The utility of diagnostic tests for enteric fever in endemic locations

Abstract

Enteric fever, an infection caused by Salmonella enterica serovar Typhi and serovar Paratyphi A, is common and endemic in many areas of the Asian and African continents. In endemic areas, diagnostic tests are needed to diagnose acute cases for clinical management, to detect convalescent and chronic fecal carriage and for contact tracing. A suitable test may also allow an assessment of disease burden in a community to determine the need for vaccination programs. Each specific role may warrant a dedicated test, utilizing different samples, targets and methods to serve their respective purpose. Current diagnostic methods are poor. Blood culture is insufficiently sensitive and technically demanding, and bone marrow culture, although more sensitive, is infrequently performed. Antibody- and antigen-detection tests lend themselves to point-of-care format but remain insufficiently sensitive and specific for this role. There are concerns about the sensitivity of nucleic acid amplification tests and they have not become widely adopted. However, new approaches using genomics, proteomics, transcriptomics, in vivo-induced antigen and immunoaffinity proteomics-based technologies are being employed to identify new antigens, gene targets and metabolic products that could be used as a basis for more effective diagnostic tests. If novel tests are to be credible and widely used they require rigorous evaluation in endemic areas in studies with appropriate selection of patients, adequate sample sizes and proper attention to a gold standard reference. Here, we discuss the range of methods currently used for diagnosing enteric fever in endemic locations and we suggest new technologies which may improve enteric fever diagnostics over the coming years.