Bacteria, Epidemiology, Infectious Diseases

Chlamydia Basics: History, Symptoms, Diagnosis, Treatment, and Prevention

Author Chandana Balasubramanian , 02-Jul-2024

Chlamydia is the most common sexually transmitted disease worldwide. Caused by the bacteria Chlamydia trachomatis, it is the top bacterial infection reported in the United States. Despite being so prevalent, many people do not realize it also leads to blindness and can cause infertility issues [1, 2].


You can prevent Chlamydia with regular check-ups and better awareness of the risks. Early diagnosis and treatment are key to stopping the spread of the disease and avoiding severe long-term health problems.


Let’s explore the history, epidemiology, biology, symptoms, diagnosis, and treatment of Chlamydia. We will also discuss effective preventive strategies. 



The history of Chlamydia is a fascinating journey through time, marked by ancient texts, scientific breakthroughs, and evolving understanding. 

References to Chlamydia-like eye diseases appear in Egyptian and Chinese texts as early as 15 BC. 

The modern discovery of Chlamydia began in 1907 when German dermatologist Ludwig Halberstädter and Austrian bacteriologist Stanislaus von Prowazek conducted experiments on infected eyes. They identified chlamydial cytoplasmic inclusion bodies in the conjunctiva, leading to the initial identification of the pathogen [3,4].

Halberstädter and von Prowazek named the pathogen “Chlamydia,” derived from the ancient Greek word “chlamys,” meaning a short cloak worn by Greek soldiers. This name was inspired by the intracytoplasmic inclusions that looked like a cloak draped around the host cell nucleus. Initially, they thought it was a protozoan, but it was later considered a virus until electron microscopy in 1966 confirmed it as a bacterium [4].

It wasn’t until the 1970s that Chlamydia was recognized as a specific sexually transmitted infection (STI), and in 1988, it became a notifiable disease. Today, regular screening and increased awareness are crucial in preventing and treating this common yet often misunderstood infection [5].



Urogenital chlamydia infections are the most frequently reported bacterial infections in the U.S. and the leading cause of sexually transmitted infections worldwide [1]. In 2020, it was estimated that there were 128.5 million new chlamydia infections among adults aged 15-49 worldwide [6].

In 2020, it was estimated that 4.0% of women and 2.5% of men worldwide aged 15-49 were affected by Chlamydia [6].

In the U.S., women are twice as likely to have urogenital infections compared to men. The highest rates are seen in women aged 15-24 and men aged 20-24 [6].


How does it spread?

Chlamydia is sexually transmitted and spreads through unprotected vaginal, anal, or oral sex with an infected person. It can also be passed to a newborn during childbirth if the mother is infected [2].

Chlamydia trachomatis (C.trachomatis) is part of a family that also includes C.psittaci that causes parrot fever, and C.pneumoniae. 


Biology of the disease

Chlamydia has a unique life cycle with two stages: the elementary body (EB) and the reticulate body (RB). The EB, which is inactive, enters host cells and then changes into the active RB. The RB uses the host’s energy and nutrients to reproduce and create new EBs, which then infect more cells [7]. 

Chlamydia trachomatis targets specific areas: in women, it affects the endocervix (The endocervix is the inner cervix, which connects the uterus to the vagina, and produces mucus), and upper genital tract [7]. 

In both men and women, it targets the conjunctiva, urethra, and rectum [7].



Chlamydia often shows no symptoms. When symptoms do appear, it can take weeks after exposure. 

Even without symptoms, however, Chlamydia can cause serious health complications [2].

Chlamydia symptoms in females include: 

  • Unusual discharge from the vagina
  • Burning sensation while urinating
  • Bleeding in the middle of the menstrual cycle or after intercourse
  • Pain or discomfort in the lower abdomen [6].


Chlamydia symptoms for males include:

  • Burning during urination
  • Discharge from the penis
  • Pain in the testicles [6]. 


Newborn infants born to infected mothers might develop eye infections or pneumonia. Anal infections of chlamydia can result in pain, bleeding, and discharge from the anus [6].



Chlamydia is diagnosed by understanding the medical history and performing a physical examination. A urine test and a swab from the infected area may be taken for further testing. 

The gold standard for Chlamydia diagnosis is the molecular test NAAT (nucleic acid amplification testing) using swabs or urine samples [1]. 

Since many infections are asymptomatic, regular testing is sometimes recommended.



Chlamydia is treated with antibiotics like azithromycin or doxycycline. However, early intervention is advised because treatment cannot reverse permanent damage already caused by the infecting bacteria [2, 8].


  • Use condoms during vaginal and anal sex.
  • Pregnant women should get routine testing to prevent passing the infection to their babies.
  • Repeat infections are common, so getting tested again three months after treatment is important.
  • Ensure all partner(s) are treated to avoid reinfection [7,8].


Vaccine development

Efforts to develop a vaccine against Chlamydia are currently underway, with a particular focus on the sexually transmitted Chlamydia trachomatis. There is an urgent need for effective vaccines against various members of the Chlamydia genus.

Whole-cell Vaccines

Whole-cell vaccines have shown protection against genital challenges in mice. However, these vaccines are unlikely to be effective in humans due to the risk of delayed hypersensitivity and reinfection [9].

Subunit Vaccines

Subunit vaccines use specific parts of the bacteria to stimulate an immune response without using the whole bacteria. 

  • Major Outer Membrane Protein (MOMP): This protein is used as an antigen in the vaccine and has shown promising results in mice and human trials for trachoma, a Chlamydia-related eye infection.
  • Polymorphic Membrane Proteins (Pmps): These proteins have also been effective in protecting mice from Chlamydia in experiments [9].



The European Union-funded VacPath project is developing a vaccine that targets the bacterium immediately after it enters the genital tract, aiming to provide early intervention and protection [10].



Understanding Chlamydia and its implications is crucial in today’s world, where it remains the most common sexually transmitted disease globally. Caused by the bacteria Chlamydia trachomatis, this infection is the top bacterial infection reported in the United States. Despite its prevalence, many are unaware that Chlamydia can lead to blindness and infertility issues.

Prevention through regular check-ups and increased awareness about the risks is essential. Early diagnosis and prompt treatment can help prevent the spread of the disease and avoid serious long-term health complications. Chlamydia’s journey from ancient texts to modern medical breakthroughs highlights the importance of continuous research and education.

By learning about Chlamydia’s history, epidemiology, biology, symptoms, diagnosis, treatment, and prevention strategies, we can better equip ourselves to tackle this common yet often misunderstood infection. Efforts in vaccine development are promising and offer hope for a future where Chlamydia can be effectively prevented and controlled. Regular screening, safe sexual practices, and staying informed are key steps in combating Chlamydia and protecting public health.


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Learn more about more bacterial infections on the GIDEON platform.




[1]M. Mohseni, S. Sung, and V. Takov, Chlamydia. StatPearls Publishing, 2023.
[2]CDC, “About,” Chlamydia, 21-May-2024. [Online]. Available: [Accessed: 02-Jul-2024].
[3]C. M. Black, “Introduction,” in Issues in Infectious Diseases, S. Karger AG, 2013, pp. 1–8.
[4]C. M. Black, Ed., Chlamydial Infection: A Clinical and Public Health Perspective. S. Karger AG, 2013.
[5]M. Worboys, “Chlamydia: A disease without a history,” in The Hidden Affliction, Boydell and Brewer Limited, 2019, pp. 153–184.
[6]“Chlamydia,” [Online]. Available: [Accessed: 02-Jul-2024].
[7]C. Elwell, K. Mirrashidi, and J. Engel, “Chlamydia cell biology and pathogenesis,” Nat. Rev. Microbiol., vol. 14, no. 6, pp. 385–400, 2016.
[8]C. E. Van Ommen, S. Malleson, and T. Grennan, “A practical approach to the diagnosis and management of chlamydia and gonorrhea,” CMAJ, vol. 195, no. 24, pp. E844–E849, 2023.
[9]L. M. de la Maza, T. L. Darville, and S. Pal, “Chlamydia trachomatisvaccines for genital infections: where are we and how far is there to go?,” Expert Rev. Vaccines, vol. 20, no. 4, pp. 421–435, 2021.
[10]S. Abraham et al., “Safety and immunogenicity of the chlamydia vaccine candidate CTH522 adjuvanted with CAF01 liposomes or aluminium hydroxide: a first-in-human, randomised, double-blind, placebo-controlled, phase 1 trial,” Lancet Infect. Dis., vol. 19, no. 10, pp. 1091–1100, 2019.
Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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