**Core Concept**
The Wide test, also known as the Widal test, is a serological agglutination test used for the diagnosis and confirmation of typhoid fever. It measures the presence of antibodies against the O and H antigens of Salmonella Typhi in the patient's serum.

**Why the Correct Answer is Right**
The Widal test detects IgM and IgG antibodies against the O and H antigens of Salmonella Typhi, which are produced in response to the infection. The test involves mixing the patient's serum with antigens of the bacteria, and agglutination (clumping) of the red blood cells is observed if antibodies are present. The test is usually performed in two stages, with the first stage measuring IgM antibodies, which appear early in the infection, and the second stage measuring IgG antibodies, which appear later.

**Why Each Wrong Option is Incorrect**
**Option B:** The Elek's test is a precipitation test used for the detection of diphtheria toxin and not related to typhoid diagnosis.
**Option C:** The Mantoux test, also known as the tuberculin skin test, is used for the diagnosis of tuberculosis and not related to typhoid fever.
**Option D:** The Wasserman test is a precipitation test used for the diagnosis of syphilis and not related to typhoid fever.

**Clinical Pearl / High-Yield Fact**
The Widal test is a classic example of an agglutination test, which detects the presence of antibodies against specific antigens. It is essential to remember that the Widal test is not a confirmatory test for typhoid fever, as it can yield false-positive results in patients with other infections or in individuals who have been vaccinated against typhoid.

✓ Correct Answer: A. Wide test