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
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? 
Select and explain. 
A. 1:40, B. 0.097222222, C. 0.125, D. 0.152777778
D: 0.152777778
Answer: D: 0.152777778 
Explanation: 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.