Introduction

Chlamydia is an infection caused by the bacterium Chlamydia trachomatis. 

Chlamydia is a sexually transmitted infection (STI), and is one of the most common STIs worldwide. There are over 130 million new cases reported to the WHO (World Health Organisation) every year, although this is likely to be an underestimate as not all cases will be reported. It can be transmitted via vaginal, anal or oral sex. Chlamydia can also be transmitted from mother to child during childbirth. 

Chlamydia is a treatable infection- the usual treatment is oral antibiotic azithromycin (usually one tablet 1000mg, single dose) or doxycycline (usually 100mg, twice daily, given over the course of a week). Azithromycin is generally preferred as it is a single dose. In chlamydial cases where there is no complication, antibiotic therapy is 95% effective. It is important to take medications as instructed in order to completely cure the infection. Sexual activity is also advised against for a week after the infection to avoid spreading to others. Reinfection however can occur from different sexual partners.

Most cases of chlamydia are asymptomatic, so the person infected would not necessarily know that they had the infection without being tested, and therefore would not know if they have passed it on to any sexual partners. Asymptomatic infections are around 70-80% of cases in those assigned female at birth and around 40-50% of those assigned male at birth. 

Groups that are considered at a higher risk of acquiring an STI, like chlamydia are people with multiple sexual partners, men who have sex with men, and those with a history of STI. It is common for chlamydia and gonorrhoea to co-occur, and so individuals should be tested for both. Pregnant women should also be tested at a prenatal appointment to reduce the risk of transmission to the newborn.^1,2 

Common symptoms

For those assigned female at birth, cervicitis (inflammation of the cervix) is the most common result of chlamydia infections. In around 70% of cases, this is asymptomatic. In only a minority of women, there will be symptoms of: a change in vaginal discharge, bleeding during sex, bleeding in between menstrual periods, pain in the abdominal area or a burning sensation while passing urine. 

Common symptoms in those assigned male at birth include discharge from the penis, pain in the testicles, and a burning sensation when passing urine. The prostate gland can also become inflamed, known as prostatitis, which can also cause pain while urinating. 

Proctitis, which is inflammation around the rectum (anal) area, is usually seen in men who have sex with men (although anal sex occurs between heterosexual partners also). This is usually asymptomatic also but can cause pain and bleeding if there are symptoms.³

Trachoma

Chlamydia can spread from person to person by physical contact with the discharge of the eyes or nose and can infect the eyelids (conjunctiva). The infection can also be passed on via a mosquito that acts as a vector for the disease.

Repeated infections within the eye can lead to a condition called trachoma. Trachoma causes the conjunctiva to be severely scarred, and so the eyelashes turn inwards and these scratch the surface of the eye. This can make blinking very painful. The scratches damage the cornea, making it opaque and over time a build-up of these opacities will cause a person to lose their vision. 

Trachoma is most commonly found in low-income countries, and particularly in Ethiopia. It commonly spreads within families- particularly people assigned female at birth (who are affected around four times as often as people assigned male at birth) and children. Trachoma is the leading infectious cause of blindness worldwide and around 1.9 million people are estimated to be blind or visually impaired as a result of trachoma. Vision loss by trachoma is not reversible. 

There is surgery available to correct the inwardly turned eyelids (which will relieve pain and prevent further damage to the cornea) and also prophylactic antibiotics which are given to everyone in the population to reduce spread. Whilst this is available in many parts of the world where trachoma is endemic, issues around access to treatment continue to be prevalent. 

Neonatal chlamydia 

A newborn can acquire chlamydia from the mother during childbirth if delivered vaginally. This occurs in around 15-30% of babies born to mothers with chlamydia. The two main manifestations of this are conjunctivitis and pneumonia. Pneumonia is an infection of the lower respiratory tract. Usually, neonates are diagnosed within the first 8 weeks of life and usually present with nasal congestion and a cough. 

These infections can be treated with azithromycin and usually do not cause any long-term complications for newborns.

Complications of chlamydia 

Although chlamydia is a treatable (and curable) infection, if left untreated, it can cause long-term damage. Chronic pain in the reproductive organs and pelvic area can occur due to the damage caused. 

Urethritis is more commonly seen in people assigned male at birth rather than those assigned female. This causes pain when urinating. 

Those infected with chlamydia are significantly more likely to be infected with HIV due to certain molecules of the immune signalling pathway increasing the susceptibility to other infections, and so should consider being tested for HIV too.⁴ 

Complications with female fertility 

Repeated infections of chlamydia can permanently damage the fallopian tubes by the buildup of scarred tissues, blocking the path for an egg to reach the uterus (where it would be fertilised). 

Pelvic inflammatory disease is another long-term complication of untreated chlamydia. This occurs when the infection spreads from the cervix to the upper reproductive tract. A diagram is shown below (source) to show the female reproductive system. The most common symptoms of pelvic inflammatory disease are abdominal or pelvic pain. Other symptoms include nausea, vomiting, fevers, chills, low back pain, pain during sex and pain during urinating. It can also increase the chance of an ectopic pregnancy where the egg is fertilised in the fallopian tubes, rather than in the uterus and so will affect the foetal growth. 

A study conducted in the USA found that women who were more likely to have an STI during pregnancy were often those who did not receive adequate medical care, were less likely to have been in a committed relationship, and were likely to smoke during pregnancy. 

Complications with male fertility

In males, the epididymis, which is the tube (diagram, source, showing male reproductive system) through which sperm travel out of the testicles, can be inflamed by a chlamydial infection, causing epididymitis. Symptoms include pain in the testicle (usually on one side), and pain when urinating. Long term or severe epididymitis can damage these tubes, and scar the sperm ducts, which can reduce the fertility if the sperm are unable to leave the testicles.⁵

Informing partners 

If an individual is diagnosed, they should notify their sexual partners so that the partners can be tested themselves. It is however acknowledged that there is still considerable stigma around STIs. This can be both while disclosing sexual history to the healthcare provider (say a GP or at a clinic) or while informing sexual partners. This can be especially true in cases of sex workers or where there has been trauma or abuse. From a moral standpoint, it is important to create an open discussion around STIs to try to limit their spread (and consequences if left untreated), but this may well be easier said than done.⁶ 

Summary 

Chlamydia is a very common sexually transmitted infection. It is mostly asymptomatic and so people will not necessarily know that they have it until a later stage. Symptoms in those assigned female at birth include unusual discharge and bleeding from the vagina, pain during sex or while urinating and pain in the lower abdomen. In those assigned male at birth, symptoms include pain in the testicles and pain while urinating. If left untreated, it can lead to infertility in both males and females. For males, this can involve inflammation, leading to scarring and damage of the tubes that carry sperm from the testicles to the penis. For females, it can lead to pelvic inflammatory disease, where the fallopian tubes can be scarred and damaged. Those who are sexually active, and have multiple sexual partners and who do not use protection (like condoms) should get themselves tested regularly for early detection of STIs.