Modifications In!uencing Widal Test Reactivity in a Novel Microplate Assay

Reliability of the Widal tube agglutination test has been the subject of many controversies over the years. !is study was performed to assess the e$ect of certain modifications on the performance of Widal test in a novel microplate assay. Sera from 37 patients (21 males; 16 females) (mean age 28 + 7 years) were tested in the Immunology Unit at King Khalid University Hospital, Riyadh. Among them were 26 patients with suspected typhoid fever and 11 had bacteriologically confirmed diagnosis of Salmonella infection. !e modifications included either the use of 0.5% bovine serum albumin (BSA), absorption of sera with sheep red blood cells (SRBC) or heat inactivation of sera. Compared with Widal tube agglutination test, microplate assay with SRBC absorption of the sera from patients with suspected typhoid fever was not only associated with enhancement of detection titers for both H (p < 0.001) and O (p < 0.005) Salmonella agglutinins but also the percentage of reactivity. !e presence of BSA augmented detection titers for Salmonella H agglutinins (p < 0.02) only. Heat inactivation of sera however was found to be associated with reduction in the detectable titers for both H (p < 0.03) and O (p < 0.01) agglutinins. Increased titers of Salmonella agglutinins were also evident in 11 patients with confirmed diagnosis of Salmonella infection. !e novel microplate agglutination assay using the SRBC absorption was associated with enhancement in Widal test reactivity and appears to be a useful alternative for the diagnosis of Salmonella infection. K e y w o r d s: Salmonella typhi, microplate agglutination assay, Salmonella agglutinins, Widal tube agglutination test * Corresponding author: Z. Shakoor, Department of Pathology, King Khalid University Hospital, King Saud University, Riyadh 11461, Kingdom of Saudi Arabia; phone: 00966-1-4671299; fax: 00966-1-4671842; e-mail: [email protected] Almogren A. et al. 2 138 agglutination test for detecting Salmonella agglutinins (Parry et al., 1999; Choo et al., 1993; Saha et al., 1996; Coovadia et al., 1986). Despite being used most frequently the specificity and sensitivity of the Widal test has been debated for many years, especially in the endemic areas where typhoid fever co-exists with non-typhoid febrile illnesses such as malaria and tuberculosis (Rai et al., 1989; Ghosh et al., 2001; Bakr et al., 2011; Keddy et al., 2011). Because of its limited diagnostic capability (Omuse et al., 2010) several modifications of the Widal test such as the slide agglutination test, (Ho$man et al., 1986) plate micro-agglutination test (Pang et al., 1983; Clegg et al., 1994; Barsoum and Awad, 1972), use of 2-mercaptoethanol for the detection of IgM (Jindal et al., 1992) and Salmonella para A, para B and Escherichia coli absorption (Rai et al., 1989) have been investigated but none of these could gain a reasonable acceptance. !e need for a tangible test for the diagnosis of Salmonella infection therefore remains (Baker et al., 2010) and this study examines the e$ect of certain modifications on the performance of Widal test.