patient was treated for pulmonary tuberculosis 15...

why did the test appear positive ?
TB patient will always show positive even after treatment , and in that phase its called dormint TB 
what would IGRA test tells you in this case :
its only shows that the patient have been infected by TB , whether its recently or before 
- usually IGRA test show TB but dont differentiate if its active or inactive 
- IGRA is most useful to rule-out active TB 
Is medical intervention need in this case ?
no its not