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.
Posted by Tim Sandle
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