Thigh Abscess Post-vaccination - Do Not Forget Tuberculosis!

Injection site abscesses are common post-immunization complications, typically caused by pyogenic bacteria.Tubercular abscesses at injection sites are rare, with a few cases linked to Mycobacterium tuberculosis (MTB).We present a 2-year-old boy with progressive necrotic cervical lymphadenopathy for 1 year, left thigh swelling for 5 months, onset of which was 4 weeks after diphtheriapertussis-tetanus vaccination at 16 months of age.He developed fever, purulent discharge from swelling and increase in swelling size 2 weeks prior to presentation.Ultrasound of thigh showed a thick-walled collection, suggestive of an abscess.Incision and drainage was performed, and pus detected rifampicin sensitive MTB-complex.Specific testing for M. Bovis was not done.Neck ultrasound showed necrotic cervical nodes and chest X-ray showed bilateral perihilar opacities.The child was previously vaccinated with Bacillus Calmette-Gurin in the left upper arm and had no known TB contacts.He was treated with incision and drainage of the abscess, followed by first-line anti-tubercular therapy with isoniazid, rifampicin, pyrazinamide, and ethambutol.At two months follow-up, ultrasound showed complete resolution of thigh abscess and non-necrotic cervical lymphadenopathy with reduction in node size.This case highlights the need for awareness of post-vaccination injection-site tubercular abscesses, particularly in children with an existing distant tubercular focus.