By the end of this presentation, you Explain why antibiotics are used to treat trachoma. Describe the purpose of antibiotic mass drug administration (MDA) for trachoma elimination. And explain the World Health Organization’s guidance on the use of antibiotics for trachoma elimination. The World Health Organization (WHO) recommends two effective antibiotic agents to treat the infection that causes trachoma. Tetracycline eye ointment and oral azithromycin. These antibiotics are used to reduce the level of Chlamydia trachomatis infection in the community. Firstly, by treating infection in individuals with active trachoma. And secondly, mass treatment reduces the transmission of infection from person to person. Fewer infected people equals less reinfection. 1% tetracycline eye ointment is applied twice daily to both eyes for a period of six weeks.
Tetracycline ointment is widely available, but application can be difficult and unpleasant. This means compliance for the full course can be poor. Azithromycin is a broad spectrum antibiotic, which acts by blocking chlamydial replication. Azithromycin is provided in a tablet or suspension form. It is effective as a single oral dose of 20 milligrams per kilogram body weight. To a maximum of one gram in adults. Usually, dosage is determined according to height using a dosing stick. Azithromycin is extremely well tolerated and very safe, even for pregnant women. Usually, the only people who are not given azithromycin are those who are known to be allergic to azithromycin or the drug class to which it belongs, macrolides.
And children aged less than six months who are instead treated with tetracycline eye ointment.
The strategy for antibiotic treatment requires four key questions to be addressed. Number one, who to treat? Infected people only? Pregnant women? Infants? Everyone? Whole communities? Number two, where to treat? Based on the prevalence of active disease or not? Number three, how to treat? Once or twice a year? At the same time as the other community based treatment programmes? And finally number four, when to stop? At what prevalence of active trachoma (TF) should antibiotics be discontinued? When a person acquires a Chlamydia trachomatis infection in the eye, it is not immediately obvious. After a few days a mild inflammation may be visible.
Evidence of active trachoma, graded as TF and/or TI will be seen on examination only after several weeks of chronic or repeated infection. Therefore, if we only treat people with active trachoma, many infected people will remain untreated. And there will be an increased risk of reinfection of treated people from those who are untreated. This pattern was observed in early clinical trials of community based azithromycin. As a result, mass drug administration (MDA) was initiated. And has proven to be much more effective. In MDA events, all members of the target population are offered treatment regardless of whether or not they have active trachoma. As an example, let’s look at District X which has 200,000 people.
About 70,000 of them are aged one to nine years old. The prevalence of TF is 20%. In other words, one in five or 14,000 children age one to nine years have active trachoma in this district. And no doubt, so do some of the older inhabitants. Treating the whole population, and not just those with active trachoma, or just the children, ensures that no one remains infected. And there is no risk of re-infection from within the treated population. Reinfection would only occur through contact with a neighboring untreated area. However, if we only treat half the population in District X, one in ten or 7,000 children will still have untreated active trachoma.
Many of these children will be heavily infected, and will quickly reinfect others in their households, leading to a rapid spread of trachoma infection within District X after the MDA event. In this scenario, the impact of antibiotic treatment in District X would be very limited. The goal of an MDA programme is to treat all the residents in any affected district but this is extremely hard to achieve. Some people will be away on the day of the distribution, some will refuse treatment, and some people will be too sick to take the drug. Because of these challenges, trachoma elimination programs aim to achieve a minimum coverage of 80% for MDA events.
Coverage is defined as the number of people treated with antibiotics, either azithromycin or tetracycline eye ointment, divided by the total number of residents. This is then multiplied by 100 to give a percentage. 80% coverage means that 80 out of every 100 residents in the district are treated. This high coverage reduces how much infection will return before the next round of treatment.
The decision on when to start or stop antibiotic treatment in a district depends on the prevalence of TF in children, aged one to nine years, as measured in a recent baseline survey. If TF is less than 5%, community level antibiotic distribution is not required for trachoma elimination purposes. If TF is less than 10%, but greater than or equal to 5%, plan for one round of MDA, plus interventions for facial cleanliness and environmental improvements, known as F&E. They should be followed by an impact survey six to twelve months after treatment.
If TF is less than 30%, but greater than or equal to 10%, plan for annual MDA for all residents, for three years, plus interventions for F&E, then an impact survey six to twelve months after the final round of treatment. If TF is greater than or equal to 30%, plan for annual MDA for all residents, for five years, plus interventions for F&E and an impact survey six to twelve months after the final round of treatment. The impact survey measures TF prevalence in children aged one to nine years, and the results determine whether or not we need to continue with further rounds of MDA.
Antibiotic treatment in a district is stopped when the prevalence of TF is found to have reached the trachoma elimination threshold, 5% or less. Protocol requires a wait for 24 months after the last impact survey, before a district level pre-validation surveillance survey is conducted. If this survey finds that the prevalence of TF in children aged one to nine years remains below 5%, no more routine interventions or surveys for trachoma elimination are required.
In summary, you should now understand: The decision points for starting and stopping antibiotic treatments for trachoma elimination. Why it is important to achieve high coverage of mass drug administration.