Typhidot test: Developed in Malaysia, detects both IgM and IgG against a 50 KD Antigen of Salmonella typhi. It takes 3 hours to perform. Multinational clinical evaluation suggests that it is a simple, rapid, economic test with high specific (75%), sensitive (95%) and high negative and positive predictive values.
Limitations: In endemic areas after the age of 2 years after typhoid infection, IgG antibodies are formed so this test cannot differentiate acute and convalescent cases. It may give false positive results because of previous infection with S. typhi or current re-infection in which secondary immune response significantly boosts (augments) IgG production and IgM becomes undetectable. To increase the diagnostic efficacy a modified version of typhidot has been developed, called as Typhidot-M in which IgG is totally inactivated in the serum sample and only IgM is detected. Trials showed that it is better than Widal and blood culture methods. It may prove very useful in areas of high endemicity of typhoid fever and has potential to replace Widal test because of its rapidity, and accuracy in diagnosis of typhoid fever. Typhidot was recently evaluated in Vellore and it showed 100% sensitivity and 80% specificity when bacteremic patients were analysed.