Trachoma

What is trachoma?¹

Trachoma is a very common chronic conjunctival infection caused by Chlamydia trachomatis, which is transmitted by flies or through close personal contact. (Note that the organism involved is C. trachomatis serotype A-C; C. trachomatis serotypes D-K are associated with genital infections and only occasionally cause a chronic follicular conjunctivitis that is clinically indistinguishable from trachoma).

An individual’s immune system can clear a single episode of infection, but in endemic communities re-acquisition of the organism occurs frequently.

Repeated episodes of infection cause chronic follicular conjunctival inflammation (active trachoma), leading on to the cicatricial stage of tarsal conjunctival scarring, entropion, trichiasis (in-turning of the eyelashes) which leads to corneal scarring and opacity.

Irreversible opacities result in visual impairment or blindness. The age at which this occurs depends on several factors including local transmission intensity. In very highly endemic communities it can occur in childhood, though onset of visual impairment between the ages of 30 and 40 years is more typical.

How common is trachoma? (Epidemiology)¹

Trachoma is a public health problem in 42 countries, and is responsible for the blindness or visual impairment of about 1.9 million people.

Trachoma is hyperendemic in many of the poorest and most rural areas of Africa, Central and South America, Asia, Australia and the Middle East. Overall, Africa remains the most affected continent.

Blindness from trachoma is irreversible. Based on June 2022 data, 125 million people live in trachoma endemic areas and are at risk of trachoma blindness.

In 2021, 69,266 people received surgical treatment for advanced stage of the disease, and 64.6 million people were treated with antibiotics. Global antibiotic coverage in 2021 was 44%.

In areas where trachoma is endemic, active (inflammatory) trachoma is common among preschool-aged children, with prevalence rates which can be as high as 60–90%.

Pathophysiology^{1 2}

Infection becomes less frequent and shorter in duration with increasing age. Infection is usually acquired when living in close proximity to others with active disease, and the family is the main setting for transmission.

Infection spreads through personal contact (via hands, clothes, bedding or hard surfaces) and by flies that have been in contact with discharge from the eyes or nose of an infected person.

Environmental factors associated with more intense transmission of C. trachomatis include:

• Inadequate hygiene.

• Crowded households.

• Inadequate access to water.

• Inadequate access to and use of sanitation.

With repeated episodes of infection over many years, the eyelashes may be drawn in so that they rub on the surface of the eye. This causes pain and may permanently damage the cornea.

Active trachoma is chronic inflammation of the conjunctiva caused by infection with Chlamydia trachomatis. The World Health Organization (WHO) simplified trachoma grading scheme defines active trachoma as:

• Trachomatous inflammation-follicular: the presence of five or more follicles in the central part of the upper tarsal conjunctiva, each at least 0.5 mm in diameter, and/or

• Trachomatous inflammation-intense: pronounced inflammatory thickening of the upper tarsal conjunctiva that obscures more than half of the normal deep vessels.

Cicatricial trachoma is caused by repeated infection with C. trachomatis. It includes the presence of visible scars on the tarsal conjunctiva (trachomatous scarring), shortening and inversion of the upper eye lid (entropion), and malposition of the lashes so that they abrade the eye (trachomatous trichiasis).

Trachomatous scarring can be present without entropion/trichiasis, but if entropion/trichiasis is present because of trachoma, there will be scarring.

Trachoma blindness results from corneal opacification, which occurs because of the mechanical trauma caused by entropion/trichiasis.

Diagnosis

Laboratory tests are not used in endemic areas where the diagnosis is by clinical examination.¹

• Cell culture used to be the standard test but has been superseded by newer tests.

• In other areas, polymerase chain reaction (PCR) and ligase chain reaction (LCR) have high sensitivity and specificity.

• Another new test is direct fluorescein-labelled monoclonal antibody (DFA) and enzyme immunoassay (EIA) of conjunctival smears.

• Giemsa cytology (the finding of intracytoplasmic inclusions) is technically demanding, has a high specificity but low sensitivity.

Trachoma treatment and prevention

A Cochrane review concluded that several studies found modest improvement in vision following intervention. Certain interventions have been shown to be more effective at eliminating trichiasis:³

• Full-thickness incision of the tarsal plate and rotation of the lash-bearing lid margin was found to be the best technique and is preferably delivered in the community.

• Surgery performed with silk or absorbable sutures gave comparable results.

• Post-operative azithromycin was found to improve outcomes where overall recurrence was low.

Elimination programmes in endemic countries are being implemented using the WHO-recommended SAFE strategy. This consists of:¹

• Surgery to treat the blinding stage (trachomatous trichiasis).

• Antibiotics to clear infection, particularly mass drug administration of the antibiotic azithromycin, which is donated by the manufacturer to elimination programmes, through the International Trachoma Initiative.

• Facial cleanliness.

• Environmental improvement, particularly improving access to water and sanitation.

This SAFE approach has been shown to be successful in a number of countries.⁴ Researchers have highlighted the need to focus management on children in order to tackle the problem in its early stages.⁵

Prognosis

Appropriate treatment of early disease gives an excellent prognosis. Severe disease may be stabilised but vision may not improve. Each re-infection worsens the prognosis.