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Human pap smear showing clamydia in the vacuoles at 500x and stained with H&E.

Image : “Pap smear showing clamydia in the vacuoles” by Unknown. License: Public Domain

Definition and Overview of Chlamydia

Chlamydia — gram-negative bacteria

The family of Chlamydiaceae contains 3 human pathogens:

  • Trachomatis
  • Psittaci
  • Pneumoniae

Chlamydiae are immobile, gram-negative bacteria. The cell wall does not contain a peptidoglycan layer, but lipopolysaccharides. Common to all chlamydia is their complex reproduction cycle. Due to a defect in their own energy metabolism, chlamydia is dependent on that of its host.

Chlamydiae have the ability to establish long-term associations with host cells. When an infected host cell is starved for various nutrients such as amino acids (for example, tryptophan), iron, or vitamins, this has a negative consequence for Chlamydiae since the organism is dependent on the host cell for these nutrients. Long-term cohort studies indicate that approximately 50 % of those infected clear within a year, 80 % within two years, and 90 % within three years.

The starved chlamydiae enter a persistent growth state wherein they stop cell division and become morphologically aberrant by increasing in size. Persistent organisms remain viable as they are capable of returning to a normal growth state once conditions in the host cell improve.

Image: “Ultrastructure of chlamydial infection.” by Openi. Licence: CC BY 2.0

  Chlamydophila trachomatis Chlamydophila psittaci Chlamydophila pneumoniae
Host Human Birds (especially parrots, pigeons and budgies) Human
Diseases Serotypes A-C: Trachoma (a chronic recurrent disorder of the conjunctivae and cornea of the eye) Ornithosis/Psittacosis Respiratory infections
Serotypes D-K: sexually transmitted urogenital infections and infections of the conjunctiva, perinatal infections
Serotypes L1, L2, L3: Lymphogranuloma venereum

Epidemiology of Chlamydia

Globally, as of 2013, sexually transmitted chlamydia affects approximately 141 million people (3.1 % of the population). It is more common in women (3.8 %) than men (2.5 %). In 2013 it resulted in about 1,100 deaths down from 1,500 in 1990.

In the United States, about 1.4 million cases were reported in 2014. The CDC estimates that if one includes unreported cases there are about 2.8 million each year. It affects around 2 % of young people. Infections are most common among those between the ages of 15 and 25 and are more common in women than men. In 2013 infections resulted in about 1,100 deaths. Chlamydial infection is the most common bacterial sexually transmitted infection in the UK.

Chlamydia causes more than 250,000 cases of epididymitis in the U.S. each year. Chlamydia causes 250,000 to 500,000 cases of PID every year in the United States. Women infected with chlamydia are up to five times more likely to become infected with HIV if exposed.

Epidemiology of Chlamydophila trachomatis

  • 30—50 % of all sterility is caused by chlamydia.
  • 90 % of all sterility caused by tube closure are caused by infections with Chlamydophila trachomatis.
  • Every fourth woman infected with chlamydia is affected by subsequent sterility.
Bild: "This photomicrograph reveals McCoy cell monolayers with Chlamydia trachomatis inclusion bodies; Magnified 200X." von CDC/Dr. E. Arum; Dr. N. Jacobs. Lizenz: Gemeinfrei

Image: “This photomicrograph reveals McCoy cell monolayers with Chlamydia trachomatis inclusion bodies; Magnified 200X.” by CDC/Dr. E. Arum; Dr. N. Jacobs. Licence: Free

Chlamydophila trachomatis is one of the most common pathogens of sexually transmitted diseases worldwide. According to WHO (2001), 89 million new infections with genital chlamydia occur worldwide per year. In Germany, the incidence is annually at 300,000 new infections. Particularly affected are persons with frequently changing sexual partners and children of infected mothers.

In epidemiological studies using molecular biology methods, up to 13 % of the sexually active adolescent women were identified as infected in Germany. This infection rate varies regionally and decreases with increasing age and entry into a stable partnership relationship (source: Robert Koch institute).

In pregnant women, 2—3 % are populated with C. trachomatis. The infant is at risk of 50 % at birth.

The incidence of lymphogranuloma venereum has decreased worldwide, but this sexually transmitted infection is still endemic in Asia, Africa, South America and parts of the Caribbean.

Trachoma occurs almost exclusively in tropical countries under poor hygienic conditions. After cataract, trachoma is the second most common cause of blindness in the world.

Age group: Young adults (15-22 years)

Epidemiology of Chlamydophila psittaci

Risk groups are:

  • Bird owners
  • Animal keepers and vets
  • Employees in pet shops, poultry farms or slaughterhouses

The transmission takes place by direct contact or by inhalation of dust particles or feces. Human-to-human transmission has not yet been demonstrated.

Epidemiology of Chlamydophila pneumoniae

C. Pneumoniae is a very common worldwide cause of respiratory infections of humans. According to seroepidemiological investigations, the prevalence begins at the preschool age and is above 50 % for men and over 70 % for men in the 6th decade.

A high prevalence of seropositivity is to be expected: Everyone has probably contact with C. pneumoniae once in a lifetime. 5 -15 % of all outpatient acquired pneumonia are caused by C. pneumoniae.

Age group: 60-80 years

Etiology and Pathogenesis of Chlamydia

Etiology and pathogenesis of Chlamydophila trachomatis

Serotypes A-C: Infectious eye secret, contaminated hands, towels (smear infection), flies
Serotypes D-K: Sexually transmitted, perinatal
Serotypes L1-L3: Sexually transmitted, causes Lymphogranuloma venereum perinatal

The incubation period is approximately 1—3 weeks.

Etiology and pathogenesis of Chlamydophila psittaci

Psittaci is the only zoonotic human pathogen from the Chlamydiaceae family. The excitation sources are mainly birds (chickens, ducks, pigeons, exotic birds).

The transfer takes place by direct contact or by inhalation of dust particles or feces containing pathogens.

The pathogens are partly infectious even after drying out for up to 4 weeks. The incubation period of the ornithosis is about 1—4 weeks.

Etiology and pathogenesis of Chlamydophila pneumoniae

Pneumoniae is transmitted from person to person in an aerogenic pathway and by salivary contact.

The incubation time is estimated to be about 1-4 weeks.

Pneumoniae may remain persistent for a long time in the upper respiratory tract (It is likely that the infected person will infect others over a long period of time).

Clinical Findings of Chlamydia

Symptoms of Chlamydophila trachomatis infection

Urogenital chlamydia infection

Note: 80 % of urogenital chlamydial infections in women are symptomatic!

The pathogens can persist for years undetected in the body and possibly even become chronic.

Clinical manifestation of Chlamydophila trachomatis in men and women

Women Men
Note: If the ascending infections persist, this can lead to adhesions in the tubes. Tube adhesions are the most common cause of sterility in women, extrauterine pregnancy and chronic pelvic symptoms.

Lymphogranuloma venereum

Image: "Lymphogranuloma venereum: is caused by the invasive serovars L1, L2, or L3 of Chlamydia trachomatis. This young adult experienced the acute onset of tender, enlarged lymph nodes in both groins." by Herbert L. Fred, MD and Hendrik A. van Dijk. Licence: CC BY 2.0

Image: “Lymphogranuloma venereum: is caused by the invasive serotypes L1, L2, or L3 of Chlamydia trachomatis. This young adult experienced the acute onset of tender, enlarged lymph nodes in both groins.” by Herbert L. Fred, MD and Hendrik A. van Dijk. Licence: CC BY 2.0

Primary stage Herpetiform papules, ulcer, rapid scalp-free healing
Secondary stage Inguinal, painful lymphadenopathy (Bubo)
Tertiary stage Fibrotic transformation of the lymph nodes, inflammation with ulceration, obliteration of the lymphatics, edema of the genital/extremity (elephantiasis), fever, arthralgia, splenomegaly, erythema nodosum

Newborn chlamydiosis

The newborn chlamydiosis appears as conjunctivitis (60 %) or pneumonia (40 %).

Typical symptoms of inclusion body conjunctivitis are:

  • Purulent, mucopurulent, hemorrhagic inflammation of the conjunctiva
  • Eyelid edema
  • Follicular infiltration of the inner lid side
  • First on one, then on both sides
  • Mostly inconsequential healing

Typical symptoms of neonatal pneumonia are:

  • Tachypnea
  • Increased respiratory effort
  • Snorkeling breathing sounds
  • Refusal of food
  • In severe cases cyanosis


Image: "Clinical features of trachoma. (a) Active trachoma in a child, characterised by a mixed papillary (TI) and follicular response (TF). (b) Tarsal conjunctival scarring (TS). (c) Entropion and trichiasis (TT). (d) Blinding corneal opacification (CO) with entropion and trichiasis (TT)." by Openi. Licence: CC BY 2.5

Image: “Clinical features of trachoma. (a) Active trachoma in a child, characterised by a mixed papillary (TI) and follicular response (TF). (b) Tarsal conjunctival scarring (TS). (c) Entropion and trichiasis (TT). (d) Blinding corneal opacification (CO) with entropion and trichiasis (TT).” by Openi. Licence: CC BY 2.5

The follicular keratoconjunctivitis is caused by an initial infection in the child’s age. Repeated infections and, among others, bacterial superinfections lead to the formation of granulomas. The result of the granulomas is scarred shrinkages of the conjunctiva of the eyelids and entropion. In the course of time, the cornea changes and becomes turbid.

Symptoms and Clinical Findings of Chlamydophila psittaci infection

The typical symptoms of ornithosis include:

Symptoms of Chlamydophila pneumoniae infection

Frequently, the course of C. pneumoniae infections is asymptomatic.

  • Acute and chronic infections of the upper respiratory tract (pharyngitis, sinusitis, bronchitis)
  • Outpatient pneumonia
  • All symptoms of infection with C .psittaci can also occur in C. pneumoniae.

Complications of Chlamydia

Possible complications of chlamydia infection

C. trachomatis  C. psittaci  C. pneumoniae
Disorders of the arthritic circle: joint inflammation (knee, ankle joint, …) Myocarditis, pericarditis, endocarditis, thrombophlebitis, CNS involvement Carditis, meningoradiculitis, erythema nodosum, reactive arthritis

Diagnostics of Chlamydia

Smear for the determination of the chlamydial pathogens

The detection of the pathogen is carried out by taking a smear of:

  • Trachoma: Conjunctiva smear
  • Eye infection: Conjunctiva smear
  • Urogenital infections: cervical or vaginal smear, possibly urethral smear
  • Lymphogranuloma venereum: Lymph node aspirate, ulcer smear

The direct detection of chlamydial antigens is carried out by means of fluorescence-labeled antibodies or ELISA. An alternative is a PCR with high specificity and sensitivity.

Image: "Chlamydiae within Peripheral Blood Transfer Infection when Cultured in vitro on J774A.1 host cell monolayers." by Openi. Licence: CC BY 2.0

Image: “Chlamydiae within Peripheral Blood Transfer Infection when Cultured in vitro on J774A.1 host cell monolayers.” by Openi. Licence: CC BY 2.0

The pathogen is detected indirectly by serum antibody determinations. It must be specifically investigated for the appropriate species, i.e. Chlamydophila trachomatis, C. pneumoniae or C. psittaci. The diagnosis of genital chlamydial infections evolved rapidly from the 1990s through 2006. Nucleic acid amplification tests (NAAT), such as polymerase chain reaction (PCR), transcription-mediated amplification (TMA), and the DNA strand displacement amplification (SDA) now are the mainstays.

Differential Diagnosis of Chlamydia

Chlamydia infection — similar medical conditions

C. trachomatis C. psittaci C. pneumoniae
  • Gonococcal urethritis
  • Trichomonad mycoplasma urethritis – Inflammation of the urethra by mycoplasmas, bacteria type without the cell wall
  • Urethritis caused by several different bacteria or viruses (e.g., herpes simplex virus)


Pathogens that trigger atypical pneumonia:

As in C. psittaci

Therapy of Chlamydia

Antibiotic against chlamydia

The drugs of choice in chlamydia are antibiotics.

C. trachomatis C.  pneumoniae, C. psittaci
Tetracyclines (Doxycyclin) Tetracyclines (Doxycyclin)
  • Macrolides (erythromycin, clarithromycin)
  • Quinolones (e. g. levofloxacin, moxifloxacin)
  • Azithromycin (in uncomplicated genital infections single dose)
Macrolides (erythromycin, azithromycin)
Duration of treatment: at least 14 days Duration of treatment: 10—21 days
Note: Especially important in the treatment of Chlamydophila trachomatis is the co-treatment of the partner (always!) in order to avoid a constant re-infection (so-called “ping-pong effect”).

Prevention of Chlamydia

Prevention measures for Chlamydophila trachomatis

Prevention measures for Chlamydophila psittaci

  • Compulsory reporting: Compliance with the veterinary rules of disease control
  • Early-onset of diagnosis and therapy in case of suspicion

Notification requirement

Which chlamydia infection is notifiable?

  • Trachomatis
  • Psittaci
  • Pneumoniae

Review Questions

The correct answers can be found below the references.

1. At what age the chlamydia screening is covered by the statutory health insurance in certain cases?

  1. from 16
  2. from 18
  3. from 25
  4. from 30
  5. from 35

2. A young woman has a new boyfriend recently. Since she has been suffering from itching and pain in the vulva for a week, she is looking for her practiced gynecologist. The physician observes swollen lymph nodes and flat ulcers in the vulvar area. Upon asking, the patient states that she has not used any protection in sexual intercourse. What infection is the most likely?

  1. Chlamydia infection
  2. HPV infection
  3. Herpes simplex virus infection
  4. HIV infection
  5. Measles infection

3. Which statement about chlamydia is true?

  1. Chlamydia psittaci is notifiable
  2. Chlamydia pneumoniae is notifiable
  3. Chlamydia trachomatis is notifiable
  4. Chlamydia psittaci is not notifiable
  5. All Chlamydia groups are not notifiable
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One thought on “Chlamydia (Chlamydia Bacteria Infection) — Symptoms and Treatment

  • magdi selim

    Thank you, simple, easy and effective.