A new mathematical model, based on known disease transmission rates, predicts that plans to eliminate the leading cause of preventable blindness cannot succeed unless the worst pockets of infection receive special treatment.
Trachoma, a bacterial eye infection, affects some 150 million people worldwide. Children are particularly vulnerable. Reinfection causes scarring that can lead to blindness, and currently, some six million people have been left sightless from the infection. Arid, rural regions of Africa, the Middle East and parts of Asia are areas of the greatest concentration.
The infection is completely treatable with antibiotics and is the target of a planned World Health Organization (WHO) project, "GET 2020" (Global Elimination of Trachoma by the year 2020).
The plan is to treat infected people with a proven antibiotic called azithromycin, donated by Pfizer Inc. Although WHO has not yet announced its final treatment strategy, plans most often aired involve annual antibiotic treatments for people in the affected regions, along with cleaning water supplies and encouraging improved face washing.
But while annual antibiotic treatment will eliminate the disease in most regions, it will not be sufficient to do so in the areas where trachoma among children is most prevalent, according to computer projections developed by researchers at the University of California San Francisco. They report their findings in the May, 1999 issue of Nature Medicine.
"Our model shows that in areas where the incidence of trachoma is high - where more than half of the kids are infected - the disease will just bounce back after the annual treatment due to reinfection," said Tom Lietman, MD, lead author of the report and assistant professor of ophthalmology at UCSF's Proctor Foundation. Reinfection can lead to blindness.
"These areas of high incidence may make up only about 10 percent of all regions affected by trachoma, but it is in these areas of higher incidence that the rate of blindness is much higher," Lietman explained.
The good news offered by the models, the UCSF researchers say, is that annual antibiotic treatment will eliminate trachoma in most regions, and that by treating the worst pockets of infection twice a year instead of annually, this blinding scourge can, in fact, be purged.
"We're not going to know for years whether any of the suggested treatment strategies will work, so we need mathematical models to project the outcomes of different options," Lietman stressed. The models are similar to those pharmacologists use to determine antibiotic dosages in individuals, he explained.
Lietman and his colleagues are also involved in clinical trials in Nepal, comparing the effectiveness of different strategies for treating whole villages or subsets of them. Prime candidates considered by practitioners are treating everyone in a village where trachoma is present, treating only children 10 and under, and treating only children with active infections and all members of their households.
Senior author on the paper in Nature Medicine is Sally Blower, PhD, associate professor of microbiology, immunology and medicine at UCSF. Also collaborating on the research, and co-authors on the paper, are Travis Porco, PhD, research scientist in the AIDS office at the San Francisco Department of Public Health and previously a post-doctoral fellow at UCSF, and Chandler Dawson, MD, professor of ophthalmology at the Proctor Foundation at UCSF.
The research was funded by the National Institute of Allergy and Infectious Diseases.
Journal
Nature Medicine