites
Saunas	4	1
Bars	10	2.5
Internet chat rooms	5	1.3
Others	0	0
Sexual practices
Vaginal sex	370	93.9
Anal sex	81	21
Oro-anal sex	27	7.1
Oral sex	301	76.2

STI = sexually transmitted infection

Regarding sexual and drug use behaviours, the mean age at the first sexual contact was 17.16 years (SD, 3.1); 46.6% did not use a condom the last time they had sex. Of this group, 66.2% reported not having used a condom with their stable partner. The average number of sexual partners in last year was 1.59 (SD, 1.6). A total of 26.4% had had two or more sexual partners during the previous 12 months, and 17.6% reported having had a new partner during the previous three months. As for drug use, most participants had consumed drugs during the previous 12 months (58.6%), the most commonly consumed drug being tobacco (46.1%), followed by alcohol (23.6%).

Overall prevalence of C. trachomatis was 4% (n = 15). By age group, the prevalence of infection by C. trachomatis was 5.8% for those aged under 25 years and 1.6% for those aged 25 years or over: the difference was statistically significant (P = 0.02).

Possible factors associated with acquisition of these infections were analysed using a univariate model and a multivariate model (Table 2). The factors that were significantly associated with the presence of C. trachomatis were foreign origin, aged under 25 years, having had two or more sexual partners during the previous 12 months, having had a new sexual partner during the previous three months, having had concurrent partners during the previous 12 months, symptoms of infection, having had relationships with people diagnosed with any STI, having had sexual contact during the previous 12 months in places where sex is available (such as saunas) or meeting sexual partners via Internet chat rooms, and taking drugs during the previous 12 months, among which were tobacco and cannabis.

Table 2

Univariate and multivariate analyses of risk factors associated with Chlamydia trachomatis

		Unadjusted		Adjusted
Variables	CT (%)	OR	95% CI	OR	95% CI
Origin
Foreign	9.5	3.29	(0.9–10.8)	4.709	(1.017–21.817)
Spain	3.1	Referent		Referent
Age group
25 years	5.8	3.87	(1.077–13.95)	–	–
<25 years	1.6	Referent
Number of sexual partners in past 12 months
<2	2.4	Referent	(1.18–9.5)	–	–
>2	7.6	3.35
Symptoms of Chlamydia trachomatis infection
Yes	20	6.35	(0.66–60.64)	–	–
No	3.8	Referent
New sexual partner in past three months
Yes	11.9	6.9	(2.32–20.72)	4.593	(1.12–18.08)
No	1.9	Referent		Referent
Contact with HIV/STI infected persons
Yes	16.7	7.06	(1.36–36.5)	–	–
No	2.8	Referent
Drug consumption in past 12 months
Yes	5.6	4.8	(1.07–21.6)	–	–
No	1.2	Referent
Consumption of tobacco in past 12 months
Yes	7.1	8.1	(1.8–36.4)	6.38	(1.16–34.93)
No	0.9	Referent		Referent
Consumption of cannabis in past 12 months
Yes	9.5	4.55	(1.602–12.9)	–	–
No	2.3	Referent
Contact in past 12 months in places where sex is available
Yes	17.6	6.5	(1.65–25.8)	–	–
No	3.2	Referent
Contact in past 12 months in saunas where sex is available
Yes	25	9.66	(0.94–99.3)	–	–
No	3.3	Referent
Contact via Internet chat rooms in past 12 months
Yes	20	7.2	(0.75–69.2)	–	–
No	3.3	Referent
Partner type
Monogamous	12.5	4.6	(1.37–15.3)	–	–
Concurrent	3	Referent

CT = Chlamydia trachomatis; OR = odds ratio; CI = confidence intervals

The significant variables were included in a multivariate regression model, where it was observed that having had a new sexual partner during the previous three months (OR 4.6), foreign origin (OR 4.7) and smoking during the previous 12 months (OR 6.4) continued to be independent risk factors for acquisition of C. trachomatis infection.

DISCUSSION

This is the first study in a group of young women in Catalonia to estimate the prevalence of C. trachomatis using molecular tests, which obtained a higher prevalence of C. trachomatis in the general Spanish population, especially in women aged under 25.

Few studies in Spain have used molecular tests to study the epidemiological and behavioural characteristics of young people. These studies have mainly been carried out among STI/HIV vulnerable groups, such as commercial sex workers, and obtained prevalences ranging from 4% to 6%.^14–16 The few studies carried out in the general population using PCR detection techniques showed lower prevalences, around 2%.^17–19

In Europe, the prevalence of C. trachomatis infection ranges from 2% to 17% depending on the country, population and setting.^20,11 The overall prevalence of C. trachomatis infection in this study was 4%, which is similar to that obtained in the UK by Wilson et al.,²¹ where a mean prevalence of 4.1% was observed in the general population in the same age group as ours (16–35 years) and using similar detection techniques.

If we analyse the prevalence for the two age groups included, we find that the differences found are consistent with those observed by other authors. A systematic review performed in the UK by Adams et al. ²² found that the mean prevalence in young people aged under 25 years was 6.6%. For those aged over 25 years, Adams et al. observed a mean prevalence of 2%, which was similar to the prevalence we observed.

The risk factors associated with C. trachomatis infection found in this study are consistent with those of previously published studies.^23–25

Regarding country of origin, several studies have also measured higher prevalence among foreign subjects compared to the local population.^19,26 In our study, 81.2% of the foreigners analysed were from Latin American countries, with features similar to those of the Spanish population with reference to sexual behaviour and drug use. The Spanish health service provides universal coverage and, therefore, immigrants have the same access to these services than the native population, but the majority have an unfavourable socioeconomic and psychosocial situations.^27,28 As C. trachomatis rates in their countries of origin are very high, estimated at 9.5 million new cases annually,²⁹ this probably also contributes to the higher prevalence found in this study for foreign participants.

The other associated factor was tobacco use during the previous 12 months. In Catalonia, 20.9% of women and 30.3% of men smoke. The population group with the highest rate of smoking (33.3%) falls within the age group of the present study.³⁰ The characteristics of our questionnaire did not enable us to stratify tobacco use by amount consumed; therefore we could not stratify the degree of risk associated with this measure. As seen in other studies, young people who smoke have more risk behaviours than non-smokers and, therefore, a greater risk of infection.³¹ It has been established that smoking can cause or at least favour a series of disorders, including damage of cervical and uterine tissue and an immunosuppressive effect that increases three-fold the risk of infection by C. trachomatis.^32,33

The risk factor of having a new sexual partner during the previous three months is consistent with other data,^{1,12,24,34,35} which show this to be a risk factor for C. trachomatis infection. Rate of sexual partner change is a critical variable relevant to the spread of C. trachomatis within the population.

Among the limitations of the study we note that the results may not be generalized to all women in Catalonia, since the study was performed only in four ASSIR centres with a small sample. However, these centres are characterized by universal coverage with equal access to benefits offered to the entire female population, and therefore the demographic and behavioural characteristics of women attending these centres are likely to be similar to those of the general population,³⁰ minimizing the selection bias. Secondly, we also attempted to minimize information bias by the use of a confidential anoymised questionnaire.

Despite these limitations the results are consistent with trends found elsewhere in Europe in the epidemiological characteristics and the prevalence of C. trachomatis in young people. We highlight the need for improved reporting of this infection in Catalonia, to better monitor the actual characteristics of the populations affected. Systematic monitoring of these infections in sentinel populations of young people is warranted in order to assess the impact of any screening programmes in our setting. For this reason, as part of the Integrated HIV/STI Surveillance System in Catalonia and to improve current monitoring systems, monitoring of the prevalence of C. trachomatis infection and risk factors for transmission has begun in different surveillance populations that are more susceptible to acquire or transmit these infections: commercial sex workers, men who have sex with men, intravenous drug users and, from 2006 onward, young people, for whom higher prevalences than expected were obtained in the present study.

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