Could a prototype trachoma infection test work in the field?

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In low-prevalence settings and places that have received mass treatment, clinical signs of active trachoma are often present without ocular Chlamydia trachomatis infection. Treatment decisions currently depend on the prevalence of clinical signs, which may lead to unnecessary mass antibiotic distribution. Researchers aimed to evaluate the diagnostic accuracy of a prototype point-of-care (POC) test developed for field diagnosis of ocular C. trachomatis in low-prevalence settings in The Gambia and Senegal.

They conducted three studies, two in The Gambia and one in Senegal. Children under 10 years old were screened for clinical signs of trachoma. Two ocular swabs were taken from each child's right eye. The first swab was tested with the POC test in the field, and two readers independently graded the result. The second swab was tested for C. trachomatis using Amplicor Polymerase Chain Reaction. Field temperature and humidity were measured in Senegal.

In total, 3,734 children were screened: 950 in the first Gambian study, 1,171 in the second and 1,613 in Senegal. Across the studies, sensitivity ranged from 33.3% to 67.9%, specificity from 92.4% to 99.0%, positive predictive value from 4.3% to 21.0%, and negative predictive value from 98.0% to 99.8%. False-positive rates increased markedly at temperatures above 31.4°C and relative humidity below 11.4%.

The researchers concluded that the prototype in its present form is unsuitable for field diagnosis of ocular C. trachomatis because its specificity decreases in hot, dry conditions, where trachoma is predominantly found. Without a suitable infection test, trachoma diagnosis remains dependent on clinical signs. Under current WHO recommendations, the researchers said this is likely leading to continued mass treatment of communities without infection.