Trachoma is the leading infectious cause of blindness worldwide. In April 2023, it was a public health problem in approximately 40 countries, with an estimated 116 million people at risk and 1.5 million people affected by the late blinding stage of the disease. About 84% of those at risk of trachoma blindness are in the World Health Organization (WHO)’s African Region.
Trachoma is caused by ocular infection with the bacterium Chlamydia trachomatis, which results in inflammation of the conjunctiva. This is known as “active trachoma”. C. trachomatis infection is mainly found in children. After many episodes of repeated reinfection, the upper conjunctiva can become scarred, causing the eyelashes to turn inwards, scratching the eyeball. This is known as trachomatous trichiasis (TT); it becomes more common in middle and older age groups. If left unmanaged, TT can lead to irreversible corneal damage and blindness.
Transmission of C. trachomatis from person to person occurs through contact with nasal and/or ocular discharge of infected people, in fomites, and indirectly via eye-seeking flies.
The WHO-endorsed strategy for trachoma elimination is known as SAFE: Surgery for TT, Antibiotics to clear infection, and Facial cleanliness and Environmental improvement to limit transmission. Surgery is offered at an individual level to those with TT, whereas the “A, F and E” components are implemented at the evaluation unit (EU) level (the unit for healthcare management, generally with a population of 100,000–250,000 people). Antibiotics are distributed through mass drug administration (MDA) of whole EUs that have a moderate to high prevalence of active trachoma. Health promotion and improvements to water, sanitation, and hygiene (WASH) access aim to achieve the “F” and “E” components.
Available diagnostic tools
In trachoma prevalence surveys, trachoma is diagnosed using the WHO simplified grading system, which was designed for use by non-specialist personnel. The key signs for programmatic decision-making are TF, a sign of active trachoma that is associated with ocular C. trachomatis infection, and TT. Concerted efforts have been made to standardize and quality-assure the assessment of these signs in population-level surveys. However, a growing body of evidence highlights their limitations, including the poor sensitivity and specificity of TF as a marker for C. trachomatis infection (especially post-MDA), inherent subjectivity, and difficulty of training graders as trachoma prevalence falls and cases become rarer. Non-TF-based diagnostics are likely to have particular utility in the surveillance phase of programmatic work.
The target product profile
The purpose of this TPP is to communicate platform-agnostic recommendations for how a diagnostic for trachoma surveillance at EU level should perform. WHO is seeking feedback on the draft TPP from experts in the diagnostics industry, product developers, the scientific community, NTD programme personnel and clinicians currently involved in trachoma elimination work.
Details may be found in the linked document.
Proposed revisions arising from the public consultation will be considered by the TPP working group before the document is finalized. The final TPP will be used for the development of diagnostics for trachoma elimination programmes.
If you have any comments, please email Dr Anthony Solomon (solomona@who.int), including “TPP trachoma surveillance” in the subject field.