Evaluation of a Simple Blood Culture Amplification and Antigen Detection Method for Diagnosis of Salmonella enterica Serovar Typhi Bacteremia

Abstract

In most areas where typhoid is endemic, laboratory diagnosis is not possible due to the lack of appropriate facilities. We investigated whether the combination of blood culture amplification of Salmonella enterica serovar Typhi with an S. Typhi antigen rapid diagnostic test (RDT) could be an accurate and inexpensive tool for the accelerated diagnosis of patients with acute typhoid in Laos. For a panel of 23 Gram-negative reference pathogens, the Standard Diagnostics (catalog no. 15FK20; Kyonggi-do, South Korea) RDT gave positive results for S. Typhi NCTC 8385, S. Typhi NCTC 786 (Vi negative), Salmonella enterica serovar Enteritidis (ATCC 13076), and Salmonella enterica serovar Ndolo NCTC 8700 (all group D). In a prospective study of 6,456 blood culture bottles from 3,028 patients over 15 months, 392 blood culture bottles (6.1%) from 221 (7.3%) patients had Gramnegative rods (GNRs) seen in the blood culture fluid. 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 and 91.2%, 98.4%, 98.9%, and 93.9% for patients with group D Salmonella. The median (range) number of days between diagnosis by RDT and reference assays was 1 (؊1 to ؉2) day for those with confirmed S. Typhi. The use of antigen-based pathogen detection in blood culture fluid may be a useful, relatively rapid, inexpensive, and accurate technique for the identification of important causes of bacteremia in the tropics.

Typhoid in Laos: An 18-Year Perspective

“…9 A prospective study of the use of the rapid diagnostic test (RDT) (using OneStep Salmonella Typhi Ag Rapid Detection Kit; Standard Diagnostics, Kyonggi-do, South Korea) in Mahosot Hospital between September 2010 and December 2011 found S. Typhi in 30 (0.99%) of 3,028 blood cultures. 10 Subsequently, it was shown that gyrA mutations could be detected in RDTderived DNA to predict fluoroquinolone resistance in S. Typhi. 11 In a parallel article, we used data from sentinel surveillance from Mahosot Hospital over a 2-year period combined with a healthcare utilization survey in the hospital's main catchment area of Vientiane to develop an estimate of enteric fever incidence in the community.…”

Typhidot -a Blessing or a Menace

“… 8 , 9 Typhoid diagnosis in the tropics could be enhanced by making the identification of S. typhi in blood cultures simpler, less expensive, and faster. 10 …”

A Novel Technique for Detecting Antibiotic-Resistant Typhoid from Rapid Diagnostic Tests

“…We demonstrated the utility of an antigen-detecting S . Typhi rapid diagnostic test (RDT) performed with blood culture fluid containing Gram-negative rods (GNRs) in typhoid diagnosis ( 9 ). As DNA extracts from RDTs and dried blood spots have been used for molecular surveillance of malaria and HIV drug resistance ( 10 – 12 ), we hypothesized that mutations in the gyrA gene could be detected from S .…”