A 14 yrs old young female presented to us with high grade fever since last 20 days. She had calf pain for 3-4 days during illness. On 4th day of admission she developed generalised erythematous maculopapular rash with itching. No other positive history. No H/O bone pain, any tenderness, altered sensorium. No LNpathy systemic exam- Normal. Her CBC showing polymorphonuclear leucocytosis with total counts upto 22000/mm3. CRP 42. LFT, KFT, Na/K, HIV/HbsAg, RBS- normal Sr uric acid, CPK- Normal Montoux Widal : Negative ANA RA factor Urine R- Normal Bone marrow aspiration - Normal CxR & USG abdomen- Normal Despite giving cefuroxime & amikacin & paracetamol, she is getting continuous high grade fever. In view of drug fever we stopped all drugs for 72 hrs but fever has not come down. What might be the possibitity, next investigation?