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## London School of Hygiene & Tropical Medicine

Skip to 0 minutes and 12 secondsBy the end of this presentation you should be able to: Define the terms 'epidemiology' and 'prevalence' Explain the methodology used to map trachoma by the Global Trachoma Mapping Project Epidemiology is the study of the distribution and determinants of disease in a population, and the application of this study for public health action. A commonly used epidemiological term is prevalence. Prevalence is a measure of how many people have a disease, in a given population at a specific time. A good analogy for this is looking at a photograph of a group of people and knowing how many people in the photograph have a disease. To calculate the prevalence of disease, we need to know two numbers.

Skip to 0 minutes and 57 secondsFirst, we need to know the total number of people in the population we are studying. For example, a district. Then, we need to know the number of people in that population who have the disease at that specific time. We can obtain these numbers by carrying out a survey. To calculate prevalence we divide the number who have the disease, the numerator, by the population, the denominator. We can then multiply by 100 to get a percentage. In large populations (like districts), it is usually impractical to examine everyone. We therefore generally use sampling to estimate the true prevalence of a disease. Sampling is the recruitment and examination of fractions of the population.

Skip to 1 minute and 40 secondsWe choose our samples carefully so that they have the greatest likelihood of representing the whole population. In trachoma, we define a district as the administrative unit for health care management. Optimally, a district is a population unit of between 100,000-250,000 people. Trachoma is regarded as a public health problem

Skip to 2 minutes and 1 secondif either of the following conditions is true: the prevalence of active (inflammatory) trachoma, TF, is greater than or equal to 5% in children aged 1-9 the prevalence of trachomatous trichiasis, TT, is greater than 0.1% in people of all ages. That is, there is more than 1 in every 1000 people with TT In 2010, trachoma was thought to be endemic - a public health problem - in 2,400 districts worldwide. However, based on district-level surveys, we actually had data on the prevalence of active trachoma in less than half of these districts (1,115 districts). The rest - 1,285 districts - were merely suspected to be endemic. Active trachoma is treated with the antibiotic Azithromycin.

Skip to 2 minutes and 57 secondsAccurate estimates of the prevalence of active trachoma were needed to justify requests for donated azithromycin and, ethically, to implement mass distribution of this antibiotic. Additionally, estimates of the prevalence of trachomatous trichiasis were also needed, to plan for and provide surgery. New, appropriate methodologies had to be developed to implement the Global Trachoma Mapping Project (the GTMP).

Skip to 3 minutes and 25 secondsThese systems and processes had to be: Epidemiologically accurate Simple to use Efficient in human resources terms Following an intensive planning phase, the GTMP systems and processes were field tested in Oromia Region, Ethiopia in October 2012 before the project commenced. Compared to previous trachoma mapping efforts, the GTMP had a number of specific features

Skip to 3 minutes and 50 secondsto help it succeed: A guarantee of data ownership by ministries of health; Standardisation of survey team training and certification, Standardised field methodologies including budgeting, data cleaning, data analysis and data approval; Use of a phone-based app, with state-of-the-art security features, to capture data; Automated linking of prevalence data to the Global Atlas of Trachoma; and finally Centralised funding from a consortium of donors Actual mapping commenced in Oromia, Ethiopia on 17 December 2012 Within 2 months, 100,000 people had been examined across three projects in two countries. With building momentum, it took only 2 more weeks for a further 100,000 people to be examined, now in 6 projects in the two countries.

Skip to 4 minutes and 48 secondsBy the end of the first year, the GTMP had examined 1,096,921 people from 247,220 households in 738 districts. The total population of the 738 districts was estimated to be 101 million people. This figure was calculated from the most recent national censuses. The GTMP finished in January 2016 having mapped 1,546 suspected trachoma endemic districts across 29 countries in Africa, the Middle East, Asia, the Pacific, and the Americas. A total of 2.6 million people had been examined. This required the processing of over 60 million data items. The data collected was representative of a population of 224 million people. The scale reflected a higher than anticipated demand for baseline mapping.

Skip to 5 minutes and 46 secondsThis additional demand was met through a new collaboration with the United States government agency, USAID. USAID supplemented the original funding from the United Kingdom's Department for International Development. Suspected trachoma-endemic districts which remained unmapped by the end of the GTMP were principally those that were insecure or had been identified very late in the project period. Although the GMTP has now ended, the systems and processes developed for it will remain in use. The WHO-led initiative Tropical Data is supporting national programmes to collect and apply epidemiological data about trachoma. Baseline surveys, impact surveys and surveillance surveys can all be supported by the Tropical Data platform. Data generated by the GTMP is now being used by trachoma

Skip to 6 minutes and 38 secondselimination programmes to support key decisions: Where the baseline prevalence of active trachoma (TF) has been found to be 30% or greater, mass antibiotic treatment should be undertaken annually for 5 years. And interventions to improve facial cleanliness and environmental improvement (the F and E components of the SAFE strategy) should also be implemented before re-survey. Where the prevalence of active trachoma is greater than or equal to 10% but less than 30%, mass antibiotic treatment should be undertaken annually for 3 years. And F and E components should be implemented, before re-survey.

Skip to 7 minutes and 15 secondsWhere the prevalence of active trachoma is greater than or equal to 5% but less than 10%, a single round of mass antibiotic treatment should be undertaken, together with F and E interventions, before re-survey. If the baseline prevalence of trachomatous trichiasis (TT) has been found to be greater than 1 in a thousand, patients with TT should be detected and managed in an active manner. If the TT prevalence is found to be less, services for trichiasis surgery should be part of routine eye care.

Skip to 7 minutes and 51 secondsIn summary: Epidemiology describes the magnitude, distributions and determinants of diseases affecting a population Prevalence is a measure of the burden of disease in a population as it is the proportion of the population with the disease at a specified time

Skip to 8 minutes and 10 secondsThe Global Trachoma Mapping Project: Built on earlier work to provide a clear estimate of the need for trachoma elimination interventions worldwide. It was successful due to multiple partnerships at local, regional and global level. And it is an important tool in advocacy work to gain support and funding from partners and governments for trachoma elimination. Finally, the GTMP enables the development of targeted elimination strategies and provides a baseline for monitoring progress towards trachoma elimination worldwide.

# Global mapping of trachoma

In July 2012, Sightsavers, the International Trachoma Initiative (ITI) and the London School of Hygiene & Tropical Medicine, acting on behalf of the International Coalition for Trachoma Control, secured the £10.6M Global Trachoma Mapping Project (GTMP) grant from the United Kingdom’s Department for International Development.

The GTMP was completed in January 2016. It was the largest infectious disease survey ever undertaken, helping to accurately pinpoint the world’s trachoma endemic areas. The sample of 2.6 million people examined during the project represent a global population of 224 million in endemic areas.

A range of partnerships and procedures were needed to carry out the mapping for the GMTP:

• Epidemiologists and ministries of health to construct bespoke sampling frameworks
• Field teams included a grader, recorder, driver and local guide