Rapid diagnosis of typhoid from blood cultures

Image of Salmonella enterica, courtesy of the CDC

Cara N. Wilder, Ph.D.

Typhoid fever is a life-threatening illness caused by the Gram-negative bacterium, Salmonella enterica subsp. enterica serovar Typhi. This foodborne pathogen is commonly contracted though the consumption of food or water that has been handled by a person shedding S. Typhi, or through the contamination of these products with sewage. Once ingested, the bacteria will inhabit the intestinal tract and bloodstream, resulting in a variety of complications including high fever, stomach pains, septicemia, and death.

Typhoid fever is common throughout most of the developing world, particularly in parts of Asia, Africa, and Latin America. Unfortunately, a number of people within these countries do not have access to a reliable laboratory diagnosis as the appropriate clinical facilities and techniques are not available. Thus, there is an urgent need for an inexpensive, easy-to-use, portable technique that can rapidly and safely diagnose typhoid fever independent of a hospital setting.

In a recent study, Castonguay-Vanier et al. investigated the accuracy and efficacy of a technique combining blood culture amplification of S. Typhi with a S. Typhi antigen rapid diagnostic test (RDT) developed by Standard Diagnostics (Cat. No. 15FK12). When tested against 23 Gram-negative reference pathogens, this assay was able to detect S. Typhi, as well as Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Ndolo. The precision of this assay was further analyzed through the examination of 6,456 blood cultures from 3,028 patients. From this prospective study, the group found that the sensitivity, negative predictive value, specificity, and positive predictive value were 96.7%, 99.5%, 97.9%, and 87.9%, respectively, for patients with proven S. Typhi bacteremia. Overall, these results suggest that the combination of blood culture amplification of S. Typhi with an S. Typhi RDT is promising as an effective, sensitive, and inexpensive tool for the rapid diagnosis of typhoid fever.

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