Immunologic-Based Diagnosis of Latent Tuberculosis among Children Less Than 5 Years of Age Exposed and Unexposed to Tuberculosis in Tanzania: Implications for Tuberculosis Infection Screening

BACKGROUND Childhood tuberculosis (TB) is acquired following exposure to an infectious TB case, often within the household. We prospectively screened children 6-59 months of age, exposed and unexposed to an infectious TB case within the same household, for latent tuberculosis infection (LTBI), in Dar es Salaam, Tanzania. METHODS We collected medical data and clinical specimens (to evaluate for helminths, TB and HIV coinfections) and performed physical examinations at enrollment and at 3-month and 6-months follow-up surveys. LTBI was assessed using QuantiFERON (QFT) at enrollment and at 3 months. RESULTS In total, 301 children had complete data records (186 with TB exposure and 115 without known TB exposure). The median age of children was 26 months (range 6-58); 52% were females, and 4 were HIV-positive. Eight children (3%) developed TB during the 6-month follow-up. We found equal proportions of children with LTBI among those with and without exposure: 20% (38/186) vs. 20% (23/115) QFT-positive, and 2% (4/186) vs. 4% (5/115) indeterminate QFT. QFT conversion rate was 7% (22 children) and reversion 8% (25 children). Of the TB-exposed children, 72% initiated isoniazid preventive therapy (IPT), but 61% of parents/caregivers of children with unknown TB exposure and positive QFT refused IPT. CONCLUSIONS In this high burden TB setting, TB exposure from sources other than the household was equally important as household exposure. Nearly one third of eligible children did not receive IPT. Evaluation for LTBI in children remains an important strategy for controlling TB, but should not be limited to children with documented TB exposure.