Scientists have developed a cheap, rapid test to determine who has trachoma, the leading infectious cause of blindness in poor countries. The researchers say the new diagnostic tool is much more accurate than the currently recommended observation method and could help limit expensive treatments to only those who need them.
Trachoma, once a scourge everywhere, persists in the developing world. Lack of sanitation and dirty faces invite the organism that inflames the lining of the eyelid and can lead to blindness if untreated.
The World Health Organization says trachoma affects about 84 million people, blinding about eight million. It has set the year 2020 as the target for elimination.
Part of the elimination strategy includes detection, which requires a trained observer to look under the eyelid for telltale redness and white spots. Although this method is simple and cheap, it lacks precision, especially since the white spots can remain long after the infection is gone. So false diagnoses are common, according to Dr. David Mabey of the London School of Hygiene and Tropical Medicine.
"In some communities, you would go on and on giving out antibiotics long after the infection is gone," he said. "That clearly is a waste of resources. The thing about trachoma is that it's a disease of the very poorest people in the poorest countries of the world, so the resources are very scarce."
An expensive laboratory test that detects the genes of the trachoma organism is very accurate, but unaffordable in most places. Now, Mabey and others have developed an accurate but inexpensive chemical test that gives field results in half an hour.
"So the advantage of the new test is it will tell you one way or the other whether infection is present in those communities," he said.
The new technique requires a swab of the inner eyelid and exposes it to a succession of chemicals in two small tubes. If the tested person has trachoma, the liquid in the second tube turns purple in the presence of a dipstick after 25 minutes.
In a trial of more than 600 children in remote Tanzanian villages, the dipstick test was 84 percent accurate in detecting trachoma, compared to 64 percent for the observation method. The false positive diagnoses were less than one percent with the new test, compared to 20 percent for the older method.
"It's measuring what you want to measure," said Dr. Mabey. "Which is, is there infection present in this community?"
The study appears in the journal Lancet. The collaborators say the findings will likely lead to a new approach to trachoma control. But in a Lancet commentary, University of Melbourne doctors Hugh Taylor and Heathcote Wright say more trials are necessary to establish whether the dipstick test will be consistently more reliable than the present observation method.