Active TB cases were recruited on the basis of positive sputum microscopy with subsequent confirmation by culture. Mycobacterial culture was by automated liquid culture (BACTEC MGIT 960 TM , BD) as well as the Microscopic Observation Drug Susceptibility (MODS) assay which we have previously established as a standard local laboratory protocol [18] and which has since been adopted as the standard operating procedure by the national TB programme in Peru. Symptomatic controls, those patients with respiratory symptoms without active TB, were recruited if they had a persistent cough and one or more of the following clinical features: fever, weight loss, decreased appetite or haemoptysis. Symptomatic controls had 1-4 sputum smears and cultures to exclude active TB and were followed for 6 months to confirm that cultures had not become positive or were re-classified accordingly. Additional TB cases and symptomatic controls were identified through tracing household contacts, from whom sputum smears and cultures were obtained if symptomatic.