Enteric Fever in a Cross-section of Patients in Karachi: Current Correlation of Positive Blood Cultures with the Widal Agglutination and the Typhidot Immunoassay Tests

Objectives: A lab-based scrutiny to assess the correlation of current blood culture Salmonella isolates as the gold standard with matched Widal agglutinin titers and the EIA-based Typhidot immunoassay antibodies. Methods: 2,704 blood specimens were drawn for culture and Widal test in a private clinical lab in Karachi City from subjects presenting with clinical signs of Enteric fever during April 2012 and March 2013. Of these, 1,497 yielded Salmonella isolates; sera of these patients that were not accompanied with requests for Typhidot were also subjected to dot immunoassay with informed consent solicited at the time of bleeding. All sera were stored at 40C until screened. Results: Blood from 802 males (53.6%) and 695 females (46.4%) yielded 61.85% S typhi (n=926), 31.26% S. paratyphi-A (n=468) and 6.88% S. paratyphi-B (n=103) isolates. Widal agglutinins were detected in 473 (31.5%) of the sera of these subjects. ‘H’ titers of 1:80 (n=264: 17.6%) without detectable ‘O’ antibodies were seen more frequently in children’s sera (n=112; 7.4%). Widal ‘H’ with ‘O’ agglutinins were recorded in 209 (13.9%) of corresponding positive blood cultures, of which 104 (6.9%) yielded titers of 1:320 or more. A total of 1,024 sera (58.4%) lacked detectable Widal antibodies. The Typhidot immunoglobulin dots, negative in 856 sera (57.1%), were detected in 641 specimens (42.8%).