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: Microbiology
[{'content': "Following are true of Widal test except - \nSelect and explain. \nA. High titre in first sample is diagnostic, B. 'H' antigen is specific for serotyping, C. Highly +ve H titre not diagnostic, D. Maximum titre in third week", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e., High titre in first sample is diagnostic . High titre may be persent due to prior infection or immunization. It is the rising titre in two or more sequential samples which is suggestive of typhoid fever (not high titre in first sample). . The genus salmonella is fuher subdivided into serovars based on the detection of three major antigenic determinants. . Somatic antigen 0 . Surface antigen Vi . Flagellar antigen H . The titre increases steadily, reaching maximum in the 3" or 4\'h week.', 'role': 'assistant'}]