ABSTRACT
BACKGROUND: Globally, there are an estimated 22 million cases of Salmonella enterica serovar Typhi infection each year. However, this figure is likely to be an underestimate due to the low sensitivity of blood culture in S. Typhi diagnosis. The aim of this study was to diagnose S. Typhi by conventional polymerase chain reaction (PCR) using patient's blood preserved with ethylenediamine tetraacetic acid (EDTA). METHODS: From April 2012 to September 2013, typhoid fever surveillance was conducted in Polesgo and Nioko, 2 dry slum areas in Ouagadougou, Burkina Faso. Blood culture was performed for febrile patients using an automated blood culture system. Additional blood was collected in EDTA tubes from those patients and preserved at -80°C. DNA was extracted from EDTA blood and PCR was performed to identify presence of S. Typhi. Randomly selected PCR products were further sequenced to identify S. Typhi-specific amplicons. RESULTS: Of 1674 patients, S. Typhi was isolated from 18 (1.1%) individuals by blood culture. EDTA blood was collected from 1578 patients, of which 298 EDTA samples were tested by PCR. Salmonella Typhi-specific DNA was identified in 44 (14.8%) samples. The sensitivity of S. Typhi-specific PCR from EDTA blood was 89% (74%-100%) among the blood culture-positive cases. Sixteen S. Typhi-positive PCR products were sequenced, and 13 retrieved the sequence of a S. Typhi-specific amplicon. CONCLUSIONS: These findings suggest that blood culture-based diagnoses of S. Typhi underestimate the burden of typhoid fever in Burkina Faso. PCR could be considered as an alternative method for the identification and diagnosis of S. Typhi in blood samples.
Subject(s)
Bacteremia/diagnosis , DNA, Bacterial/blood , Polymerase Chain Reaction/methods , Salmonella typhi/genetics , Typhoid Fever/diagnosis , Adolescent , Adult , Bacteremia/blood , Bacteremia/complications , Bacteremia/microbiology , Burkina Faso , Child , Child, Preschool , Cohort Studies , Edetic Acid , Female , Fever/etiology , Humans , Infant , Infant, Newborn , Male , Molecular Typing/methods , Public Health Surveillance , Typhoid Fever/blood , Typhoid Fever/complications , Typhoid Fever/microbiology , Young AdultABSTRACT
BACKGROUND: Salmonella enterica serovar Typhi is a predominant cause of bloodstream infections in sub-Saharan Africa (SSA). Increasing numbers of S. Typhi with resistance to ciprofloxacin have been reported from different parts of the world. However, data from SSA are limited. In this study, we aimed to measure the ciprofloxacin susceptibility of S. Typhi isolated from patients with febrile illness in SSA. METHODS: Febrile patients from 9 sites within 6 countries in SSA with a body temperature of ≥38.0°C were enrolled in this study. Blood samples were obtained for bacterial culture, and Salmonella isolates were identified biochemically and confirmed by multiplex polymerase chain reaction (PCR). Antimicrobial susceptibility of all Salmonella isolates was performed by disk diffusion test, and minimum inhibitory concentrations (MICs) against ciprofloxacin were measured by Etest. All Salmonella isolates with reduced susceptibility to ciprofloxacin (MIC > 0.06 µg/mL) were screened for mutations in quinolone resistance-determining regions in target genes, and the presence of plasmid-mediated quinolone resistance (PMQR) genes was assessed by PCR. RESULTS: A total of 8161 blood cultures were performed, and 100 (1.2%) S. Typhi, 2 (<0.1%) Salmonella enterica serovar Paratyphi A, and 27 (0.3%) nontyphoid Salmonella (NTS) were isolated. Multidrug-resistant S. Typhi were isolated in Kenya (79% [n = 38]) and Tanzania (89% [n = 8]) only. Reduced ciprofloxacin-susceptible (22% [n = 11]) S. Typhi were isolated only in Kenya. Among those 11 isolates, all had a Glu133Gly mutation in the gyrA gene combined with either a gyrA (Ser83Phe) or gyrB mutation (Ser464Phe). One Salmonella Paratyphi A isolate with reduced susceptibility to ciprofloxacin was found in Senegal, with 1 mutation in gyrA (Ser83Phe) and a second mutation in parC (Ser57Phe). Mutations in the parE gene and PMQR genes were not detected in any isolate. CONCLUSIONS: Salmonella Typhi with reduced susceptibility to ciprofloxacin was not distributed homogenously throughout SSA. Its prevalence was very high in Kenya, and was not observed in other study countries. Continuous monitoring of antimicrobial susceptibility is required to follow the potential spread of antimicrobial-resistant isolates throughout SSA.
