**6. Complications**

Chlamydial infections are one of the most important causes of female infertility. Since infertility is one of the most significant issues to focus on chlamydia, it will be discussed in a separate section.

C.trachomatis is also the leading cause of PID. PID is a serious condition that may require hospitalization, intravenous antibiotic therapy, and tests to rule out a tuboovarian abscess. The risk of ectopic pregnancy is 7–10 times higher in women who have had PID than in those who have not. Pelvic adhesions involving the ovaries and tubes in 15% of women after PID may cause chronic pelvic pain in the long term. The case of perihepatitis, also known as Fitz-Hugh-Curtis syndrome, is a rare complication of PID, which is five times more common in chlamydia than in N. gonorrhea. Especially with serotype G infection, the risk of developing cervical cancer increases by about 6.5 times. Chlamydia infection also increases genital mucosal inflammation, facilitating HIV transmission.

A pregnant woman with a chlamydia infection can pass the infection to the baby during childbirth, and this can lead to pneumonia or conjunctivitis in the baby. Neonatal conjunctivitis, if remains untreated, can lead to blindness. Reiter's syndrome, reactive arthritis that may develop secondary to the immune response after primary chlamydia infection, is manifested by asymmetrical polyarthritis, urethritis, uveitis, mouth ulcers, circinate balanitis, and keratoderma blennorrhagica. The etiology is uncertain, but it usually follows an infectious attack and 80% of patients are HLA B27 positive. Other serious potential complications that can be related to chlamydia infection are miscarriage [41] and preterm birth [42].

There is no known association between chlamydia and tumor development in men, according to the evidence to date. However, this relationship in women has been reported by some authors. Paavonen et al. showed that the presence of enhanced antibodies to heat shock protein-60 is a high risk for cervical cancer; this also suggests that persistent *C. trachomatis* infection is associated with the development of cervical tumors [43]. One of the possible molecular mechanisms explaining the association of chlamydial infection with increased cervical cancer risk is that the infection generates an inflammatory response that triggers releases of ROS, cytokines, chemokines, growth, and angiogenic factors, leading to genetic instability and abnormal mitosis [44, 45]. *C. trachomatis* also affects beta-catenin and N-cadherin proteins, which have significant structural and regulatory roles [46]. In addition, there is evidence that CT infection increases HPV transmission and persistence. This coinfection increases the risk of cervical cancer as the epithelial destruction caused by the bacterium facilitates the entry of the virus; at the same time, with the weakening of the immune system, a microenvironment is formed that prepares the ground for the development of cancer [47, 48]. Anttila et al. found that the type of bacteria which bears the highest risk of developing cancer is the G serotype [49].

Since persistent inflammation is known to be related with tumor development, the ovaries may also be affected by chlamydia infection, as expected [50]. Shanmughapriya and colleagues showed that about 80% of ovarian cancer patients are infected with chlamydia [51]. Correspondingly, several studies have shown that the anti-Hsp60 protein is increased in ovarian cancer patients [52]. But despite these evidence, there are different consequences related to this issue, so more studies are needed to shed light on this topic [53].
