Typhoid fever, a bacterial infection caused by Salmonella typhi and paratyphi, may prove dangerous if not diagnosed and treated on time. Untreated typhoid may result in serious complications like intestinal perforation, peritoneal infection, and intestinal bleeding or ulcers. These harmful possibilities make the early diagnosis and typhoid fever treatment very important. A laboratory typhoid test can confirm the diagnosis of typhoid fever.
Take A Typhoid Test
Here are some of the common typhoid tests conducted as part of typhoid diagnosis.
An Introduction To The Widal Test
- The Widal test detects the presence of the antibodies that act against the antigens of typhoid bacteria. The substance that triggers the formation of an antibody is called an antigen and a particle produced by the body on exposure to an antigen is called an antibody.
- During typhoid infections, two types of antigens namely ‘H’ and ‘O’ are present in the blood of the patient. The antigen ‘H’ is derived from the flagella (a tail-like structure) of bacteria, while the antigen ‘O’ comes from the body of these organisms.
- When a person acquires a typhoid infection, these antigens are sensed as foreign particles by the body and in response to them, the body produces antibodies. These antibodies can be detected with the Widal test.
How Is The Widal Test Done?
- In a test tube (or over a glass slide) the blood sample taken from the patient is allowed to react with a solution that contains antigens (H and O) of typhoid bacteria. Now, if the blood contains antibodies against these antigens, clumping appears in the mixture. This clumping can be seen with naked eyes.
- Serial dilutions of Salmonella antigens are done in different test tubes (or on slides) and the patient’s blood, taken as a sample, is mixed with them. The level of specific titre (concentration) is noted and the result is interpreted accordingly. A titre that exceeds 200 for antigen H and a titre above 100 for antigen O antigen are considered as significant.
Facts Related To The Widal Test
- The Widal test is not very accurate. Also, the results of multiple tests are more reliable as a single test might not prove conclusive. Though it is easier, faster, and cheaper to perform than other tests, the Widal test has a few limitations.
- It cannot distinguish between the antibodies present due to the current infection and the ones left over from previous infections.
- There is a chance that other infections may yield a positive result on this test.
- Patients who have been vaccinated against typhoid may also show positive results on the test.
- The Widal test may be negative in the first week and the titres begin to rise at the end of the first week or at the beginning of second week. Between the second and fourth week, the titres rise gradually and then decline slowly.
- Patients treated with antibiotics may not show any rise in titres.
Culture is probably the only specific method to diagnose typhoid. It is considered as the ‘Gold standard’ method for diagnosing typhoid fever. Cultures can be generated using samples like blood, urine, stool, bone marrow, and intestinal secretions. One of these samples is spread over specific culture media that is designed to favor the growth of Salmonella. The culture shows typical characteristics that help identify these bacteria.
Stool culture may remain negative during the first week. It becomes positive by the third week of typhoid, if it has not been treated until then. Stool culture is a good way of detecting a long-term carrier state, as the carrier person can shed Salmonella for more than a year.
Results of a blood culture may vary as per the duration of the illness. High yield may be observed during the first week of infection and this decreases gradually by the third week. The yield of the culture is determined by the number of Salmonella bacteria present. There are chances that with antibiotic therapy, the yield will decrease.
Bone Marrow Culture
It is a more sensitive method than blood culture to detect the presence of the Salmonella bacteria.
Intestinal Secretion Culture
Culture generated from intestinal secretions may show a positive result even when the bone marrow culture gives a negative result. This helps eliminate any false negatives.
Typhidot-M, a new typhoid test, detects IgM and IgG (Immunoglobulins M and G) type of antibodies in the blood of the patient. Typhidot is capable of detecting typhoid within 2-3 days of infection and its results can be generated within few hours.
IgM antibodies are indicative of recent infection while IgG antibodies indicate past infection. As Typhidot can distinguish between IgM and IgG, it becomes easier to diagnose recent infections.
The Widal test, though not very specific for the diagnosis of typhoid, is usually the typhoid test of choice due to its simpler, faster, and cost-effective method. Typhoid can turn fatal if it is not diagnosed and treated in a timely manner. If you suspect a typhoid infection or see any typhoid fever symptoms, consult a doctor immediately.