Risk of tuberculosis in children from smear-negative source cases

SETTING: British Columbia, Canada. OBJECTIVE: To determine the frequency of smear-negative tuberculosis (TB) transmission events from adults to children in epidemiologically linked pairs and to determine the predictors for identifying the source case. DESIGN: We extracted demographic, clinical and mycobacteriology information of 190 children with TB and their 83 source cases reported from 1990 to 2001 in the province of British Columbia. Smear-negative transmission events from adults to children were determined by identifying the smear results of epidemiologically linked source cases. We compared the sex, age, ethnicity, contact history, site of disease and tuberculin skin test (TST) results of children who had a source case identified with those who had not. RESULTS: Smear-negative source cases transmitted the disease to 10% of children (95%CI 5-17). Aboriginals (OR 4.9, 95 %CI 1.5-13.4), those with primary TB (OR 7.3, 95%CI 3.3-16.0) and those with a positive TST (OR 2.9, 95%CI 1.2-7.0) were independent predictors for source case identification. CONCLUSION: This study suggests lower rates of transmission of disease to children from smear-negative sources compared to other studies involving all ages. Ethnicity of children, site of disease and a positive TST predict source case identification.