Sputum induction to aid diagnosis of smear-negative or sputum-scarce tuberculosis in adults in HIV-endemic settings

Sputum induction can aid tuberculosis (TB) diagnosis, but adult data from HIV-endemic environments are limited, and it is unclear how performance varies depending on the clinical context (inpatient versus outpatient), HIV status and whether patients are smear-negative or sputum-scarce. 696 adults with suspected smear-negative or sputum-scarce TB from Cape Town (South Africa) were referred for routine sputum induction. Liquid culture for Mycobacterium tuberculosis served as the reference standard. 82% (573 out of 696) of patients provided a specimen >= 1 mL, 83% (231 out of 278) of which were of adequate quality. 15% (96 out of 652) of sputum induction specimens were culture-positive, and this yield was higher among inpatients versus outpatients (17% (71 out of 408) versus 10% (25 out of 244), p=0.01) and HIV-infected versus uninfected patients (17% (51 out of 294) versus 9% (16 out of 173), p=0.02), but similar for CD4 (>200 versus <= 200 cells.mu L-1) and patient (smear-negative versus sputum-scarce) subcategories. Overall sensitivity (95% CI) of smear-microscopy was 49% (39-59%), higher among inpatients versus outpatients (55% (43-67%) versus 32% (14-50%), p=0.05), but unaffected by HIV co-infection, CD4 count or patient type. 29% (203 out of 696) of patients commenced anti-TB treatment and sputum induction offered microbiological confirmation and susceptibility testing in only 47% (96 out of 203). Under programmatic conditions in an HIV-endemic environment although the yield of culture was approximately two-fold higher amongst HIV-infected patients and inpatients, a fifth of all patients were unable to provide a specimen following sputum induction. Same-day microbiological diagnosis was only possible in 50% of patients.