PHILADELPHIA—Instead of mass treatment of whole populations in areas affected by trachoma it is more cost-effective in many situations to check first which children are infected and treat only these. This is according to research from The Gambia conducted by the London School of Hygiene & Tropical Medicine and discussed in Philadelphia at the annual meeting of the American Society of Tropical Medicine and Hygiene. But whether to go for mass treatment or diagnosis depends on costs: and these are changed if the antibiotic treatment for this blindness-inducing disease is donated. Professor Robin Bailey explained to Peter Goodwin how the availability of inexpensive rapid diagnostic tests means that many unaffected children could now be spared treatment.