**3. Pathophysiology**

Although infection by C. trachomatis is a major sexually transmitted genital infection globally, eye infections may be also spread by personal contact and contaminated items which are touched or held by hands, such as towels, in areas with poor sanitation [8]. Repeated and chronic infections, usually in developing countries, can lead to trachoma, which is a chronic follicular keratoconjunctivitis that causes scarring and neovascularization of the cornea that can result in blindness [9].

In women, genital tract infections with by C. trachomatis are usually asymptomatic and that is why it is frequently characterized as the "silent epidemic" [10]. If left untreated though, it can lead to serious sequelae, including urethritis, bartholinitis, mucopurulent cervicitis, endometritis, salpigitis, and pelvic inflammatory disease which may subsequently compromise fertility or predispose to ectopic pregnancy. Additionally, several pregnancy complications have been linked to chlamydial infection, including chorioamnionitis, premature rupture of membranes, preterm labour and birth, low birth weight, intrauterine growth restriction and postpartum endometritis [11–15]. In males, (or men) may cause epididymitis, proctitis, prostatitis, urethritis and reactive arthritis [16].

In infants, C. trachomatis can cause conjunctivitis and/or pneumonia. More rarely, C. trachomatis occurs also in the vagina, urethra and rectum. Occasional C. trachomatis infection in children and adolescents (with no prior sexual activity) should be seen in the context of sexual abuse, especially when Chlamydiae are detected in the anorectal or genital region [17].

There are 18 serotypes of C. trachomatis. The genital strains belong to one of the serotypes D through K while trachoma strains to the serotypes A through C [18]. The most common genotype among infants is type E [19, 20].

## **4. Prevalence**

Based on prevalence data from 2009 to 2016, the estimated pooled global prevalence of chlamydial urogenital infection in women and men, aged 15–49 years,

#### *Chlamydial Infection DOI: http://dx.doi.org/10.5772/intechopen.96501*

was 3.8% and 2.7%, respectively [21]. Rates of infection among adolescent girls exceed 20% in many urban populations, but can be as high as 15% in suburban populations [22].

Worldwide, the prevalence of C. trachomatis in pregnant women varies from 1.0%–36.8%, while in high income countries it is estimated from 3%–14% [23]. Especially in European western countries, the prevalence of genital C. trachomatis infection in pregnant women based on nucleic acid amplification tests (NAAT) from either first void urine or a vaginal and/or endocervical swab, ranges from 3% to 6% [24]. However, prevalence may vary significantly during pregnancy among different continents [23] (**Figure 1**).

Approximately 50%–70% of infants exposed to an infected mother's genital flora during vaginal birth, will acquire chlamydia infection if no prophylaxis is given before or just after birth. More specifically, the 10%–20% of all infected infants will develop pneumonia and the 30%–50% conjunctivitis. Prevalence data of neonatal chlamydial conjunctivitis and pneumonia from several regions [25] are summarized in **Figure 2**.


#### **Figure 1.**

*Prevalence of C. trachomatis infection in pregnant women across all continents.*

**Figure 2.**

*Prevalence of chlamydial conjunctivitis and pneumonia in infants.*
