Welcome to HCM.
I don't understand why this question is posted to a HIV
specialist. Did your father had any other risk factor for HIV? If so give more details.
While his X-ray and blood parameters are normal and on examination there is nothing wrong with his respiratory system, then it could be a side effect of the drug Amilodepin taken for BP. Change of drug may be beneficial.
Throat and larynx
have to be examined thoroughly for any lesion in these area which would not be covered by X-ray chest.
Wish your father a speedy recovery.