Benefit of amoxicillin in differentiating between TB suspects whose initial AFB sputum smears are negative.

SETTING: Out-patient dispensary in Conakry, Guinea, West Africa. OBJECTIVE: To differentiate between pulmonary tuberculosis (PTB) and non-PTB diseases among 204 acid-fast bacilli (AFB) smear-negative adult TB suspects. DESIGN: We derived scores from clinical, serological and radiological findings among PTB suspects aged > or = 15 years who, after having had three AFB-negative smears, were treated for 10 days with amoxicillin (AMX, 1.5 g/day). RESULTS: At the selected cut-off score from model 1 (clinical), sensitivity for PTB was 95%, specificity 40%, negative predictive value (NPV) 84%, and positive predictive value (PPV) 69%. Comparable values from model 2 (clinical + serological + radiological) were: sensitivity 99%, specificity 45%, NPV 97%, and PPV 71%. Results from AMX were better: sensitivity 92%, specificity 93%, NPV 94%, and PPV 91%. Of the 117 suspects who failed to respond clinically and radiographically to AMX and remained AFB smear-negative, 110 (94%) had PTB, confirmed either by positive culture (73 patients) or response to anti-tuberculosis treatment (37 patients). CONCLUSION: The clinical and radiographic response to AMX is better than derived scores at differentiating between PTB and non-PTB in TB suspects presenting to a dispensary in Guinea, a low HIV-seroprevalence country.