Sensitivity and Specificity of Vi-Indirect Fluore scent Antibody Test in Diagnosis of Typhoid Fever

Chang, Kyung Hee; Rhyoo, Dong Yeul; Park, Sung Ha; Park, Byung Kyu; Lee, Joon Ku; Yeom, Jun Sup; Choi, Young Hwa; Song, Young Gu; Kim, Hyun Sook; Chong, Yun Sop; Kim, June Myung

Abstract

BACKGROUND
Typhoid fever is diagnosed by culture or serological study. The confirmative diagnosis of typhoid fever is made by culture of the causative orga-nism usually from body fluids. Serological test is a supportive diagnostic tool, which is useful for early dia-gnosis. In Severance Hospital, Vi-indirect fluorescent antibody test(Vi-IFAT) using the Vi-antigen of Salmo-nella typhi has been used in the diagnosis of typhoid fever since 1989. We investigated the test results from the past 7 years, in order to clarify the sensitivity and specificity of Vi-IFAT.
METHODS
A retrospective study was done on pa-tients whose chief complaint was fever and who were tested using Vi-IFAT in the Severance Hospital from 1989 to 1996. The positive value for Vi-IFAT was de- fined as 1:64 or higher.
RESULTS
The sensitivity and specificity of Vi-IFAT for typhoid fever was 94.4% and 95.1%, respectively. The positive and negative predictive values were 85.7% and 98.2% respectively. Positive rates of Vi-IFAT after fever onset increased with time and 68% were positive before the first week. From the first to the second week, 89.5% were positive and after the second week, 100% were positive.
CONCLUSION
Vi-IFAT is not only a valuable sero-logic test for the diagnosis of typhoid fever, but also useful in the early diagnosis of the disease.