Twins with Tuberculous Abscesses in the Left Thigh Vaccination Site - Is it BCG or Mycobacterium Tuberculosis?

Patient 1, a 3-month-old girl, born preterm in March 2024 at 34 weeks and 4 days with a birth weight of 1.9 kg, was the first-born twin.She was admitted to the neonatal intensive care unit (NICU) for 10 days due to neonatal hyperbilirubinemia (NNH).She received the Bacillus Calmette-Gurin (BCG) and Hepatitis B vaccines 3 weeks after birth.She presented in June 2024 with a painful, erythematous lump over the left thigh injection site, first noticed 1 month post-vaccination.There is no history of tuberculosis (TB) contact.On presentation, her weight was 3.71 kg (below 3 rd percentile as per Indian Academy of Pediatrics (IAP) growth charts).On examination, a tender, mildly erythematous swelling was present in the left thigh with mild purulent oozing.No scar was seen over the left deltoid.Other general and systemic examinations were normal.Thigh ultrasound (USG) showed a thick, irregularly walled collection in the intramuscular plane measuring 2.1x1.8x1.4 cm containing 2.8 mL of fluid showing moving internal echoes, suggestive of an abscess.She was given oral amoxicillin-clavulanic acid for 5 days.A repeat USG found 2.3 mL of fluid.USG-guided drainage was done following which the volume reduced to 0.3 mL.She was discharged on oral linezolid for 12 days.Pus sent for Xpert MTB/RIF detected Mycobacterium tuberculosis complex (MTBC) and reported it as rifampicin sensitive.Other investigations are shown in Table 1.She was prescribed a local betadine ointment and was asked to follow-up with a repeat USG.