Study suggests new approach may be needed for treating infectious blindness

Programmes may need to treat everyone who is living with someone infected with trachoma, say researchers <em> - News </em>

By Laura Gallagher
Tuesday 31 March 2009

Health programmes dealing with the infectious eye disease trachoma may need to treat everyone who is living with an infected person in order to bring the disease under control, suggests new research.

Trachoma is the world's leading cause of infectious blindness. Although it has almost been eradicated in the developed world, the disease is still endemic in some developing countries. Globally, eight million people are visually impaired from the disease and a further 46 million people with early stage disease are in need of treatment to prevent blindness.

The new research, published in PLoS Neglected Tropical Diseases on 30 March 2009, reveals that people are much more likely to become infected with trachoma as a result of living with an infected person than as a result of picking up the infection in the community. The researchers suggest that control programmes may need to treat everyone who lives in an infected household in order to eliminate trachoma from that household and bring the disease under control. However, they stress that further research is needed to explore the effectiveness of this strategy.

Trachoma can spread when bacteria are transferred from a person's hands or an everyday object, or when flies pick up bacteria from one person and transfer them to another. People who live in households where there has been trachoma infection in the past can become re-infected unless the bacteria are completely eliminated. Those who suffer from repeated trachoma infections are increasingly likely to develop serious eye problems.

In 1998, a global initiative was launched under the World Health Organization's leadership for the Global Elimination of Trachoma by 2020. Its strategies for combating the disease include targeting any community where 10 percent or more of the children show signs of early trachoma and treating everyone in that community with antibiotics. Unfortunately, it can be difficult to treat all members of a community, because people are often away from the community at the time of treatment, for example if they are busy farming. The potential impact of more focused treatment, targeting infected households, had not been estimated prior to the new study.

Control programmes may need to treat everyone who lives in an infected household in order to eliminate trachoma from that household, according to the new study

The researchers used mathematical modelling to explore how trachoma was being transmitted in four communities in the Gambia and Tanzania. On average, 71 percent of infections occurred as a result of the bacteria being transmitted within a household. The study also showed that people living in large households contributed more to the incidence of infection than those in smaller households. The researchers suggest that this is because individuals contact people that they live with more than the rest of the community. In areas with high household transmission, the more people an individual lives with, the higher the chance of them becoming infected from a household member.

Isobel Blake, the lead author of the study from the Division of Epidemiology, Public Health and Primary Care at Imperial College London, said: "Trachoma can be a very debilitating disease - it is difficult for people in the developing world to work and get on with their everyday lives if they lose their sight.

"Our research shows that the bacterial infection which causes trachoma can spread really easily within a household. This happens through contact with an infected person's hands, or with objects like towels and clothing that have picked up the bacteria, or with flies, which transfer the bacteria from person to person. If control programmes make sure they treat everyone who is living with an infected person, they can greatly reduce the spread of the infection."

David Mabey, another author of the paper from the London School of Hygiene and Tropical Medicine, said: "We have known for many years that cases of trachoma tend to cluster within households. This paper is the first to compare rates of transmission within and between households. We have shown that within-household transmission is far more efficient, and accounts for almost three quarters of new infections across the four communities we studied.

"Failure to treat all infected members of a household during the mass administration of antibiotics is likely to lead to the rapid re-infection of that household, followed by a more gradual spread across the community. It is important to achieve high treatment coverage of infected households in mass treatment campaigns," he added.

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