Trachoma prevalence surveys that include the collection of physical samples for serological and/or infection testing are known by the shorthand ‘plus’ surveys. ‘Plus’ surveys include the collection of dried blood spots (DBS) from finger prick blood to test for antibodies to the Chlamydia trachomatis (Ct) antigen Pgp3 and/or the collection of conjunctival swabs to test for Ct infection.

Over the last 2 years, Tropical Data has been updating its systems and processes to introduce a broader package of support for countries wishing to collect serology and/or infection data as part of routine trachoma prevalence surveys. This is because the clinical sign trachomatous inflammation—follicular (TF) is poorly correlated with evidence of conjunctival Ct infection, especially following antibiotic mass drug administration (MDA). This may result in antibiotic MDA being given unnecessarily, for reasons including there being a lag between clearance of infection and resolution of follicles, or the follicles having a non-trachomatous cause. Adding complementary indicators provides one way of triangulating the TF data with serology/infection data and better tailoring interventions. This can be helpful for districts experiencing unusual epidemiology, such as persistent or recrudescent TF.

The World Health Organization (WHO) Informal Consultation on End-Game Challenges for Trachoma Elimination in December 2021 (WHO 2022) recommended that available evidence on the epidemiology of conjunctival Ct infection, and exposure to Ct infection, be used to help inform tailored management in Evaluation Units (EUs) with persistent or recrudescent TF. In addition, the WHO Diagnostic Target Product Profiles for Trachoma Surveillance includes two other use cases for serology and infection testing at EU level: for baseline mapping in newly suspected trachoma-endemic EUs and for post-validation surveillance (WHO 2024).

WHO is planning to convene a Guideline Development Group (GDG) in 2025 to make formal recommendations on the use of serology in trachoma elimination programmes. In the meantime, a preprint article synthesising the available evidence on serology data for trachoma has made initial recommendations on thresholds in relation to the Pgp3 indicator to inform the GDG process (Kamau et al. 2024). Tropical Data aims to support countries to conform to WHO recommendations. Therefore, the current update is aimed at ensuring the support Tropical Data offers countries remains up to date.

The work Tropical Data has been undertaking aims to support national trachoma programmes to conduct ‘plus’ surveys through an end-to-end process, starting with an established survey methodology, through planning, training, field support, data collection, data cleaning, data analysis, and provision of results. Below is a summary of the extra support Tropical Data has started to put in place (Table1).

 

 Table 1. Adaptations to Tropical Data service to support ‘plus’ surveys

 

Having now introduced a number of the changes, Tropical Data is currently in a piloting phase, during which we are trialling and further refining our package of support. If you are interested in requesting Tropical Data’s support for a trachoma ‘plus’ survey during this pilot phase, please contact Michelle Taylor emichelletaylor@sightsavers.org and/or admin@tropicaldata.org for more information.

 

 

Kamau E, Ante-Testard PA, Gwyn S, Blumberg S, Abdalla Z, Aiemjoy K, et al. Characterizing trachoma elimination using serology. medRxiv [Preprint]. 2024 Sep 24:2024.09.20.24313635. 

 

WHO. Informal consultation on end-game challenges for trachoma elimination, Task Force for Global Health, Decatur, United States of America, 7–9 December 2021. https://apps.who.int/iris/handle/10665/363591. World Health Organization. 2022. 

 

WHO. Diagnostic Target Product Profiles for Trachoma Surveillance. https://www.who.int/publications/i/item/9789240103641. World Health Organization. 2024.