Number of negative acid-fast smears needed to adequately assess infectivity of patients with pulmonary tuberculosis.

Study Objectives: To investigate the relationship between the number of negative acid-fast bacilli (AFB) smear results and infectivity of pulmonary tuberculosis (TB).

Design: Retrospective analysis.

Methods And Subjects: We examined 122 index cases in Harris County, TX, reported in 1998 and 1999.