Background: Trachoma is a blinding disease caused by conjunctival infection with Chlamydia trachomatis (Ct). Mass drug administration (MDA) for trachoma control is administered based on the population prevalence of the clinical sign of trachomatis inflammation - follicular (TF). However, the prevalence of TF is often much higher than the prevalence of Ct infection. The addition of a clinical sign specific for current ocular Ct infection to TF could save resources by preventing unnecessary additional rounds of MDA.
Methods: Study participants were aged between 1-9 years and resided on 7 islands of the Bijagos Archipelago, Guinea Bissau. Clinical grades for trachoma and corneal pannus and ocular swab samples were taken from 80 children with TF and from 81 matched controls without clinical evidence of trachoma. Ct infection testing was performed using droplet digital PCR.
Results: New pannus was significantly associated with Ct infection after adjustment for TF (P = 0.009, OR = 3.65 (1.4-9.8)). Amongst individuals with TF, individuals with new pannus had significantly more Ct infection than individuals with none or old pannus (75.0% vs 45.5%, Chi(2) P = 0.01). TF and new pannus together provide a highly specific (91.7%), but a poorly sensitive (51.9%) clinical diagnostic test for Ct infection.
Conclusions: As we move towards trachoma elimination it may be desirable to use a combined clinical sign (new pannus in addition to TF) that is highly specific for current ocular Ct infection. This would allow national health systems to obtain a more accurate estimate of Ct population prevalence to inform further need for MDA without the expense of Ct molecular diagnostics, which are currently unaffordable in programmatic contexts.