This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Gram Positive Bacilli, Gram Negative Bacilli), Subject name: Microbiology
[{'content': 'Typhoid in first week of illness is best diagnosed by:- \nSelect and explain. \nA. Serum widal test, B. Stool culture, C. Urine test, D. Blood culture', 'role': 'user'}, {'content': "Answer: D \nExplanation: Laboratory diagnosis of typhoid : 'BASU' mnemonic Test of diagnosis Time of diagnosis Remarks Blood culture 1st week Mainstay of diagnosis Antibodies (widal test) 2nd week Moderate sensitivity & specificity Stool culture 3rd week Useful for carries Urine test 4th week Useful for carries", 'role': 'assistant'}]