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Chlamydial infections 

Chlamydial infections

Chlamydial infections

David Taylor-Robinson

and David Mabey


May 30, 2013: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.


Prevention of trachoma.

Conflicting evidence for C. trachomatis being involved in preterm birth.

Effectiveness of azithromycin questioned.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 28 April 2017

Chlamydiae are pathogenic bacteria that probably evolved from host-independent, Gram-negative ancestors and are specialized for an intracellular existence. The chlamydial infectious elementary body binds to and enters the host cell by ‘parasite-specified’ endocytosis, with a new generation of elementary bodies being released 30 to 48 h later.

There are nine species of genus Chlamydia (which some would reclassify based on ribosomal sequence data into two genera, Chlamydia and Chlamydophila), of which C. trachomatis and C. pneumoniae are primarily human pathogens, and C. psittaci, C. abortus, and C. felis are species transmitted occasionally from animals.


Caused by C. trachomatis serovars A, B, Ba, and C. A disease of poor rural communities, mainly in Africa and Asia, where the reservoir of infection is the eye (and possibly nasopharynx) of children with active disease, with transmission from the eye of one individual to that of another via fingers, fomites, coughing and sneezing, and by eye-seeking flies.

Clinical features and diagnosis—the active (inflammatory) stage is a follicular conjunctivitis with characteristic subconjunctival follicles that are usually seen in children in endemic areas. Repeated infections lead to conjunctival scarring, with turned-in lashes rubbing against the cornea (trichiasis) and eventually causing severe damage (3.6% of global blindness, or 1.3 million cases). In endemic areas diagnosis is made on clinical grounds.

Treatment and prevention—inflammatory trachoma responds to either an appropriate course of 1% topical tetracycline ointment or a single oral dose of azithromycin. Community-based mass treatment is recommended when there is high prevalence of disease in children aged 1 to 9 years. Trichiasis requires surgical correction. A World Health Organization initiative to eliminate blinding trachoma by 2020 is based on the acronym ‘SAFE’: Surgery for trichiasis; Antibiotics for treatment; Face washing; Environmental improvement to reduce fly populations that transmit the organisms.

Genital tract infections

These are caused by C. trachomatis serovars D to K, which exist worldwide. In men they cause up to 50% of symptomatic nongonococcal urethritis and of acute epididymitis. In women they cause up to 50% of (mostly asymptomatic) urethritis and of (often asymptomatic) cervicitis; further spread leads to endometritis, salpingitis and (occasionally) perihepatitis, and infertility follows a single upper genital tract infection in about 10% of women. See Chapter 8.5 for further discussion.

Other diseases caused by C. trachomatis

These include: (1) Adult paratrachoma and otitis media. (2) Reactive arthritisat least one-third of sexually acquired reactive arthritis is initiated by genital C. trachomatis infection (see Chapter 19.8). (3) Neonatal infection—babies exposed to serovars D to K at birth often develop conjunctivitis, and some develop pneumonia. (4) Lymphogranuloma venereum—caused by C. trachomatis serovars L1, L2 or L3. Endemic in parts of Africa, Asia, South America, and the Caribbean; 2003 saw the start of an outbreak (serovar L2) across western Europe, the United Kingdom, North America, and Australia in homosexual men who were mainly HIV-positive. The clinical course comprises three stages: (a) primary—a small painless papule occurs at the site of inoculation; followed some weeks later by (b) secondary—inguinal and/or femoral lymphadenopathy with systemic features; anorectal involvement is usually seen in homosexual men; sometimes progressing to (c) tertiary—severe fibrosis, which is rarely seen because of earlier broad-spectrum antibiotic therapy. Diagnosis depends on serology or on identification of the organism in appropriate clinical samples. Treatment is usually with doxycycline or erythromycin.

Other chlamydiae

C. pneumoniae—transmitted directly from person to person by droplet spread and causes respiratory disease (pharyngitis, bronchitis, pneumonia), is a possible trigger for reactive arthritis and for some cases of juvenile chronic arthritis, and its DNA has been detected in atheromatous arteries, but without definite evidence that it contributes to heart disease. See Chapter 18.4.2 for further discussion.

C. psittaci—transmitted from psittacine birds and causes psittacosis, which can range from a mild influenza-like illness to a fulminating toxic state with multiorgan involvement.

C. abortus—causes abortion in sheep and may do so in pregnant women exposed to infected animals during the lambing season.

Diagnosis and treatment

Diagnosis—depends on (1) culture—chlamydiae can be grown in cultured cells, but this is slow, labour intensive, and less sensitive than molecular methods; (2) antigen detection—enzyme immunoassays are easy to use, but insensitive; (3) nucleic acid detection—the ‘gold standard’ for routine diagnosis, screening, and for research into chronic or persistent disease; and—to a much lesser extent—(4) serology.

Treatment—chlamydiae are particularly sensitive to tetracyclines (e.g. doxycycline) and macrolides (e.g. erythromycin, and with azithromycin gaining popularity because it can be effective as a single dose: however, there is debate as to whether it is the most efficacious antibiotic).

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