Pattern of widal agglutination reaction in apparently healthy population of Jimma town, southwest Ethiopia.
BACKGROUND
Typhoid fever is leading cause of morbidity in developing countries including Ethiopia. Isolation of Salmonella Typhi by culturing, from blood or other source, is the surest way of making laboratory diagnosis. However, in resource-limited countries, the Widal agglutination test provides cheaper and easy alternatives, though inappropriate technique and interpretation continue to cast a shadow on its usefulness.


METHODS
A cross-sectional study was carried out during the period of February to May 2004 to determine the baseline antibody tube titration and slide agglutination pattern to Widal antigen and the usefulness of rapid slide agglutination test for diagnostic purposes among apparently healthy population of Jimma town, southwest Ethiopia. Blood samples were collected from subjects who gave their consents after thorough explanation of the procedure and the purpose of the study. The study participants were selected by a systematic random sampling technique. The sera of subjects were tested for Widal agglutination by an experienced laboratory technologist according to the standard procedural protocol-using antigen from Chronolab AG, Switzerland Data were cleaned edited and entered in to a computer and analyzed using SPSS for window version 11.0. Major results were expressed as 95% probability limit, and validity scoring; agreement test (Kappa) was determined.


RESULTS
The result indicated that among the apparently health population, almost all the blood tested showed some titer of the antibody and reactivity of agglutination slide tests. The 95% probability limit (mean + 2SD) for anti H and anti O antigen titration was 1:276.89 and 1:207.89, respectively. These figures are closer to a cut-off titer of 1.320. There was a fair agreement between slide agglutination test and tube titer for 0 antigen (Kappa=0.225) and a poor agreement for H antigen (Kappa=0.066). When agglutination test result of highly reactive (+4) and titration of 1:320 were used, few cases became reactive indicating the need to raise the cut-off value to these points respectively.


CONCLUSIONS
It is recommended that if Widal test is to be used for the clinical work up of typhoid fever in adult population, a cut-off value highly reactive (+4),for rapid slide agglutination and a titer of 1.320 and above for tube titration test be used. At the cut-off values indicated above, Widal test has low sensitivity and positive predictive value and high specificity and negative predictive values. This makes the test useful support to clinical suspicion but unlikely means ofJscreening.
Mamo
Yoseph
Y
Department of Internal Medicine, Faculty of Medical Sciences, Jimma University.
Belachew
Tefera
T
Abebe
Woldecherkos
W
Gebre-Selassie
Solomon
S
Jira
Chali
C
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000372:Agglutination Tests / Q000379:methods; D000942:Antigens, Bacterial / Q000276:immunology*; D004522:Educational Status; D005002:Ethiopia; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012485:Salmonella typhi / Q000276:immunology*; D014435:Typhoid Fever / Q000097:blood / Q000276:immunology*
D000942:Antigens, Bacterial