Clinical Evaluation of a Multiplex PCR for the Detection of Salmonella enterica Serovars Typhi and Paratyphi A from Blood Specimens in a High-Endemic Setting.


Stephane Pouzol, Arif Mohammad Tanmoy, Dilruba Ahmed, Farhana Khanam, W. Abdullah Brooks,Golam Sarower Bhuyan, Laetitia Fabre, Juliet E. Bryant, Marie-Paule Gustin, Philippe Vanhems, Bill Carman, François-Xavier Weill, Firdausi Qadri, Samir Saha and Hubert Endtz


Enteric fever is a major public health concern in endemic areas, particularly in infrastructure-limited countries where  Paratyphi A has emerged in increasing proportion of cases. We aimed to evaluate a method to detect Typhi ( Typhi) and  Paratyphi A ( Paratyphi) in febrile patients in Bangladesh. We conducted a prospective study enrolling patients with fever > 38°C admitted to two large urban hospitals and two outpatient clinics located in Dhaka, Bangladesh. We developed and evaluated a method combining short culture with a new molecular assay to simultaneously detect and differentiate  Typhi and  Paratyphi A from other  directly from 2 to 4 mL of whole blood in febrile patients ( = 680). A total of 680 cases were enrolled from the four participating sites. An increase in the detection rate (+38.8%) in  Typhi and . Paratyphi A was observed with a multiplex polymerase chain reaction (PCR) assay, and absence of non-typhoidal  detection was reported. All 45 healthy controls were culture and PCR negative, generating an estimated 92.9% of specificity on clinical samples. When clinical performance was assessed in the absence of blood volume prioritization for testing, a latent class model estimates clinical performance ≥ 95% in sensitivity and specificity with likelihood ratio (LR) LR+ > 10 and LR− < 0.1 for the multiplex PCR assay. The alternative method to blood culture we developed may be useful alone or in combination with culture or serological tests for epidemiological studies in high disease burden settings and should be considered as secondary endpoint test for future vaccine trials.

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