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Diagnosis of typhoid fever
Last reviewed: 23.04.2024
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Typhoid fever is diagnosed on the basis of a prolonged fever, headache, increasing intoxication with the development of typhoid status, typical language changes, the appearance of flatulence, rose-rash rash, hepatosplenomegaly and changes in peripheral blood.
Laboratory diagnosis of typhoid fever is based on the detection of an agent in the biomaterial and specific antibodies in the patient's blood. Determining the causative agent in the blood (haemoculture), urine (urinoculture), feces (coproculture), bile (bilikultura), as well as in the bone marrow, cerebrospinal fluid, roseola, pus or exudate is crucial.
In practical work for the early diagnosis of typhoid fever, the most important is the blood culture, which should be carried out throughout the febrile period. Blood from the vein in an amount of 5-10 ml is inoculated into a vial with 50-100 ml of 10-20% bile broth (the best results are seeded in trypsin-soy broth). Positive results of hemoculture are more often obtained with blood cultures during the first week of the disease, when bacteremia is most pronounced. From the second week of illness, typhoid bacilli can be found in feces, urine and duodenal contents. The highest percentage of allocation of sticks of typhoid is obtained from bone marrow cultures. In general, bacteriological confirmation of the diagnosis of typhoid can be obtained in 80-90% of patients.
Serological methods can detect specific antibodies in the blood or antigens in the biosubstrate. In the practical work, Vidal and RNGA reactions (indirect hemagglutination reaction) are most often used with the use of erythrocyte O-, H- and Vi-antigens. Vidal's reaction is based on the detection of specific O- and H-antibodies-agglutinins in the patient's blood with the help of appropriate antigens. Positive results can be obtained from 8-9 days of the disease. Vidal's reaction can be positive in vaccinated and transferred typhoid fever, so the decisive role is the growth of antibody titer in the dynamics of the disease. To more accurately identify specific immune shifts in the patient's blood, Vidal's reaction should be repeated with O- (IX and XII) and H-monodiagnosticums to avoid cross-reactions with salmonella from other groups.
RNGA with erythrocyte O and Vi antigens and the Vi-hemagglutination reaction are more specific and sensitive. These reactions are used for the early diagnosis of typhoid fever. In RNGA, the concentration of O-antibodies increases in the course of the disease, and the titers of Vi-antibodies do not change significantly. The reaction of Vi-hemagglutination is of the greatest importance in the examination of persons suspected of typhoid fever.
Serological reactions to the detection of specific antibodies in the patient's blood should be made from the 4th-5th day of the illness, and then to the 2-3nd week and later. The diagnosis of typhoid fever is considered serologically confirmed at an antibody titer of 1: 200 and above, or with an increase in antibody titer of 2-3 times in the dynamics of the disease. When evaluating serological reactions, it is important to take into account that the growth of titres of specific O-antibodies indicates an acute infectious process, and the presence of only H- or Vi-antibodies - about previously transmitted typhoid or bacteriocarrier.
For serological diagnosis of bacteriocarrier and vaccinal reactions, it has been suggested to separate the specific antibodies related to IgM and IgG in ELISA. The detection of specific typhoid IgM points to the current infectious process, and the isolated detection of specific antibodies belonging to the IgG class is about the vaccinal nature of the antibodies or the previously transmitted typhoid fever.
Differential diagnosis of typhoid fever
In practice, typhoid fever in children is often differentiated with typhoid-like form of salmonellosis, paratyphoid, infectious mononucleosis, lymphogranulomatosis, iersiniosis, malaria, and in the initial period - with influenza, enterovirus infection and acute intestinal infection of other etiology.
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