Evaluation of widal tube dilution and enzyme-linked immunosorbent assay for diagnosing typhoid fever at a referral hospital in Kenya

Abstract

Background: Typhoid fever is a disease caused by the pathogen Salmonella enterica serotype typhi. It is a water and food-borne disease of public health importance. To diagnose typhoid fever, Kenyan health facilities have relied on the Widal slide test, a serological technique. The documented Sensitivity and Specificity values of the Widal slide test are inconsistent ranging from 34-86% and 42-99% respectively. In 2011 in Kenya, the Ministry of Health banned the use of the Widal slide test for diagnosing typhoid fever in health facilities because of its poor performance. This was in accordance with the set World Health Organization guidelines, which stipulate that the sensitivity and specificity values of a test should approach 100% and should be consistent. To replace the Widal slide test in routine diagnosis of typhoid fever, WHO recommends the Widal tube dilution test, which is a more accurate version of the Widal slide test. Apart from that, use of culture to diagnose typhoid fever is also recommended. However, these tests present challenges in terms of speed and cost. Thus, there was need to evaluate other existing tests, which are cheaper and faster. Objective: To analyze the value of the Widal tube dilution test vis-à-vis the Enzyme- Linked Immunosorbent Assay (IgG) in diagnosis of typhoid fever. Setting Design and Methodology: The study was cross-sectional, done at the Moi Teaching and Referral Hospital outpatient clinic and the wards. Calculation of sample size arrived at a minimum of 118 clinically suspected cases using a formula derived from Fischer’s formula for use in Sensitivity and Specificity studies. Convenience sampling was used to select the participants. Only willing cases were enrolled in the study. Participants were both males and females of all ages. Blood cultures were done using venous blood of all the participants. The Widal tube dilution test and Enzyme-Linked Immunosorbent Assay (IgG) were performed using prepared serum of all the participants. Culture, Widal tube dilution, and ELISA (IgG) test results were analyzed to determine any variation in the tests. Ethical Considerations: Permission to conduct the study was sought and granted from the Institutional Research and Ethics Committee and Moi Teaching and Referral Hospital. Results: Widal tube dilution test had a sensitivity of 76.92%, specificity of 77.36%, Positive Predictive Value of 80.65%, and Negative Predictive Value of 73.21%. The test was easy to perform and cost-effective when compared to culture. However, it lacked in speed and in Negative Predictive Value. The ELISA (IgG) test had higher sensitivity (87.69%), specificity (92.45%), Positive Predictive Value (93.44%) and Negative Predictive Value (85.96%). It was fast, easy to perform, and cheap when compared to culture. Conclusion and Recommendations: The study showed ELISA (IgG) to be a practical alternative to the Widal slide test. It had higher specificity and sensitivity values than the Widal tube dilution test. It is cost effective, fast, and easy to perform as compared to culture. The cost per patient for ELISA (IgG) amounted approximately $5. It should be considered for use in routine diagnosis of typhoid fever in health facilities.