Tuberculosis outbreak in a pre-primary and primary school in Barcelona, Spain.

Background: In June 2022, a case of non-bacillary pulmonary tuberculosis (TB) was reported in a 10-year-old girl attending a primary school in Barcelona. A second pediatric case from the same school was identified in October 2022, prompting the declaration of a TB outbreak and the initiation of an epidemiological investigation. Methods: Contact tracing was conducted using the concentric circles approach, targeting household contacts, classmates, and school staff. Tuberculin skin tests were administered and read 72 h later. Whole genome sequencing of Mycobacterium tuberculosis isolates was performed to identify potential source cases and transmission chains. Results: Among 218 individuals screened, 30 TB infections and 4 TB disease cases were diagnosed. The highest prevalence occurred in grades EP4 and EP5 (ages 9-10), with a significantly higher risk compared to other grades. No adult cases linked to the school were identified. Later, a genomic cluster of 15 cases was detected across Catalonia, suggesting a super-spreading event. However, no direct epidemiological link to the school was established. Conclusions: This outbreak highlights the challenges of TB detection in pediatric populations and the importance of genomic surveillance in tracing transmission. Despite extensive investigation, the source remains unidentified, underscoring the complexity of TB dynamics in urban settings.