Rapid Immunochromatographic Assay of IgM Antibodies to Salmonella Typhi in Diagnosis of Typhoid Fever in Adults

Abstract

Enteric fever is a potentially severe systemic febrile illness that is usually presented with non- specific symptoms and signs such as slow gradually progressive fever, nausea, vomiting, abdominal pain, malaise, headache, constipation then bloody diarrhea and hepatospleenomegally (Clark et al; 2010). Microbiologic culture of a blood sample is considered to be the golden test for the diagnosis of typhoid fever even though it takes up to seven days and requires a well equipped laboratory (Parry et al; 2002). Serological diagnosis using Widal test provides a cost and time efficient alternative for blood culture, however its performance remains unsatisfying with sensitivity reported from Egypt of 77% using blood culture as a gold standard test and with the need for establishment of a local cut off titer prior to use which makes its interpretation more complicated (Wilke et al; 2002). Assays that detect IgM antibodies to S. Typhi which develop early in acute typhoid fever suggesting current infection are more sensitive and specific than the Widal test, and can be performed more rapidly. In the absence of culture facilities, IgM antibody tests are more useful than Widal test in diagnosis of typhoid fever in endemic areas (Cheesbrough; 2006).

The aim of the present study was to Evaluate the Enterocheck WB® test (a rapid, qualitative, Immunochromatographic assay for the detection of IgM antibodies to S. typhi in human serum/plasma or whole blood specimen), in comparison to Widal test as a rapid diagnostic tool for typhoid fever in adults. The present study was conducted on 154 patients clinically suspected as typhoid and 46 healthy controls. The patients were divided according to blood culture results into 2 groups; Group I comprised 21/200 (14%) patients with positive blood culture for S.typhi. Group II included 133/200 (86%) patients with negative blood culture results. Blood samples were collected from the patients to perform blood cultures, Widal test and Enterocheck test as well as from controls to perform Widal test and Enterocheck test. Blood culture showed only 21/200 positive cases (14%). When considering O and H titer ≥160 as positive, Widal test showed 59/200 (72.2%) positive cases, the sensitivity and specificity of Widal were 80.95% and 70.67% respectively. Eighteen cases out of 200 representing 95% of the studied subjects were positive using Enterocheck test and the sensitivity and specificity of this test were 86% and 89%, respectively.