What is Which among the following is NOT TRUE regarding Widal test? and explain in detail?
Widal test is used for the measurement of H and O agglutinins for typhoid and paratyphoid bacilli in patients sera. Two types of tubes are generally used, a narrow tube with conical bottom (Dreyer's) for H agglutination and a sho round bottom (Felix) for O agglutination. Equal volumes of serial dilution of the serum and the H and O antigens are mixed in the tubes and incubated in a water bath at 37 degree overnight. H agglutination leads to the formation of loose, cotton wool clumps, while O agglutination is seen as disc- like pattern at the bottom of the tube. Results are interpreted taking into the following: The agglutination depends on the stage of the disease. It usually appear by the end of 1st week. Demonstration of rise in titre of antibody by testing 2 or more serum samples is more meaningful than single. 1/100 or more for O agglutination & 1/200 or more for H agglutinins are significant. H agglutinins persist longer than O Persons who have prior infection / immunisation may develop an anamnestic response. Bacterial suspensions used as antigens should be free of fimbria Cases treated with chloramphenicol show poor agglutinin response. Ref: Ananthanarayanan & Paniker's textbook of microbiology Ed 8 Pg - 296.