Chlamydia is the most common bacterial infection transmitted sexually in Europe and it is particularly common in young people. According to the World Health Organization, 10% of sexually active people under 25 years of age may be infected.1 Chlamydia can affect both men and women, but complications are more common in women. Based on official data from the European Center for Disease Prevention and Control,2 certain socioeconomic statuses and sexual behaviors are associated with increased vulnerability to sexually transmitted infections (STIs).3

According to studies of different populations in Europe, the estimated prevalence of Chlamydia trachomatis infection, or chlamydia, is between 4% and 6%.4,5,6 Up to 70% of infections in women are asymptomatic,7 and chlamydia increases the risk of infection by the human immunodeficiency virus and other STIs, such as gonorrhea.8 Notification of individual cases of genital chlamydial infection is not a requirement in Spain, where epidemiological surveillance is organized through the Microbiological Information System. In Catalonia, where our hospital is based, the number of cases of genital chlamydia must now be reported, a requirement that led to a 29% increase in the number of cases reported between 2011 and 2012.9

We performed a prospective descriptive study of the frequency of chlamydia in patients seeking treatment for a suspected STI at the STI unit of Hospital Universitario Arnau de Vilanova in Lleida between November 2012 and November 2013. All patients were asked if they wished to participate in the study and those who agreed signed an informed consent form.

During the visit, apart from history taking and tests relevant to the patient's presenting condition, each patient was asked if they would provide samples (urethral for men and cervical for women) to test for chlamydia. The detection methods used were the polymerase chain reaction nucleic acid test (Anyplex CT/NG Real-time Detection, Seegene) and immunochromographic antigen detection. Patients diagnosed with C trachomatis infection were given cards to pass onto their sexual contacts to come in for evaluation.

Information on the study variables was collected in face-to-face interviews with the patients (Table 1). The prevalence of chlamydial infection in the subgroups analyzed was calculated with 95% CIs. Associations between the dependent variable (chlamydia) and the main independent variables were assessed by odds ratios and 95% CIs.

In total, 107 patients (68.2% men) were included in the study. Most (71.1%) had secondary or university studies. Almost 40% of the patients were aged between 26 and 35 years, 58.9% stated that they did not generally use contraception methods, and 5.6% reported working as a sex worker. Genital warts were the most common presenting complaint, present in 47.7% of patients.

The prevalence of chlamydia was 9.3% (10 of 107 patients; 95% CI, 3.8-14.9). This rate provides additional strength to guideline recommendations to screen for C trachomatis infection in all patients seeking treatment for a suspected STI. The odds of being infected was 11.1 times higher (95% CI, 3.4-72.4) in patients who reported having had 2 sexual partners (compared with 1 or none) in the previous month and 5.3 times higher (95% CI, 0.9-31.7) in patients with 3 or more sexual partners (also compared with 1 or none) in the past year. The odds of infection was also higher in homosexual patients (OR, 5.5; 95% CI, 1.2-26.1), in patients who reported working as sex workers (OR, 5.7; 95% CI, 0.9-36), and in patients with gonorrhea (OR, 49; 95% CI, 3.0-794.4); 66.7% of all the patients with gonorrhea had chlamydia. Associations between C trachomatis infection and the other study variables (Table 2) could not be determined due to insufficient statistical power.

Our study has certain limitations. Because information on sexual orientation, sexual habits, and sexual partners was collected during patient interviews, its reliability may be questionable. Nevertheless, all interviews were conducted by trained STI experts in an appropriate, confidential setting. While the detection techniques used were highly sensitive and specific, it should be noted that results may vary according to the quality of the biological sample. Finally, we studied a relatively small sample of patients, and consequently the study was not sufficiently powered to detect certain risk factors. Small samples can also result in imprecise estimates with wide confidence intervals. Notwithstanding, despite the limited size of the sample analyzed, we found 2 risk factors significantly associated with chlamydial infection that have been reported in numerous studies,5,8,10 namely, number of sexual partners in the previous month and homosexual relationships.