Background
Chlamydiae are obligate intracellular organisms from bacteria that now comprise 3 species. They include the following: Chlamydia trachomatis, Chlamydia psittaci, and Chlamydia pneumoniae.
C trachomatis, which is almost exclusively a human pathogen, includes the agents of classic trachoma (ie, serotypes A, B, Ba, C). It also includes the agents of inclusion conjunctivitis or paratrachoma (ie, serotypes D-K). The latter organisms infect the epithelium of mucoid surfaces and were once identified as the trachoma-inclusion conjunctivitis agents (TRIC). Serotypes L1, L2, and L3, the agents that infect tissues deeper to the epithelium and cause lymphogranuloma venereum, also are included. [1]
C trachomatis is the most common cause of chronic follicular conjunctivitis (ie, follicular conjunctivitis lasting for >16-28 d). The organism also causes 3 clinical syndromes, which include the following: trachoma, adult inclusion conjunctivitis, and neonatal conjunctivitis. Trachoma and neonatal conjunctivitis are discussed in other chapters so this discussion is restricted to adult inclusion conjunctivitis. [1]
Adult inclusion conjunctivitis results from C trachomatis serotypes D-K, causing chronic follicular conjunctivitis that can occur in adults or in the neonate. The adult disease is transmitted sexually or from hand-to-eye contact. Gonorrhea is the most common co-infection with adult inclusion conjunctivitis. Rarely, the adult disease is transmitted from eye-to-eye contact (eg, sharing mascara). [1, 2]

Also see the Medscape Reference article Chlamydial Genitourinary Infections.
Pathophysiology
The epidemiology of this disease revolves around sexual contact. Modes of transmission include orogenital activities, hand-to-eye spread of infective genital secretions, and even direct ejaculate into the eye. [3] Although rare, eye-to-eye contact spread has been reported (eg, sharing mascara). The incubation period is 4-12 days.
Epidemiology
Frequency
United States
It is estimated that 1 in 300 patients who have genital chlamydial disease develop adult inclusion conjunctivitis.
Sex
No difference in frequency of disease between the sexes has been reported.
Age
Usually, this condition is observed in the young sexually active population. It is most common in persons aged 15-35 years.
Prognosis
Prognosis is excellent with treatment.
Patient Education
Educate patients about the risks of sexually transmitted diseases and safe sexual practices.
For patient education resources, see the Sexually Transmitted Diseases Center, as well as Sexually Transmitted Diseases and Chlamydia.
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This image reveals a close view of a patient's left eye with the upper lid retracted in order to reveal the inflamed conjunctival membrane lining the inside of both the upper and lower lids, due to what was determined to be a case of inclusion conjunctivitis, a type of conjunctival inflammation caused by the bacterium, Chlamydia trachomatis. Inclusion conjunctivitis, also known as chlamydial conjunctivitis, is more common in newborns. Symptoms include redness of the eye(s), swelling of the eyelids, and discharge of pus, usually 5 to 12 days after birth. Image courtesy of Susan Lindsley, Centers for Disease Control and Prevention.