Symptoms
People are typically tested for Salmonella typhi only if they demonstrate the signs and symptoms of a Salmonella typhi infection. The initial symptoms are a high fever, which is typically in the 103 to 104 degrees F range (or 39 to 40 degrees C). Patients with a Salmonella typhi infection may also have a loss of appetite, a headache, or may feel weak. Some patients also get a characteristic rash made up of many flat and pinkish or rose-colored spots. Patients who display these symptoms and may have consumed contaminated food or water are tested for Salmonella typhi.
Culture
A diagnosis of Salmonella typhi can only be confirmed by testing for the presence of the bacteria. Testing most likely involves a blood culture, though the bacteria can also be isolated from the urine, stool, or bone marrow. A sample of the material to be tested (typically blood or stool) is grown in an appropriate medium (either agar or a liquid culture). Bacteria from the culture are then examined under a microscope to look for the presence of Salmonella typhi bacteria. However, according to the Centers for Disease Control and Prevention, a blood culture is only positive in approximately half of all patients with typhoid fever, and a stool culture is often negative during the "acute" (early) phase of the disease. As a result, treatment may be started without a positive culture.
Widal Test
Another method of testing for a Salmonella typhi infection is known as the Widal test. This looks for specific proteins (called agglutinins) that have been made in response to exposure to the Salmonella typhi bacteria. These agglutinins are antibodies that appear in the blood when a person has been infected with the bacteria. As a result, when a blood sample from an infected person is taken and mixed with special characteristic proteins from the bacteria, the blood becomes cloudy as these antibodies bind to the bacterial proteins. Although this test can be unreliable, the test kits are relatively inexpensive and are commonly used in parts of the world where typhoid fever is common.
