Participants were recruited over a period of two years from adults over the age of 15 years attending 16 community TB clinics serving a population of ,400,000 in the shantytown of Ventanilla on the outskirts of Lima, Peru ( Figure 1 ). All patients underwent the local standardized clinical workup for TB. This included up to 4 consecutive sputum samples for microscopy and culture. Participation in the study did not change patients' routine clinical management. The local incidence of TB in this population is ,130 per 100,000/year [16] and 95-97% of TB cases are HIV negative [17] . We recruited patients with active TB and individuals, termed symptomatic controls, presenting with respiratory symptoms suspicious of TB in whom TB was subsequently excluded.