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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. |
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