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Original Articles
Sensitivity and Specificity of Vi-Indirect Fluorescent Antibody Test in Diagnosis of Typhoid Fever
Chang KH, Rhyoo DY, Park SH, Park BK, Lee JK, Yeom JS, Choi YH, Song YG, Kim HS, Chong YS, Kim JM
Department of Internal Medicine, College of Medicine, Yonsei University, Seoul, Korea. Department of Clinical Pathology, College of Medicine, Yonsei University, Seoul, Korea.
Vol.30 Num.4 (p379~384)
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.
Keywords : Vi-antigen, Typhoid fever, Immunofluorescent antibody test