This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'Diagnosis of tularemia is confirmed using agglutination testing. In the standard tube agglutination test, what should be the single antibody titre for making the test positive? \nSelect and explain. \nA. 1:40, B. 0.097222222, C. 0.125, D. 0.152777778', 'role': 'user'}, {'content': "Answer: D \nExplanation: A single antibody titer 1:160 is interpreted as a presumptive positive result for diagnosing tularemia. Agglutination test is used to confirm the diagnosis of tularemia. A fourfold increase in titer between paired serum samples collected 2-3 weeks apa is considered diagnostic. Late in infection, titers of 1:20-1:80 may persist for years. Tularemia is caused by F. tularensis, a gram-negative, pleomorphic, nonmotile, non-spore-forming bacillus. Ref: Jacobs R.F., Schutze G.E. (2012). Chapter 158. Tularemia. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds),Harrison's Principles of Internal Medicine, 18e.", 'role': 'assistant'}]