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PRET Antibiotic Study

The PRET antibiotic study is a randomized, community-based trial taking place simultaneously in three African countries of differing trachoma endemicity levels: Tanzania (mesoendemic), Niger (hyperendemic) and The Gambia (hypoendemic).  Study sites were selected based on established local partnerships, the level of commitment to eliminate the disease and generalizability of study results to other countries.

The PRET study will evaluate alternative antibiotic coverage levels and frequencies of mass azithromycin distribution for the treatment of trachoma.  Study data will help to develop a strong evidence base for the long term, mass treatment approach to azithromycin and clear guidelines for when stopping mass treatment is most effective for trachoma control.

Sheila West, PhD, of Johns Hopkins University is principle investigator of this study that will be conducted in Kongwa, Tanzania.

The specific study objectives are as follows:

1. To determine the effective coverage (above 80% in children) of annual mass azithromycin treatment necessary for rapid reduction of infection to less than 5%.

2. To determine the potential re-emergence of infection and disease when using a laboratory-based strategy to identify communities where antibiotic intervention may not be further indicated, based on estimated absence of infection, and communities can be “graduated” from mass treatment.

3.  To determine if mass azithromycin administration every six months is more cost-effective than yearly treatment in rapid reduction of infection in hyper-endemic environments. 

4. Evaluate the effect on re-emergence of graduating villages which have evidence of low rates of infection, or meet World Health Organization (WHO) definition of low disease prevalence.

5. To develop mathematical models for use as public health planning tools to estimate the frequency and coverage of treatment necessary to determine a steep trajectory for elimination.

PRET Countries

The Gambia

In The Gambia, there has been a decline in the national prevalence of active trachoma in recent years--from 20% to 7% in national surveys in 1986 and 1996--but a survey in 2006 showed that substantial parts of Lower River Division (LRD) and North Bank Division (NBD) still have more than 10% prevalence of active trachoma in children under 10 (hypoendemic). In addition, there is evidence that active trachoma persists at potentially blinding levels elsewhere in the country. Our program has identified 11 rural districts (from 5-20,000 population) and a total population of 150,000 who need mass treatment based on the WHO criteria.  The London School of Hygiene and Tropical Medicine is working with this study site.


Trachoma is prevalent throughout Tanzania (mesoendemic), with the Dodoma region exhibiting the highest rates. Kongwa is a district in Dodoma, comprised of 66 villages that have average populations of 2,000-3,000 composed largely of subsistence farmers. In collaboration with Johns Hopkins University, the Kongwa Trachoma Project was started in 1986 to document the burden of disease, and it has since been the field site for studies of trachoma, including the development of diagnostics, immunological studies, and clinical trials of face washing, fly control, and azithromycin use in communities. In this setting, program activities over the last eight years have reduced infection and disease from greater than 50% to 30%, but at a slow pace. We expect that with more rigorous coverage and surveys to stop mass treatment when warranted, we can improve cost effectiveness of the programs. However, provision of quality surgical services is still a massive problem, with recurrence rates reported as high as 45% two years following surgery. 


The Proctor Foundation is working in collaboration with the Niger Ministry of Health and Niger’s country programs. This study site is an area with hyper-endemic trachoma. The study addresses questions of treatment coverage and frequency, and whether treatment of children can reduce infection in the entire community. Matameye was last treated in 2006 and has received no SAFE programming since. The most recent prevalence is 40.5%. In Niger, our program has identified 48 grappes (villages) of population size 250-600 people. No other research partnership has the breadth and ability to undertake such a comprehensive, and critical, proposal for trachoma control. We have proposed the dissemination of results in a format for country National Trachoma Control programs and Ministry of Health, the ultimate end users who need this evidence base to drive improvements in implementation of SAFE for trachoma elimination.