Q. What are the different methods for performing Widal test?
Widal test can be performed by the following two different methods:
1. Slide agglutination Widal test
Qualitative Slide Test
Quantitative Slide Test
2. Tube agglutination Widal test
Tube agglutination is the recommended method as it has more accuracy. However, Slide agglutination is preferred by some as it gives the rapid result. Tube agglutination method requires approximately 18 hours for test completion.
Q. Is there any risk associated with this test?
There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising or infection at the site of needle prick.
Q. What are the limitations of Widal test?
The limitations of Widal test are:
Previous typhoid vaccination may result in increased antibody titres in the non-infected persons
False positive Widal test can occur in patients with non-enteric Salmonella infection, for example Typhus, Immunological disorders, chronic liver disease, Malaria and cryptococcal meningitis
Prior use of antibiotics can affect antibody response giving a low titre in the Widal test even in the presence of bacteriologically confirmed typhoid fever
The Widal agglutination titre varies with the geographic location based on the prevalence of Salmonella infection in that area
Past infection with serotype Typhi or another nontyphoidal Salmonella serotype also results in false positive Widal test
Q. What are the other tests to diagnose Enteric fever?
The other tests which are used to diagnose Enteric fever include Blood culture test, Widal test, Stool culture test, and Urine culture test. Among these, blood culture is the most commonly recommended method for diagnosing Enteric fever and is performed during the first week of fever. If in case other test results come inconclusive then bone marrow samples can be used to diagnose any infections.
Q. How can you prevent typhoid fever?
Avoiding contaminated foods and drinks can help to prevent typhoid fever. Along with that, proper vaccination against typhoid fever can also keep a check on developing any possible case of infection.
Q. What is the appropriate time during illness for performing Widal test?
Widal test should be performed after first week of fever. The reason being,the antibodies against “O” and “H” antigens of Salmonella, start appearing in the blood of patients by the end of 1st week, with sharp rise in 2nd and 3rd week and the antibody titre remains steady till 4th week after which it starts declining. It is preferable to test two blood samples at an interval of 7 to 10 days to demonstrate a rising antibody titres.