Performance of TUBEX® TF IgM Antibody Test Against Culture to Detect Typhoid Fever Among Hospitalized Patients in Nairobi County

Typhoid fever has remained endemic and a major health problem in developing countries like Kenya due to poor sanitation, overcrowding and limited access to diagnostic services. The main aim of this study was to determine the diagnostic value of TUBEX® TF IGM antibody tests for early diagnosis of typhoid fever among hospitalized patients in Nairobi County. TUBEX® TF is a competitive immunoassay which detects presence of anti-09 IgM Salmonella Typhi antibodies in a patient’s serum. We studied TUBEX® TF a rapid sera diagnostic test for its usefulness in early diagnosis of typhoid fever and we compared its sensitivity and specificity to that of Widal test. The study was conducted on 92 (Gp-I) febrile patients who had clinically suggestive signs and symptoms of typhoid fever. Two groups of controls were created; 45 (Gp-II) and 15 (Gp-III) age and sex matched febrile and healthy controls, respectively.  Blood culture was performed in all cases while TUBEX® TF and Widal tests were performed in both cases and controls. The sample size was based on convenience at the two health facilities of our study. Gp-I had 9 (9.78%) blood culture positives for S.Typhi, 11(11.99%) were positive for TUBEX® TF while 17 (18.48%) were positive for Widal test. 3 (6.67%) Gp-II were positive on both TUBEX® TF and Widal test while none of the two tests tested positive on Gp-III. Among 9 culture positive cases, TUBEX® TF was positive in 8 cases same as Widal test with sensitivity, specificity, PPV and NPV values of 88.9% (95% CI: 51.18-99.7), 97.6% (95% CI: 91.6-99.7), 80.0 %(95% CI: 44.4-97.5), 98.8 %(95% CI: 93.4-100), respectively. Widal test had 88.89% (95% CI: 51.8-99.7), 90.4% (95% CI: 81.9-95.7), 50.00% (95% CI: 24.7-75.3), 98.7% (95% CI: 92.9-100) respectively. This study demonstrated better results with TUBEX® TF test compared to Widal test when blood culture was used as a gold standard. However, these results should be further confirmed by using multiple gold standard tests such as molecular and enzyme-linked immunosorbent assays and carried out on large scale cross-sectional studies with varied prevalence of typhoid fever in the population. Keywords: Typhoid fever, TUBEX® TF, Widal, Cases and Controls. DOI: 10.7176/JBAH/9-4-0

Relationship between Antibody Susceptibility and Lipopolysaccharide O-Antigen Characteristics of Invasive and Gastrointestinal Nontyphoidal Salmonellae Isolates from Kenya

Background: Nontyphoidal Salmonellae (NTS) cause a large burden of invasive and gastrointestinal disease among young children in sub-Saharan Africa. No vaccine is currently available. Previous reports indicate the importance of the O-antigen of Salmonella lipopolysaccharide for virulence and resistance to antibody-mediated killing. We hypothesised that isolates with more O-antigen have increased resistance to antibody-mediated killing and are more likely to be invasive than gastrointestinal. Methodology/Principal findings: We studied 192 NTS isolates (114 Typhimurium, 78 Enteritidis) from blood and stools, mostly from paediatric admissions in Kenya 2000-2011. Isolates were tested for susceptibility to antibody-mediated killing, using whole adult serum. O-antigen structural characteristics, including O-acetylation and glucosylation, were investigated. Overall, isolates were susceptible to antibody-mediated killing, but S. Enteritidis were less susceptible and expressed more O-antigen than Typhimurium (p\u3c0.0001 for both comparisons). For S. Typhimurium, but not Enteritidis, O-antigen expression correlated with reduced sensitivity to killing (r = 0.29, 95% CI = 0.10-0.45, p = 0.002). Both serovars expressed O-antigen populations ranging 21-33 kDa average molecular weight. O-antigen from most Typhimurium were O-acetylated on rhamnose and abequose residues, while Enteritidis O-antigen had low or no O-acetylation. Both Typhimurium and Enteritidis O-antigen were approximately 20%-50% glucosylated. Amount of S. Typhimurium O-antigen and O-antigen glucosylation level were inversely related. There was no clear association between clinical presentation and antibody susceptibility, O-antigen level or other O-antigen features. Conclusion/Significance: Kenyan S. Typhimurium and Enteritidis clinical isolates are susceptible to antibody-mediated killing, with degree of susceptibility varying with level of O-antigen for S. Typhimurium. This supports the development of an antibody-inducing vaccine against NTS for Africa. No clear differences were found in the phenotype of isolates from blood and stool, suggesting that the same isolates can cause invasive disease and gastroenteritis. Genome studies are required to understand whether invasive and gastrointestinal isolates differ at the genotypic level

Molecular Surveillance Identifies Multiple Transmissions of Typhoid in West Africa.

BACKGROUND: The burden of typhoid in sub-Saharan African (SSA) countries has been difficult to estimate, in part, due to suboptimal laboratory diagnostics. However, surveillance blood cultures at two sites in Nigeria have identified typhoid associated with Salmonella enterica serovar Typhi (S. Typhi) as an important cause of bacteremia in children. METHODS: A total of 128 S. Typhi isolates from these studies in Nigeria were whole-genome sequenced, and the resulting data was used to place these Nigerian isolates into a worldwide context based on their phylogeny and carriage of molecular determinants of antibiotic resistance. RESULTS: Several distinct S. Typhi genotypes were identified in Nigeria that were related to other clusters of S. Typhi isolates from north, west and central regions of Africa. The rapidly expanding S. Typhi clade 4.3.1 (H58) previously associated with multiple antimicrobial resistances in Asia and in east, central and southern Africa, was not detected in this study. However, antimicrobial resistance was common amongst the Nigerian isolates and was associated with several plasmids, including the IncHI1 plasmid commonly associated with S. Typhi. CONCLUSIONS: These data indicate that typhoid in Nigeria was established through multiple independent introductions into the country, with evidence of regional spread. MDR typhoid appears to be evolving independently of the haplotype H58 found in other typhoid endemic countries. This study highlights an urgent need for routine surveillance to monitor the epidemiology of typhoid and evolution of antimicrobial resistance within the bacterial population as a means to facilitate public health interventions to reduce the substantial morbidity and mortality of typhoid

Phylogeographical analysis of the dominant multidrug-resistant H58 clade of Salmonella Typhi identifies inter- and intracontinental transmission events.

The emergence of multidrug-resistant (MDR) typhoid is a major global health threat affecting many countries where the disease is endemic. Here whole-genome sequence analysis of 1,832 Salmonella enterica serovar Typhi (S. Typhi) identifies a single dominant MDR lineage, H58, that has emerged and spread throughout Asia and Africa over the last 30 years. Our analysis identifies numerous transmissions of H58, including multiple transfers from Asia to Africa and an ongoing, unrecognized MDR epidemic within Africa itself. Notably, our analysis indicates that H58 lineages are displacing antibiotic-sensitive isolates, transforming the global population structure of this pathogen. H58 isolates can harbor a complex MDR element residing either on transmissible IncHI1 plasmids or within multiple chromosomal integration sites. We also identify new mutations that define the H58 lineage. This phylogeographical analysis provides a framework to facilitate global management of MDR typhoid and is applicable to similar MDR lineages emerging in other bacterial species

Distinct Salmonella Enteritidis lineages associated with enterocolitis in high-income settings and invasive disease in low-income settings.

An epidemiological paradox surrounds Salmonella enterica serovar Enteritidis. In high-income settings, it has been responsible for an epidemic of poultry-associated, self-limiting enterocolitis, whereas in sub-Saharan Africa it is a major cause of invasive nontyphoidal Salmonella disease, associated with high case fatality. By whole-genome sequence analysis of 675 isolates of S. Enteritidis from 45 countries, we show the existence of a global epidemic clade and two new clades of S. Enteritidis that are geographically restricted to distinct regions of Africa. The African isolates display genomic degradation, a novel prophage repertoire, and an expanded multidrug resistance plasmid. S. Enteritidis is a further example of a Salmonella serotype that displays niche plasticity, with distinct clades that enable it to become a prominent cause of gastroenteritis in association with the industrial production of eggs and of multidrug-resistant, bloodstream-invasive infection in Africa.This work was supported by the Wellcome Trust. We would like to thank the members of the Pathogen Informatics Team and the core sequencing teams at the Wellcome Trust Sanger Institute (Cambridge, UK). We are grateful to D. Harris for work in managing the sequence data

An extended genotyping framework for Salmonella enterica serovar Typhi, the cause of human typhoid.

The population of Salmonella enterica serovar Typhi (S. Typhi), the causative agent of typhoid fever, exhibits limited DNA sequence variation, which complicates efforts to rationally discriminate individual isolates. Here we utilize data from whole-genome sequences (WGS) of nearly 2,000 isolates sourced from over 60 countries to generate a robust genotyping scheme that is phylogenetically informative and compatible with a range of assays. These data show that, with the exception of the rapidly disseminating H58 subclade (now designated genotype 4.3.1), the global S. Typhi population is highly structured and includes dozens of subclades that display geographical restriction. The genotyping approach presented here can be used to interrogate local S. Typhi populations and help identify recent introductions of S. Typhi into new or previously endemic locations, providing information on their likely geographical source. This approach can be used to classify clinical isolates and provides a universal framework for further experimental investigations

SBA results of STm and SEn isolates with Malawi serum pool.

<p>Bacterial colony forming units (CFU) were counted at time 0 (T0) and after 3 h (T180) incubation of bacteria in 45 μL undiluted serum (final bacterial concentration 1×10⁶ CFU/ml). Killing/growth was determined by Log₁₀ (CFU at T180)-Log₁₀ (CFU at T0). Strains that could grow (Log₁₀ change >0) were considered “resistant”, strains that were killed (Log₁₀ change <0) were considered susceptible. Dashed/continuous line indicates median Log₁₀ change of STm (-2.9) and SEn (-1.2) isolates, respectively.</p

Correlation of SBA results (a, c) and OAg production levels (b, d) in <i>S</i>. Typhimurium (a, b) and <i>S</i>. Enteritidis (c, d) isolates with clinical presentations.

<p>Samples for which no clinical presentation was determined were excluded from analysis. Malawi serum pool was used for SBA. Invasive: <i>Salmonella</i> isolates from blood, urine, CSF. Gastrointestinal: <i>Salmonella</i> isolates from stools. Controls: <i>Salmonella</i> isolates from stools of healthy controls.</p