Typhoid fever is an acute infection, the diagnosis of which occurs through a complex of tests. One of the methods to confirm the diagnosis is Vidal's reaction, which is performed no earlier than the second week of infection.
Before this, the diagnosis is established by a blood test, urinalysis and by detecting symptoms of the disease, such as:
- intoxication of the body;
- rash;
- fever;
- increased volumes of liver and spleen;
- bradycardia .
Vidal's agglutination reaction
Typically, typhoid fever is diagnosed by serological testing. In the blood serum, agglutinating properties are found (in a healthy person these indices are not noticeable). But only on the eighth day of the disease can you establish such changes, as a result of which it becomes possible to accurately determine the disease.
For the diagnosis, the agglutination test titer of Vidal type should be in a 1: 200 ratio. At the same time, one can conclude that the disease exists, if at least in the first test tube with a 1: 200 substance ratio agglutination occurred. If there was a group agglutination with simultaneous exposure of several antigens, the causative agent of the infection is the one where the reaction occurred in the greatest dilution.
Statement of the reaction of Vidal
The patient takes three milliliters of blood from the vein (at the elbow area). Then, after waiting for it to coagulate, the serum is separated, which is then used to prepare the dilutions:
- Each tube is filled with saline (1ml).
- After that, another milliliter of serum is added to it (diluted 1:50). As a result, a dilution of 1: 100 is obtained.
- Further from this flask the substance is added to the next one, in which there is already saline solution. As a result, the ratio is 1: 200.
- In the same way, dilutions of 1: 400 and 1: 800 are achieved.
- At the end, each flask is filled with a diagnosticum (two droplets) and sent to the thermostat for two hours at 37 degrees.
- After the vials are removed and left to show the reaction. The final result becomes known the next day.
Disadvantages of the method
Vidal's reaction to typhoid fever is simple and convenient, but it has a number of disadvantages:
- Determine the pathology can only be from the second week of infection.
- With antibiotic therapy or severe ailments, negative results can be observed.
- In persons who have undergone paratyphoid or typhoid fever, on the contrary, there is a positive reaction.
In more accurately diagnose, Vidal's reaction should be repeatedly set in about five to six days. At infected, the antibody titer increases in the period of the disease.