The Widal test is one method that may be used to help make a presumptive diagnosis of enteric fever, also known as typhoid fever. Although the test is no longer commonly performed in the United States or other developed countries, it is still in use in many developing countries where enteric fever is endemic and limited resources require the use of rapid, affordable testing alternatives.
Enteric fever is a life-threatening illness caused by infection with the bacterium Salmonella enterica serotype Typhi (S. typhi), usually transmitted through food and drinks contaminated with fecal matter. It is associated with symptoms that include high fever, headache, abdominal pain, diarrhea, and a rash known as "rose spots." Early diagnosis and treatment are important because serious complications, including severe intestinal bleeding or perforation, can develop within a few weeks. The infection is rare in the US and other industrialized nations but is more common in developing countries, including India, parts of South, East and Southeast Asia, and countries in Africa, the Caribbean, Central and South America, and Eastern Europe. Cases of enteric fever in the US are usually attributed to travelers to these endemic areas.
Developed in 1896 and named after Georges Ferdinand Widal, who introduced it, the method relies on a reaction in a test tube or on a slide between antibodies present in the infected person's blood sample and specific antigens of S. typhi, which produces clumping (agglutination) that is visible to the naked eye. While the method is easy to perform, concerns remain about the reliability of the Widal test and studies of the assay's sensitivity and other measures of reliability have been disappointing. Besides cross-reactivity with other Salmonella species, the test cannot distinguish between a current infection and a previous infection or vaccination against typhoid.
In the US and other industrialized nations, testing for enteric fever usually involves a blood culture to detect the bacteria during the first week of fever. A stool, urine or bone marrow culture may also be performed. A blood culture, however, can be labor- and time-intensive in areas of the world that lack the resources for automated equipment. In developing countries, such as those in Africa, the Widal test continues to be used instead of cultures because it is quicker, simpler, and less costly to perform.
The World Health Organization (WHO) has said that due to the various factors that can influence the results of a Widal test, it is best not to rely too much on this test. WHO instead recommends the use of cultures whenever possible. Until another simple, inexpensive, and reliable option becomes available, however, use of the Widal test will probably persist in those countries with limited resources. Research is being conducted on a different blood test called Typhidot-M that produces results in one hour, appears to have greater reliability, and may be an alternative for the Widal test in the early diagnosis of enteric fever.