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Medicine – Chlamydial Infection: Aetiology, Transmission, Pathogenesis, Clinical Features, Diagnosis and Treatment
1. Introduction to Chlamydial Infection
Chlamydial infection is a common sexually transmitted infection (STI) caused by Chlamydia trachomatis, an obligate intracellular bacterium that primarily infects epithelial cells of the genitourinary tract.
It is one of the most important causes of non-gonococcal urethritis (NGU) in men and cervicitis and pelvic inflammatory disease (PID) in women.
An important feature of chlamydial infection is that many infected individuals remain asymptomatic. Despite the absence of symptoms, the organism can persist, cause inflammation and produce complications.
In women, untreated infection may ascend from the cervix into the upper genital tract, causing salpingitis, pelvic inflammatory disease, tubal damage, ectopic pregnancy and infertility.
Chlamydia may also be transmitted from an infected mother to her infant during childbirth, causing neonatal conjunctivitis or pneumonia.
The infection is treatable with antibiotics, particularly doxycycline, although treatment selection depends on pregnancy status, age and the clinical syndrome.
2. Aetiological Agent – Chlamydia trachomatis
The causative organism is Chlamydia trachomatis, a small, Gram-negative-like bacterium belonging to the family Chlamydiaceae.
Unlike most bacteria, Chlamydia trachomatis cannot complete its reproductive cycle independently outside a host cell.
It is therefore described as an obligate intracellular bacterium.
The organism preferentially infects columnar epithelial cells lining the cervix, urethra, rectum and conjunctiva.
Different serovars of Chlamydia trachomatis are associated with different clinical syndromes, including sexually transmitted infections, trachoma and lymphogranuloma venereum.
3. Classification of Chlamydia trachomatis Serovars
Chlamydia trachomatis is classified into serovars according to antigenic differences.
Serovars A, B, Ba and C are associated with trachoma, a chronic ocular infection that can cause conjunctival scarring and blindness.
Serovars D–K are responsible for most sexually transmitted urogenital chlamydial infections.
These serovars may also cause neonatal conjunctivitis and pneumonia following exposure during childbirth.
Serovars L1, L2 and L3 cause lymphogranuloma venereum (LGV), a more invasive sexually transmitted infection that can produce lymphadenopathy and proctocolitis.
This classification is important because the clinical manifestations and treatment durations may differ.
Microbiology and Pathogenesis
4. Obligate Intracellular Nature
Chlamydia trachomatis requires living host cells for replication.
It cannot reproduce using the same extracellular mechanisms as many conventional bacteria.
The organism has a distinctive developmental cycle involving two principal forms: the elementary body and the reticulate body.
These forms perform different functions during infection.
The elementary body is adapted for transmission and entry into host cells, whereas the reticulate body is adapted for intracellular replication.
5. Elementary Body
The elementary body (EB) is the small, infectious extracellular form of Chlamydia trachomatis.
It is metabolically relatively inactive and structurally adapted to survive outside host cells for a limited period.
The elementary body attaches to susceptible epithelial cells and enters through an endocytic process.
Once inside the host cell, it begins transforming into the reticulate body.
The elementary body is therefore responsible for initiating infection.
6. Reticulate Body
The reticulate body (RB) is the larger, metabolically active, non-infectious intracellular form.
After transformation from the elementary body, the reticulate body replicates within a membrane-bound intracellular inclusion.
Replication occurs by binary fission.
Following multiplication, reticulate bodies differentiate back into elementary bodies.
The newly formed elementary bodies are subsequently released and infect neighbouring epithelial cells.
This cycle contributes to the spread of infection and the development of local inflammation.
7. Pathogenesis of Tissue Injury
Chlamydial infection causes tissue injury through direct effects on infected epithelial cells and the host inflammatory response.
The organism replicates within epithelial cells and stimulates the release of inflammatory mediators.
These mediators recruit immune cells to the infected tissues.
Persistent or repeated inflammation can produce epithelial damage, fibrosis and scarring.
In the female reproductive tract, scarring of the fallopian tubes is particularly important because it may impair fertility.
Therefore, the major complications of chlamydial infection often result from inflammation and subsequent tissue damage, rather than simply the presence of the organism.
Transmission of Chlamydial Infection
8. Sexual Transmission
Chlamydia trachomatis is transmitted predominantly through sexual contact.
Transmission may occur during vaginal, anal or oral sexual activity.
The organism infects susceptible mucosal surfaces, particularly those lined by columnar epithelium.
Infection may involve the cervix, urethra, rectum or pharynx.
Transmission can occur even when the infected individual has no symptoms.
This is clinically important because asymptomatic infection contributes substantially to the continued spread of chlamydia.
9. Vertical Transmission
Chlamydia may be transmitted from an infected mother to her infant during childbirth.
The infant becomes exposed to infected genital secretions during passage through the birth canal.
This can lead to infection of the neonatal conjunctiva or respiratory tract.
The two classical neonatal manifestations are inclusion conjunctivitis and afebrile pneumonia.
Appropriate maternal screening and treatment during pregnancy reduce the risk of neonatal infection.
10. Incubation Period
The incubation period of symptomatic urogenital chlamydial infection is commonly approximately 1–3 weeks.
However, many infections remain asymptomatic.
Symptoms may develop gradually and may be mild.
Because the timing of symptom onset is variable, it is often difficult to determine exactly when infection was acquired.
Untreated infection may persist for prolonged periods.
Chlamydial Infection in Men
11. Non-Gonococcal Urethritis
Chlamydia is a major cause of non-gonococcal urethritis (NGU), historically also called non-specific urethritis (NSU).
Urethritis refers to inflammation of the urethral mucosa.
The original notes state that Chlamydia trachomatis is responsible for more than 50% of cases of non-specific urethritis.
This is a traditional teaching association, but the proportion varies considerably between populations.
Modern estimates generally attribute approximately 15–40% of NGU cases to Chlamydia trachomatis, rather than consistently more than 50%.
Other causes include Mycoplasma genitalium, Trichomonas vaginalis and certain viral infections.
12. Clinical Features of Chlamydial Urethritis
Chlamydial urethritis may produce dysuria, urethral irritation and urethral discharge.
The discharge is often scanty, clear or mucoid, although it may occasionally be mucopurulent.
Patients may complain of burning during urination or discomfort at the urethral opening.
Symptoms are often milder than those associated with gonococcal urethritis.
However, the clinical features overlap, and the two infections cannot be reliably distinguished by symptoms alone.
13. Asymptomatic Urethral Infection
Many men with urethral chlamydial infection have no noticeable symptoms.
Despite the absence of symptoms, infection may persist within the urethral epithelium.
Asymptomatic individuals can transmit the organism to sexual partners.
This is one reason chlamydia remains common despite the availability of effective antibiotic treatment.
14. Epididymitis
Chlamydia may ascend from the urethra into the epididymis, causing epididymitis.
The epididymis is a coiled tubular structure located behind the testis that is involved in sperm maturation and transport.
Patients may develop unilateral scrotal pain, swelling and tenderness.
Dysuria or urethral discharge may also be present.
In sexually active younger men, Chlamydia trachomatis and Neisseria gonorrhoeae are important causes of epididymitis.
Acute severe testicular pain requires urgent assessment to exclude testicular torsion.
15. Reactive Arthritis
Chlamydial infection may trigger reactive arthritis.
Reactive arthritis is an inflammatory joint disorder that develops following certain gastrointestinal or genitourinary infections.
The arthritis is sterile, meaning that viable organisms are generally not present within the affected joint.
Patients may develop asymmetric oligoarthritis, commonly involving the knees, ankles or feet.
Enthesitis, dactylitis and inflammatory back pain may also occur.
Some patients develop conjunctivitis or uveitis.
The classical association is urethritis, arthritis and conjunctivitis, although the complete triad is not always present.
Chlamydial Infection in Women
16. Cervicitis
Chlamydia commonly infects the columnar epithelial cells of the endocervix.
This may produce cervicitis, which is inflammation of the cervix.
Patients may develop abnormal vaginal discharge, intermenstrual bleeding or postcoital bleeding.
On examination, the cervix may appear inflamed or friable.
Mucopurulent discharge may be visible at the cervical opening.
However, many women with cervical chlamydial infection remain asymptomatic.
17. Clinical Features of Chlamydial Cervicitis
Symptomatic cervicitis may produce increased vaginal discharge, pelvic discomfort or bleeding after sexual intercourse.
The discharge may be mucopurulent because of inflammatory cells and cervical secretions.
Dysuria may occur if the urethra is also infected.
Cervical friability can cause contact bleeding during examination.
These findings are not specific to chlamydia because gonorrhoea and other infections may produce similar manifestations.
18. Ascending Genital Tract Infection
Untreated cervical infection may ascend into the upper female reproductive tract.
The organism can spread from the cervix into the endometrium and fallopian tubes.
This may produce endometritis and salpingitis.
The resulting inflammation can damage the reproductive tract.
In some patients, this progresses to pelvic inflammatory disease.
Ascending infection is clinically important because it may cause permanent reproductive complications even when the initial cervical infection was mild or asymptomatic.
Pelvic Inflammatory Disease
19. Introduction to Pelvic Inflammatory Disease
Pelvic inflammatory disease (PID) refers to infection and inflammation involving the upper female genital tract.
It may include endometritis, salpingitis, tubo-ovarian abscess and pelvic peritonitis.
Chlamydia trachomatis is an important cause of PID.
Neisseria gonorrhoeae and other organisms, including vaginal anaerobes, may also contribute.
PID is frequently polymicrobial.
The major concern is that inflammation may damage the fallopian tubes and surrounding pelvic structures.
20. Clinical Features of PID
Patients with PID commonly present with lower abdominal or pelvic pain.
Other symptoms may include abnormal vaginal discharge, fever, dyspareunia, intermenstrual bleeding or postcoital bleeding.
On pelvic examination, cervical motion tenderness, uterine tenderness or adnexal tenderness may be present.
However, PID may produce mild or non-specific symptoms.
Some patients develop significant upper genital tract inflammation without recognising that they have an infection.
21. Salpingitis
Salpingitis is inflammation of the fallopian tubes.
It commonly develops when organisms ascend from the cervix into the upper genital tract.
Chlamydial infection can produce inflammation of the tubal epithelium.
Persistent inflammation may damage ciliated epithelial cells and cause fibrosis.
This can interfere with the transport of the ovum through the fallopian tube.
The resulting tubal damage is a major mechanism of chlamydia-associated infertility and ectopic pregnancy.
22. Tubal Infertility
Untreated chlamydial infection can cause infertility through damage to the fallopian tubes.
Inflammation may produce scarring, adhesions and partial or complete tubal obstruction.
Normally, the fallopian tubes transport the ovum and provide the usual site of fertilisation.
When the tubes become obstructed or damaged, sperm and ova may be unable to meet.
This reduces the likelihood of natural conception.
Chlamydia is therefore an important preventable cause of tubal-factor infertility.
The risk increases with repeated or severe episodes of upper genital tract infection.
23. Ectopic Pregnancy
Chlamydial salpingitis increases the risk of ectopic pregnancy.
An ectopic pregnancy occurs when implantation takes place outside the uterine cavity.
The most common location is the fallopian tube.
Tubal inflammation and scarring may impair transport of the fertilised ovum.
This increases the likelihood of implantation within the tube.
A ruptured ectopic pregnancy can cause life-threatening intra-abdominal haemorrhage.
Therefore, ectopic pregnancy must be considered in a patient of reproductive potential presenting with pelvic pain and a positive pregnancy test.
24. Chronic Pelvic Pain
PID may result in chronic pelvic pain.
Persistent discomfort can arise from inflammation, pelvic adhesions or damage to reproductive structures.
The pain may continue even after the original infection has been successfully treated.
This occurs because antibiotics eliminate susceptible organisms but cannot necessarily reverse established tissue scarring.
Early recognition and treatment of chlamydial infection are therefore important for preventing long-term complications.
25. Fitz-Hugh–Curtis Syndrome
Fitz-Hugh–Curtis syndrome is perihepatitis associated with pelvic inflammatory disease.
It involves inflammation of the liver capsule rather than primary infection of the liver parenchyma.
Patients may develop right upper quadrant abdominal pain, sometimes resembling gallbladder disease.
Laparoscopy may reveal characteristic thin adhesions between the liver capsule and abdominal wall.
These are classically described as violin-string adhesions.
Both Chlamydia trachomatis and Neisseria gonorrhoeae may be associated with this syndrome.
Neonatal Chlamydial Infection
26. Introduction to Neonatal Chlamydia
Neonatal chlamydial infection usually results from exposure to maternal genital infection during childbirth.
The organism may infect the conjunctiva or respiratory tract.
The two important manifestations are neonatal inclusion conjunctivitis and chlamydial pneumonia.
Both conditions are associated mainly with Chlamydia trachomatis serovars D–K.
27. Neonatal Inclusion Conjunctivitis
Neonatal inclusion conjunctivitis is an ocular infection caused by Chlamydia trachomatis.
It typically develops approximately 5–12 days after birth.
The infant may develop conjunctival redness, eyelid swelling and mucopurulent ocular discharge.
The infection can affect one or both eyes.
Because the organism may also be present in the respiratory tract, systemic antibiotic treatment is necessary.
Topical eye treatment alone is insufficient.
28. Chlamydial Pneumonia in Neonates
Chlamydial pneumonia is another recognised manifestation of perinatally acquired infection.
It typically develops between 1 and 3 months of age.
The illness is often gradual in onset.
Infants may develop tachypnoea and a characteristic repetitive, staccato cough.
Fever is usually absent.
This presentation is commonly described as afebrile pneumonia of infancy.
29. Clinical Features of Neonatal Chlamydial Pneumonia
Infants with chlamydial pneumonia may present with persistent cough, rapid breathing and feeding difficulties.
The cough may have a characteristic staccato pattern, consisting of short, repetitive bursts.
Chest imaging may demonstrate bilateral diffuse interstitial infiltrates or hyperinflation.
Peripheral blood eosinophilia may also occur.
The infection generally develops gradually rather than producing the abrupt severe illness associated with some bacterial pneumonias.
30. Treatment of Neonatal Chlamydial Infection
Neonatal chlamydial conjunctivitis and pneumonia require systemic antibiotic treatment.
Oral erythromycin is a recognised treatment option.
Azithromycin may also be used in selected circumstances.
Treatment choice depends on age, clinical presentation and applicable paediatric guidance.
Macrolide treatment in young infants is associated with a risk of infantile hypertrophic pyloric stenosis, particularly during early infancy.
Therefore, treated infants should be monitored appropriately.
Other Clinical Manifestations of Chlamydia trachomatis
31. Trachoma
Trachoma is a chronic ocular infection caused by Chlamydia trachomatis serovars A, B, Ba and C.
It is transmitted through contact with infected ocular or nasal secretions, including through contaminated hands and certain flies.
Repeated infection produces chronic conjunctival inflammation.
Over time, conjunctival scarring may cause the eyelashes to turn inward, a condition called trichiasis.
The eyelashes may damage the cornea, eventually causing corneal opacity and blindness.
Trachoma is an important preventable cause of infectious blindness worldwide.
32. Lymphogranuloma Venereum
Lymphogranuloma venereum (LGV) is caused by Chlamydia trachomatis serovars L1, L2 and L3.
Unlike the more superficial infections caused by serovars D–K, LGV is relatively invasive and may involve lymphatic tissues.
The initial lesion may be a small, transient genital ulcer that goes unnoticed.
Subsequently, patients may develop painful regional lymphadenopathy.
Inguinal lymph nodes may become enlarged and form buboes.
LGV may also produce severe proctocolitis, particularly following rectal exposure.
33. Treatment of Lymphogranuloma Venereum
LGV requires a longer antibiotic course than uncomplicated urogenital chlamydial infection.
The standard adult regimen is doxycycline 100 mg orally twice daily for 21 days.
This prolonged course is used because LGV is more invasive and may involve deeper tissues and lymphatic structures.
Patients with severe complications may require additional assessment and management.
Diagnosis of Chlamydial Infection
34. Clinical Suspicion
Chlamydial infection should be considered in sexually active patients presenting with urethritis, cervicitis, pelvic pain or compatible complications.
However, clinical findings alone are insufficient for diagnosis.
Many infected individuals are asymptomatic.
Furthermore, chlamydia and gonorrhoea can produce similar symptoms and may occur together.
Laboratory testing is therefore essential for accurate diagnosis.
35. Nucleic Acid Amplification Testing
Nucleic acid amplification testing (NAAT) is the preferred diagnostic method for Chlamydia trachomatis infection.
NAAT detects chlamydial genetic material.
It offers high sensitivity and specificity.
Depending on the anatomical site and assay, suitable specimens include first-catch urine, vaginal swabs, cervical swabs and rectal swabs.
Pharyngeal specimens may also be tested when appropriate.
NAAT has largely replaced older diagnostic methods for routine urogenital chlamydial infection.
36. Specimen Collection
In men, first-catch urine is commonly used for detecting urethral chlamydial infection.
In women, vaginal swabs are generally preferred because they provide excellent diagnostic sensitivity.
Self-collected vaginal swabs can be suitable when supported by the test and clinical service.
Rectal swabs may be necessary when rectal infection is suspected or screening is indicated.
The appropriate specimen depends on the patient’s anatomy, exposure history and symptoms.
37. Chlamydia and Gonorrhoea Testing
Patients with suspected chlamydial infection are commonly tested for gonorrhoea at the same time.
This is because both organisms may cause urethritis and cervicitis.
Coinfection can occur.
Many modern molecular assays detect both Chlamydia trachomatis and Neisseria gonorrhoeae from the same specimen.
Identifying both infections is important because treatment regimens differ.
Treatment of Chlamydial Infection
38. Doxycycline
Doxycycline is the preferred treatment for uncomplicated chlamydial infection in non-pregnant adults and adolescents.
It belongs to the tetracycline class of antibiotics.
Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
This prevents aminoacyl-tRNA from attaching normally to the ribosome.
As a result, bacterial protein synthesis is inhibited.
Doxycycline is generally bacteriostatic.
39. Recommended Doxycycline Regimen
The commonly recommended adult regimen for uncomplicated urogenital chlamydial infection is:
Doxycycline 100 mg orally twice daily for seven days.
This regimen is effective for uncomplicated urethral, cervical and rectal chlamydial infection.
Doxycycline is particularly preferred for rectal infection because it has demonstrated better efficacy than single-dose azithromycin in relevant studies.
Patients should complete the prescribed course.
40. Erythromycin
Erythromycin is a macrolide antibiotic with activity against Chlamydia trachomatis.
It inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit.
This interferes with protein elongation.
The original notes correctly identify erythromycin as an antibiotic with activity against chlamydia.
However, erythromycin is no longer a preferred routine treatment for uncomplicated adult chlamydial infection because gastrointestinal adverse effects can reduce adherence and other regimens are generally better tolerated.
It remains relevant in selected situations, including some neonatal infections.
41. Azithromycin
Azithromycin is another macrolide antibiotic used in the treatment of chlamydial infection.
It binds to the 50S ribosomal subunit and inhibits bacterial protein synthesis.
A single oral dose of azithromycin 1 g is an alternative regimen for uncomplicated chlamydial infection in non-pregnant adults when doxycycline is unsuitable.
However, azithromycin is less effective than doxycycline for rectal chlamydial infection.
Therefore, doxycycline is generally preferred when appropriate.
42. Treatment During Pregnancy
Doxycycline is generally avoided during pregnancy, particularly in later pregnancy.
Azithromycin 1 g orally as a single dose is a recommended regimen for uncomplicated chlamydial infection during pregnancy.
Amoxicillin is an alternative in selected circumstances.
Pregnant patients should undergo appropriate follow-up testing because persistent infection can affect maternal and neonatal health.
A test of cure using NAAT is generally recommended approximately four weeks after treatment during pregnancy.
43. Treatment of Pelvic Inflammatory Disease
Chlamydia-associated PID requires broader antimicrobial treatment than uncomplicated cervical infection.
This is because PID may involve multiple organisms, including Neisseria gonorrhoeae and anaerobic bacteria.
A commonly recommended outpatient regimen includes ceftriaxone, doxycycline and metronidazole.
Doxycycline treats chlamydial infection, while ceftriaxone provides gonococcal coverage and metronidazole provides anaerobic coverage.
Severe PID, pregnancy, tubo-ovarian abscess or inability to tolerate oral treatment may require hospitalisation and intravenous antibiotics.
44. Treatment of Sexual Partners
Sexual partner management is essential to prevent reinfection.
Recent sexual partners should be assessed and treated according to applicable guidelines.
Patients should avoid sexual intercourse until they and their partners have completed appropriate treatment.
For a seven-day doxycycline regimen, this generally means abstaining until the course has been completed.
For single-dose treatment, patients should avoid sexual intercourse for seven days after treatment.
Reinfection is common when sexual partners remain untreated.
45. Follow-Up and Retesting
Routine test of cure is not generally necessary for non-pregnant patients with uncomplicated chlamydial infection who have completed appropriate treatment and have no persistent symptoms or concerns about adherence.
However, repeat testing is recommended approximately three months after treatment because reinfection is common.
Pregnant patients require a test of cure approximately four weeks after treatment.
NAAT should not be performed too soon after therapy because residual bacterial genetic material may produce a positive result even after successful treatment.
Complications of Chlamydial Infection
46. Female Infertility
Chlamydia may cause infertility through ascending infection and inflammation of the fallopian tubes.
Repeated or severe episodes of salpingitis increase the risk of tubal scarring.
This may impair ovum transport and fertilisation.
The resulting infertility may persist despite successful antibiotic treatment because established structural damage may be irreversible.
47. Ectopic Pregnancy
Tubal scarring following chlamydial infection increases the risk of ectopic pregnancy.
Impaired transport of the fertilised ovum may lead to implantation within the fallopian tube.
Tubal ectopic pregnancy can rupture and cause severe internal bleeding.
Early recognition of pregnancy-related pelvic pain is therefore important.
48. Chronic Pelvic Pain
Chlamydia-associated PID may result in persistent pelvic pain.
This may arise from adhesions, chronic inflammation or structural damage.
Pain can persist even after the original infection has been eradicated.
49. Neonatal Conjunctivitis
Maternal chlamydial infection may be transmitted during childbirth.
The infant may develop conjunctivitis approximately 5–12 days after birth.
Symptoms include conjunctival redness, eyelid swelling and mucopurulent discharge.
Systemic antibiotic treatment is required.
50. Neonatal Pneumonia
Neonatal chlamydial pneumonia typically develops between one and three months of age.
It classically produces an afebrile illness with a staccato cough and tachypnoea.
Chest imaging may demonstrate diffuse interstitial changes.
Prevention of Chlamydial Infection
51. Safer Sexual Practices
Chlamydial infection can be prevented by reducing exposure to infected genital secretions.
Consistent and correct condom use reduces the risk of transmission.
However, no barrier method provides complete protection against all sexually transmitted infections.
Avoiding sexual contact until treatment is completed is important in preventing reinfection.
52. Screening
Because chlamydial infection is frequently asymptomatic, screening is an important preventive strategy.
Screening recommendations vary according to age, sexual exposure, pregnancy status and local guidelines.
Sexually active younger women and other individuals at increased risk are commonly prioritised for screening.
Early detection and treatment can reduce transmission and prevent reproductive complications.
53. Antenatal Screening
Chlamydia screening during pregnancy helps identify maternal infection before delivery.
Appropriate antibiotic treatment reduces the risk of neonatal conjunctivitis and pneumonia.
Pregnant patients may require repeat testing according to risk factors and local recommendations.
Differential Diagnosis of Urethritis
54. Chlamydial Urethritis
Chlamydial urethritis is caused by Chlamydia trachomatis.
It commonly produces mild dysuria and scanty mucoid or mucopurulent urethral discharge.
Many patients are asymptomatic.
Diagnosis is established using NAAT.
Treatment generally involves doxycycline.
55. Gonococcal Urethritis
Gonococcal urethritis is caused by Neisseria gonorrhoeae.
It classically produces more prominent purulent urethral discharge and dysuria.
However, symptoms overlap with chlamydial urethritis.
Diagnosis is usually established using NAAT, with culture and susceptibility testing in selected circumstances.
Treatment commonly involves ceftriaxone.
56. Mycoplasma genitalium Urethritis
Mycoplasma genitalium is another important cause of non-gonococcal urethritis.
It may produce persistent or recurrent urethral symptoms.
The organism lacks a cell wall, making beta-lactam antibiotics ineffective.
Treatment is complicated by increasing antimicrobial resistance.
Resistance-guided therapy is preferred when available.
Important Corrections and Clarifications
57. Proportion of Non-Specific Urethritis Caused by Chlamydia
The original notes state that chlamydia causes more than 50% of cases of non-specific urethritis.
Although chlamydia is a major cause of NGU, this proportion is not consistently supported by modern epidemiological data.
The proportion varies by population, with estimates commonly around 15–40%.
Other organisms, particularly Mycoplasma genitalium, are also important causes.
58. Association with PID and Infertility
The original notes correctly identify chlamydia as an important cause of PID and infertility.
The main mechanism involves ascending infection, salpingitis and subsequent fallopian tube scarring.
This can lead to tubal infertility, ectopic pregnancy and chronic pelvic pain.
59. Neonatal Infection
The original notes correctly identify neonatal conjunctivitis and diffuse pneumonia as complications.
Chlamydial conjunctivitis typically develops within the first two weeks of life.
Chlamydial pneumonia usually develops between one and three months of age.
The pneumonia is classically afebrile and associated with a staccato cough.
60. Antibiotic Sensitivity
The original notes identify doxycycline and erythromycin as active against chlamydia.
Both have antimicrobial activity.
However, doxycycline is now preferred for uncomplicated chlamydial infection in non-pregnant adults.
Azithromycin is recommended during pregnancy, while erythromycin remains relevant in selected circumstances, particularly neonatal treatment.
Important Clinical Associations – Note Form
61. Chlamydia trachomatis
Chlamydia trachomatis is an obligate intracellular bacterium.
It infects epithelial cells of the genitourinary tract, conjunctiva and other mucosal surfaces.
It has a distinctive developmental cycle involving elementary and reticulate bodies.
62. Elementary Body
The elementary body is the infectious extracellular form.
It attaches to and enters susceptible host cells.
63. Reticulate Body
The reticulate body is the metabolically active intracellular replicative form.
It multiplies within membrane-bound inclusions.
64. Non-Gonococcal Urethritis
Chlamydia is a major cause of non-gonococcal urethritis.
Patients may develop dysuria and scanty urethral discharge.
Many infections are asymptomatic.
65. Pelvic Inflammatory Disease
Chlamydia may ascend from the cervix into the upper genital tract.
This can cause endometritis, salpingitis and PID.
66. Tubal Infertility
Repeated or severe chlamydial salpingitis may produce fallopian tube scarring.
This can impair fertilisation and increase the risk of infertility.
67. Ectopic Pregnancy
Tubal damage may interfere with normal transport of the fertilised ovum.
This increases the risk of implantation within the fallopian tube.
68. Neonatal Conjunctivitis
Chlamydial conjunctivitis typically develops 5–12 days after birth.
It produces conjunctival inflammation and mucopurulent discharge.
69. Neonatal Pneumonia
Chlamydial pneumonia typically develops at 1–3 months of age.
It is classically afebrile and associated with a staccato cough.
70. Doxycycline
Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
It is the preferred treatment for uncomplicated chlamydial infection in non-pregnant adults.
71. Erythromycin
Erythromycin is a macrolide antibiotic that inhibits the 50S ribosomal subunit.
It is active against chlamydia but is no longer preferred for routine uncomplicated adult infection.
It remains useful in selected neonatal infections.
72. Azithromycin
Azithromycin is a macrolide antibiotic.
It is a recommended treatment for chlamydial infection during pregnancy.
It may also be used as an alternative in selected non-pregnant patients.
Key Clinical Pattern
The defining characteristic of chlamydial infection is its ability to cause frequently asymptomatic genital infection that may progress to urethritis, cervicitis, PID and infertility, or be transmitted to neonates during childbirth.
Chlamydia trachomatis → Obligate intracellular bacterium.
Elementary body → Infectious extracellular form.
Reticulate body → Intracellular replicative form.
Serovars D–K → Urogenital infection, neonatal conjunctivitis and neonatal pneumonia.
Serovars A–C → Trachoma.
Serovars L1–L3 → Lymphogranuloma venereum.
Men → Non-gonococcal urethritis, often with mild discharge and dysuria.
Women → Cervicitis and ascending pelvic inflammatory disease.
PID → Salpingitis, tubal damage, infertility and ectopic pregnancy.
Neonatal conjunctivitis → Develops approximately 5–12 days after birth.
Neonatal pneumonia → Afebrile pneumonia with staccato cough at 1–3 months of age.
Reactive arthritis → May follow chlamydial genitourinary infection.
Fitz-Hugh–Curtis syndrome → Perihepatitis associated with PID.
NAAT → Preferred diagnostic test.
Doxycycline → First-line treatment in non-pregnant adults.
Azithromycin → Recommended treatment during pregnancy.
Erythromycin → Active against chlamydia and used in selected neonatal infections.
Partner treatment → Important for preventing reinfection.
For examinations, remember the classical association: Chlamydia trachomatis causes non-gonococcal urethritis in men, pelvic inflammatory disease and tubal infertility in women, and conjunctivitis or afebrile staccato-cough pneumonia in neonates. Doxycycline is the preferred treatment for uncomplicated infection in non-pregnant adults.
