**3. Epidemiology of** *C. trachomatis* **infection**

*C. trachomatis* is the most common sexually transmitted infection causing cervicitis in female [2]. Chlamydial infections affect mainly young females between 16 and 24 years of age. According to the recent literature, a high number of sexual partners, unprotected sex, being unmarried, young age, low educational level, high-risk human papillomavirus (HPV) positivity, and black ethnicity increase the risk of chlamydial infections [4, 7]. Several studies have shown that the estimated prevalence of chlamydial infection vary between 1 and 12% [3–5]. Specifically, while the prevalence rate in the UK was reported as 10.3%, in Switzerland and France the prevalence rates were 2.8% and 3%, respectively. In a study group with a large number of individuals, the overall prevalence of chlamydial infection was 9.2%, with a peak of 12.2% among the 17-year-old women [8]. Ghazal-Aswad et al. investigated the prevalence of chlamydia infection in a middle eastern community and they reported that the estimated prevalence rate was about 2.6% and extremely higher in women screened in secondary care [9]. In a study from Brasil, the overall prevalence of *C. trachomatis* infection was

Chlamydia trachomatis *Infection in Women DOI: http://dx.doi.org/10.5772/intechopen.111755*

reported as 11%, whit the highest prevalence seen in women between 16 and 20 years of age [10]. More recently, in a study from China, it has been shown that the overall prevalence of *C. trachomatis*, HPV, and *C. trachomatis*/HPV coinfection was 4.7%, 15.5%, and 1.2%, respectively, while the prevalence of asymptomatic infection of that was 3.8%, 10.8%, and 0.6%, respectively [11].

More importantly, studies have shown that prevalence rates range from 2 to 17% in asymptomatic women, which provides the importance of screening tests. In a screening study from France, it has been shown that there was a large difference between tested populations, ranging from 6 to 11% in women attending family planning centers, 1–3% in women attending preventive medical centers [4]. More recently in a study from India, prevalence of chlamydia infection was assessed among women visiting a gynecology outpatient clinic. In this study, the evaluation was performed by an in-house PCR assay. The authors reported 23% positive cases and chlamydial infection was predominantly seen between the ages of 18 and 33 years [12].
