Disseminated Bacille Calmette-Guérin Vaccine-Induced Disease in a Sample of Iranian Children: A Longitudinal Case-Series Study

Background: Approximately a quarter-million Iranian newborns receive the Bacille Calmette-Guérin (BCG) vaccine annually. However, in immunodeficient infants, this vaccine can lead to disseminated BCG disease (DBD). Objectives: This study aims to determine the clinical presentation, comorbidities, underlying immunodeficiency, and prognosis of DBD in a group of Iranian children. Methods: In a longitudinal case-series study, data were collected from the files of infants and children diagnosed with DBD from 2005 to 2017. Immunodeficiency screening was conducted for each patient. For children with normal immunodeficiency screening results, further testing for Mendelian susceptibility to mycobacterial diseases (MSMD) was performed. Detection of DBD in children was achieved by evaluating gastric lavage and bone marrow aspiration samples for mycobacterium. Results: Most of the 22 patients were immunocompromised, with the following distribution: 31.8% had severe combined immunodeficiency (SCID), 45.5% had MSMD (specifically IL-12Rβ1 deficiency), one patient (4.5%) had Wiskott-Aldrich syndrome (WAS), and the remaining 18.1% had unknown immunodeficiency types. Most patients with MSMD were successfully treated and did not show relapse during the follow-up period, even after discontinuing anti-tuberculosis (TB) medications. Conclusions: Due to the similarity of its manifestations to sepsis, diagnosing systemic infections caused by the BCG vaccine in children requires a high level of clinical suspicion and appropriate diagnostic measures, such as mycobacterial culture, biochemical speciation, or polymerase chain reaction (PCR). These diagnostic steps should be taken promptly in cases of DBD, with concurrent treatment using anti-tuberculosis drugs and, if possible, targeted therapies for underlying immunodeficiency.