Widal Reaction

WIDAL REACTION aims to determine agglutinins (see Agglutination) for typhoid or paratyphoid bacteria in a patient's blood. This reaction was first proposed by F. Widal (1896). In the blood serum of healthy individuals, agglutinating properties for typhoid bacteria can also be detected, but to a weak degree. In typhoid fever, after 4–8 days of the disease, these properties begin to increase sharply, which makes it possible to diagnose the disease. The Widal reaction can be considered conclusive for typhoid fever if 0.01 cubic centimeters of serum from a suspected patient agglutinates typhoid bacteria. The minimum amount of serum giving agglutination is called its titer. Quite often, by the end of the disease, the agglutination titer in the Widal reaction reaches 0.001–0.0002 cubic centimeters of serum (serum dilution of 1:1,000 to 1:5,000). After recovery, the strength of agglutination gradually drops to normal within 6–8 months, but in some individuals a positive Widal reaction at weak serum dilutions (1:25 to 1:100) persists for years. A negative Widal reaction in typhoid fever is rare (according to Widal, 1 in 163). It can be explained by the absence of protective properties of the serum in exceptionally severe cases or by infection with an atypical variant of typhoid bacteria. In typhoid fever, sometimes simultaneously with the agglutination of the typhoid culture, agglutination of bacteria related to the latter is observed, which can complicate the interpretation of the reaction. Group agglutination in the Widal reaction is especially clearly expressed for paratyphoid bacteria type A and for Gartner's enteritis bacteria (Gartner), while the group agglutination titer is often equal to the main one, and sometimes exceeds it. In such cases, the identification of the main specific reaction can be made by saturating the tested serum with antigen according to Castellani's method (see Agglutinating sera). The interpretation of the results of the Widal reaction can also be complicated by the fact that agglutination in the patient's blood serum may appear as a result of preventive typhoid vaccinations or be activated by other infections. A non-specific Widal reaction is observed in jaundice and bile duct obstruction. Some of these reactions can be attributed to paratyphoid infections accompanied by jaundice (Sacquépée and Fras). The presence of group and non-specific reactions, sometimes remaining for a long time after the disease, especially in bacillus carriers, makes a correct interpretation of the Widal reaction possible only if its results are compared with the clinical picture. The Widal reaction is used, besides typhoid fever, to diagnose paratyphoid diseases, dysentery, glanders, meningitis, and some other diseases. For the diagnosis of typhus, a reaction of the Widal type was proposed by Weil and Felix, and for Malta fever, by Wright. The modern technique of the macroscopic Widal test is precisely described by Hammerschmidt (Hammerschmidt, 1926) and other authors; the standard technique of the microscopic test, adopted in America, is outlined by Wadsworth (Wadsworth, 1927). The macroscopic test deserves preference due to the greater simplicity of execution and accuracy of results. In view of the fact that in the USSR, besides paratyphoid diseases caused by bacteria of types A and B, typhoid-like diseases occur on the basis of infection with Gartner's enteritis bacteria and paratyphoid N, it is desirable for the Widal reaction, in addition to typhoid bacteria, to take cultures of all four mentioned species of bacteria.

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