Diagnosis of enteric fever caused by Salmonella spp. in Vietnam by a monoclonal antibody-based dot-blot ELISA

Abstract

Enteric fever caused by Salmonella spp. is prevalent in Vietnam. None of the currently available diagnostic methods meets the ideal criteria on rapidity, simplicity, sensitivity, specificity, cost-effectiveness and practicality for developing areas. In this study, a recently developed monoclonal antibody-based dot-blot ELISA was used in comparison with the hemoculture method and the classical Widal test for diagnosis of salmonellosis in 171 Vietnamese patients presenting with clinical features of enteric fever. Urine samples of 50 healthy counterparts were used as negative controls. Salmonella spp. were isolated from 77 of 171 patients (45%) while 98 and 111 patients were positive by dot-blot ELISA and Widal test, respectively. The diagnostic sensitivity, specificity, accuracy, positive predictive value and negative predictive value of the ELISA performed on three serial urine samples collected at 2 hour intervals of the 171 patients were 92.2%, 71.3%, 80.7%, 72.4% and 91.8%, respectively when compared with the culture method. The Widal test performed on acute and convalescence serum samples showed 87.0%, 46.8%, 68.4%, 60.4% and 83.3% diagnostic sensitivity, specificity, accuracy, and positive and negative predictive values, respectively when compared with the bacterial culture method. Kappa coefficience revealed very good agreement beyond chance between the MAb-based ELISA and the culture method. The ELISA was not reactive when tested on urine samples of 50 healthy individuals which indicates 100% specificity. The Salmonella antigenuria of the patients as detected by ELISA lasted 10.3 ± 3.9 days after initiating antibiotic treatment. The MAb-based dot-blot ELISA is easy to perform. It is rapid, sensitive, specific, inexpensive, and non-invasive and does not require equipment, thus is suitable for developing areas. It can detect acute/ recent infection and can be used for evaluation of the efficacy of the treatment.