A Comparative Study of Blood Culture and Widal Test in the Diagnosis of Typhoid Fever in Febrile Patients
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Date
2011-06
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Addis Ababa University
Abstract
Introduction: Typhoid fever is a major health problem in developing countries. An accurate diagnosis on clinical grounds alone is difficult. In areas of endemicity, such as Ethiopia, bacterial culture facilities, definitive diagnosis for typhoid fever, are often unavailable. So, the Widal test has been in use as the diagnostic assay. However, the value of the test for the diagnosis of typhoid fever has been debated. So evaluating the result of Widal test is necessary for correct interpretation of the result. In addition typhoid fever caused by multidrug resistant strains of Salmonella typhi presents a serious problem in many developing countries.
Objective: The main objective of this study is to compare the result of Widal test and blood culture in the diagnosis of typhoid fever in febrile patients and to determine the antimicrobial pattern of isolates.
Methodology: Data was collected from 277 febrile patients with symptoms clinically similar to typhoid fever visiting St. Paul’s General Specialized Hospitals from mid December 2010 to March 2011. Blood was inoculated immediately after collection into 45ml of Trypton Soy Broth and further processed for the identification of S.typhi and S.paratyphi. Antimicrobial
susceptibility pattern of S. typhi and S. paratyphi isolates were determined by the modified Kirby-Bauer disk diffusion technique. Slide agglutination test as screening test and tube agglutination for the determination of antibody titer for reactive slide agglutinations samples have made. An antibody titer of ≥1:80 for anti TO and ≥1:160 for anti TH are taken as a cut of value to indicate recent infection of typhoid fever. Statistical software package for widows (SPSS version 16) was used for analysis of the data and p value ≤0.05 was taken as significance.
Result: A total of 277 febrile patients were recruited for this study, but data from 270 were analysed because the remaining seven patients have no full data to be processed. 186 (68.9 %) were females and 84 (31.1 %) were males. 7 (2.6%) cases of S. typhi and 4 (1.5%) cases of S. paratyphi were identified with the total prevalence of typhoid fever 4.1 %. The total number of patients who have indicative of recent infection by either of O and H antigens Widal test is 88 (32.6%). The sensitivity, specificity, PPV and NPV of Widal test are 71.4 %, 68.44%, 5.7% and 98.9% respectively. Most (3/7[42.9%]) of the isolated S.typhi are highly resistant to amoxicillin. All species are sensitive for norfloxacin and ceftriaxone. S. paratyphi isolates show no resistance to gentamycine, tetracycline, norfloxacin and ciprofloxacin. More resistance (3 out of 4) is observed in amoxicillin. One species of S.typhi and 2 species of S. paratyphi are multi drug resistant.
Conclusion and recommendation: Widal test have a low sensitivity, specificity and PPV, but it has good NPV which indicates that negative Widal test result have a good indication for the absence of the disease. Hence, physicians should not totally depend on Widal test for the diagnosis of typhoid fever and should use other alternative diagnostics such as clinical knowledge to differentiate from other febrile infections. Regarding drug resistance both S.
typhi and S. paratyphi showed high resistance for commonly used drugs against typhoid fever. Therefore, sensitivity test based prescription should be started to prevent the continuous drug resistance development.
Key words: Widal test, blood culture, antimicrobial resistance, sensitivity, specificity, positive predictive value, negative predictive value
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Keywords
Widal test, Blood culture, Antimicrobial resistance, Sensitivity, specificity