Recent advances in the rapid serodiagnosis of typhoid fever

Abstract

Development of a specific diagnostic test for typhoid requires the use of a specific antigen. The discovery of the specific 50kD antigen in the outer membrane of Salmonella typhi led to the development of a rapid dot EIA test (Typhidot™) to detect for the presence of specific IgM and IgG antibodies to the bacteria. Tfie test has a sensitivity of95%, a high negative predictive value and could produce results within 3 flours. The detection of IgM alone or with IgG would suggest acute typhoid while the detection of IgG only posed several interpretations such as convalescence or possible re-infection. Due to the lack of immunity to typhoid fever, patients in highly endemic areas often have re-infections. In the event of current re-infection, there will be a secondary immune response with a significant “boosting “ effect of IgG over IgM such that the latter could not be detected. A possible strategy to resolve this problem is to “unmask” the presence of IgM by removing total IgG. The development of a 3 hour IgM detection test (Typhidot-M ™) is useful in areas of high endemicity since it could differentiate new from convalescence cases. Data from studies to demonstrate the sensitivity, specificity and advantages of the various tests compared to conventional methods sliowed that the tests provided reliable alternatives to the Widal test.