Following are true of Widal test except -

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.