Welcome to Journal club Dr. Md. Abul Hossain Khan Honorary Trainee Department of microbiology, MMC A Comparative Study of Typhidot and Widal Test in Patients of Typhoid Fever

Introduction 1 Typhoid fever is a life threatening systemic infection occurring in developing areas of the world and a major public health problem. Annually at least 16 million new cases of typhoid globally and more than 13 million cases in Asia and causing more than six lakhs deaths worldwide. Blood culture and widal test are routinely employed investigations for diagnosis of typhoid fever in all clinical settings.

Introduction 2 Widal test has been used in the diagnosis of typhoid illness for long time in our country but it remains a serological test with a moderate sensitivity and specificity. Therefore, a reliable and easy to perform serodiagnostic test with a higher sensitivity and specificity than widal test is required for rapid diagnosis and management of typhoid cases & reducing morbidity and its complications.

Introduction 3 Typhidot is a rapid serological test for the diagnosis of typhoid fever. However, its specificity and sensitivity as compared to widal test has not been studied so far in our region. Few studies conducted in India and other parts of Asia have reported encouraging results. In view of this, the present study was conducted to know its utility and effectiveness in diagnostic yields as compared to widal test in this region.

Materials and Methods Typhidot test is a dot ELISA kit. The test is based on the presence of specific IgM and IgG antibodies to a specific 50KD OMP antigen of the Salmonella typhi. The typhidot test becomes positive within 2-3 days of infection and separately identifies IgM and IgG antibodies.

Interpretation of Typhidot A positive IgM was interpreted clinically as acute typhoidal illness While IgM and IgG positive were taken as acute typhoidal illness in middle stage of infection IgG positive was interpreted as chronic carrier or previous infection or reinfection.

Result In this study, 80 acute febrile illness patients were included and divided into 2 groups: - Group I: 56 patients with clinical diagnosis of typhoid fever and - Group II: 24 patients of suspected Non-typhoidal fever. Routine investigations(CBC, urine analysis and culture, CXR, LFTs), blood culture, widal test and tyhidot test were done in all patients. Results of blood culture, widal, and typhidot test were compared in all patients for their sensitivity and specificity.

Observations In group I: Blood culture was positive in 38, widal test was significance in 32 & typhidot tests were positive 44 out of 56 patients In group II: All were(24 patients) blood culture negative & 4 patients (17 %) were widal significance, while only 3 (12.5 %) tests were positive for typhidot.

Comparison of Blood culture, widal test and Typhidot TestTyphoid Cases (n = 56) Group I Non-typhoidal case (n=24) Group II Blood culture38(68%)0 widal test32(57%)4(17%) Typhidot44(79%)3(12.5%)

Comparison of Widal test and Typhidot tests in Culture Proven Cases and Non-Typhoid Cases. Test Culture Positive Typhoid Cases (n = 38 ) Non-Typhoid Case (n=24) Widal24(74%)4(17%) Typhidot35(92%)3(12.5%)

On comparative evaluation of widal test, typhidot and blood culture: Widal test: Sensitivity- 57% and specificity - 83%, Blood culture: Sensitivity- 68% and specificity-100% Typhidot test: Sensitivity-79 % and specificity-87.5% Amongst all the 38 patients in Group I, who were having positive blood culture, typhidot test was positive in 35 patients, giving a sensitivity of 92%, a specificity of 87.5% and a positive predictive value of 92% as compared to widal test which was positive in 28 patients with a sensitivity, specificity, positive predictive value of 74%, 83%, and 87.5% respectively.

Discussion Typhoid fever is a systemic illness with a significant morbidity and mortality in developing countries. Poor sanitation, overcrowding, low standard of living, lack of medical facilities,indiscriminate use of antibiotics and lack of vaccination lead to endemicity of typhoid fever and multi-resistant strains of Salmonella typhi in developing countries.

Discussion Blood culture has remained the gold standard test in diagnosis of typhoid fever, but its utility in early diagnosis is limited in early phase of illness thereby making the isolation of the organism difficult. Widal test has been used for over a century in developing countries for diagnosing typhoid fever but it has a low sensitivity, specificity and positive predictive value, which changes with the geographical areas.

Discussion Similar study carried out in the southern part of India reported typhidot of having a sensitivity of 100% and a specificity of 80% In another study group of typhoid patients in Pakistan, typhidot test had a comparable sensitivity of 94% and specificity of 77%, while widal test had a sensitivity and specificity of 63% and 83% only.

Discussion The effectiveness of typhidot test was also studied in two different studies in Malaysia. Its sensitivity and specificity was reported as 90.3% and 91.9% respectively in the first study and In second study, also showed a sensitivity and specificity of 98% and 76.6% respectively. Both the Malaysian studies showed it to be a better test in contrast to widal test for rapid diagnosis.

Conclusions Typhidot test is a highly sensitive and specific test in diagnosing typhoid fever. It is a rapid, easy to perform, more reliable test for typhoid fever as compared to widal test and can be useful in early institution of therapy. However, a larger prospective study would be required to fully evaluate the usefulness of this test in countries endemic to typhoid fever.