This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection, Subject name: Medicine
[{'content': 'The single most common cause of pyrexia of unknown origin is - \nSelect and explain. \nA. Mycobacterium tuberculosis, B. Salmonella typhi, C. Brucella spp, D. Salmonella paratyphi A', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Pyrexia of unknown origin is definedvas a temperature persistently above 38 degree celsius for more than 3 weeks,without diagnosis despite initial investigations during 3 days of inpatient care or after more than two outpatient visits. Specific organisms associated with PUP are tuberculosis( extrapulmonary - most common cause), HIV-1 infection,other viral infections (cytomegalovirus,EBV), fungal infections (Aspergillus spp.,candida spp., dimorphic fungi), infections with fastidious organisms(Baonella spp., Tropheryma whipplei). Reference Harrison20th edition pg 1232', 'role': 'assistant'}]