Genetic heterogeneity in the Salmonella Typhi Vi capsule locus: a population genomic study from Fiji.

Typhoid fever is endemic in many parts of the world and remains a major public health concern in tropical and sub-tropical developing nations, including Fiji. To address high rates of typhoid fever, the Northern Division of Fiji implemented a mass vaccination with typhoid conjugate vaccine (Vi-polysaccharide conjugated to tetanus toxoid) as a public health control measure in 2023. In this study we define the genomic epidemiology of Salmonella Typhi in the Northern Division prior to island-wide vaccination, sequencing 85% (n=419) of the total cases from the Northern and Central Divisions of Fiji that occurred in the period 2017-2019. We found elevated rates of nucleotide polymorphisms in the tviD and tviE genes (responsible for Vi-polysaccharide synthesis) relative to core genome levels within the Fiji endemic S. Typhi genotype 4.2. Expansion of these findings within a globally representative database of 12 382 S. Typhi (86 genotyphi clusters) showed evidence of convergent evolution of the same tviE mutations across the S. Typhi population, indicating that tvi selection has occurred both independently and globally. The functional impact of tvi mutations on the Vi-capsular structure and other phenotypic characteristics are not fully elucidated, yet commonly occurring tviE polymorphisms localize adjacent to predicted active site residues when overlayed against the predicted TviE protein structure. Given the central role of the Vi-polysaccharide in S. Typhi biology and vaccination, further integrated epidemiological, genomic and phenotypic surveillance is required to determine the spread and functional implications of these mutations.

Single and two-dose typhoid conjugate vaccine safety and immunogenicity in HIV-exposed uninfected and HIV-unexposed uninfected Malawian children.

Vaccine safety and immunogenicity data in human immunodeficiency virus (HIV)-exposed uninfected (HEU) children are important for decision-making in HIV and typhoid co-endemic countries. In an open-label study, we recruited Malawian HEU and HIV unexposed uninfected (HUU) infants aged 9 - 11 months. HEU participants were randomized to receive Vi-tetanus toxoid conjugate vaccine (Vi-TT) at 9 months, Vi-TT at 15 months, or Vi-TT at 9 and 15 months. HUU participants received Vi-TT at 9 and 15 months. Safety outcomes included solicited and unsolicited adverse events (AE) and serious AEs (SAEs) within 7 days, 28 days, and 6 months of vaccination, respectively. Serum was collected before and at day 28 after each vaccination to measure anti-Vi IgG antibodies by enzyme-linked immunosorbent assay (ELISA). Cohort 1 (66 participants) enrollment began 02 December 2019, and follow-up was terminated before completion due to the COVID-19 pandemic. Cohort 2 (100 participants) enrollment began 25 March 2020. Solicited AEs were mostly mild, with no significant differences between HEU and HUU participants or one- and two-dose groups. All six SAEs were unrelated to vaccination. Anti-Vi geometric mean titers (GMT) increased significantly from 4.1 to 4.6 ELISA units (EU)/mL at baseline to 2572.0 - 4117.6 EU/mL on day 28 post-vaccination, and similarly between HEU and HUU participants for both one- and two-dose schedules. All participants seroconverted (>4-fold increase in GMT) by the final study visit. Our findings of comparable safety and immunogenicity of Vi-TT in HUU and HEU children support country introductions with single-dose Vi-TT in HIV-endemic countries.

The use of controlled human infection models to identify correlates of protection for invasive Salmonella vaccines.

Controlled human infection model (CHIM) studies, which involve deliberate exposure of healthy human volunteers to an infectious agent, are recognised as important tools to advance vaccine development. These studies not only facilitate estimates of vaccine efficacy, but also offer an experimental approach to study disease pathogenesis and profile vaccine immunogenicity in a controlled environment, allowing correlation with clinical outcomes. Consequently, the data from CHIMs can be used to identify immunological correlates of protection (CoP), which can help accelerate vaccine development. In the case of invasive Salmonella infections, vaccination offers a potential instrument to prevent disease. Invasive Salmonella disease, caused by the enteric fever pathogens Salmonella enterica serovar Typhi (S. Typhi) and S. Paratyphi A, B and C, and nontyphoidal Salmonella (iNTS), remains a significant cause of mortality and morbidity in low- and middle-income countries, resulting in over 200,000 deaths and the loss of 15 million DALYs annually. CHIM studies have contributed to the understanding of S. Typhi infection and provided invaluable insight into the development of vaccines and CoP following vaccination against S. Typhi. However, CoP are less well understood for S. Paratyphi A and iNTS. This brief review focuses on the contribution of vaccine-CHIM trials to our understanding of the immune mechanisms associated with protection following vaccines against invasive Salmonella pathogens, particularly in relation to CoP.

Changes in monocyte subsets in volunteers who received an oral wild-type Salmonella Typhi challenge and reached typhoid diagnosis criteria.

An oral Controlled Human Infection Model (CHIM) with wild-type S. Typhi was re-established allowing us to explore the development of immunity. In this model, ~55% of volunteers who received the challenge reached typhoid diagnosis criteria (TD), while ~45% did not (NoTD). Intestinal macrophages are one of the first lines of defense against enteric pathogens. Most organs have self-renewing macrophages derived from tissue-resident progenitor cells seeded during the embryonic stage; however, the gut lacks these progenitors, and all intestinal macrophages are derived from circulating monocytes. After infecting gut-associated lymphoid tissues underlying microfold (M) cells, S. Typhi causes a primary bacteremia seeding organs of the reticuloendothelial system. Following days of incubation, a second bacteremia and clinical disease ensue. S. Typhi likely interacts with circulating monocytes or their progenitors in the bone marrow. We assessed changes in circulating monocytes after CHIM. The timepoints studied included 0 hours (pre-challenge) and days 1, 2, 4, 7, 9, 14, 21 and 28 after challenge. TD participants provided extra samples at the time of typhoid diagnosis, and 48-96 hours later (referred as ToD). We report changes in Classical Monocytes -CM-, Intermediate Monocytes -IM- and Non-classical Monocytes -NCM-. Changes in monocyte activation markers were identified only in TD participants and during ToD. CM and IM upregulated molecules related to interaction with bacterial antigens (TLR4, TLR5, CD36 and CD206). Of importance, CM and IM showed enhanced binding of S. Typhi. Upregulation of inflammatory molecules like TNF-α were detected, but mechanisms involved in limiting inflammation were also activated (CD163 and CD354 downregulation). CM upregulated molecules to interact/modulate cells of the adaptive immunity, including T cells (HLA-DR, CD274 and CD86) and B cells (CD257). Both CM and IM showed potential to migrate to the gut as integrin α4ß7 was upregulated. Unsupervised analysis revealed 7 dynamic cell clusters. Five of these belonged to CM showing that this is the main population activated during ToD. Overall, we provide new insights into the changes that diverse circulating monocyte subsets undergo after typhoid diagnosis, which might be important to control this disease since these cells will ultimately become intestinal macrophages once they reach the gut.

Prevalence of typhoid fever and its associated factors among febrile patients visiting Arerti Primary Hospital, Amhara Region, north east Ethiopia.

Background: Typhoid fever is one of the major public health concerns in developing countries, including Ethiopia. Understanding the burden and factors contributing to the transmission and development of the disease is crucial to applying appropriate preventive and therapeutic interventions. Objective: To assess the prevalence of typhoid fever and its associated factors among febrile patients visiting Arerti Primary Hospital from 1 March to 30 May 2022. Methods: A facility-based cross-sectional study was employed among 326 febrile patients visiting Arerti Primary Hospital for health services. The data were collected using laboratory procedures (widal test) and a structured interviewer-administered questionnaire. The data were entered using Epi Data version 3.1 and analyzed by SPSS version 25. Logistic regression was used to determine associations between variables. P-value < 0.05 and adjusted odds ratio with 95% confidence interval were used to measure the presence and strength of associations. Results: In this study, of the total 317 cases that participated, the majority (64.4%) of them were males with age ranges from 13 to 63 years. The overall prevalence of positive antigen tests for typhoid infection was 30.0% (95% CI: 25.0%-35.3%). About 66.9% of the study participants had good knowledge, 75.7% had favorable perception, and 42.3% had good infection prevention practice. Being unemployed [AOR = 7.57, 95% CI (1.98, 28.93)], being a farmer [AOR = 2.73, 95% CI (1.01, 7.41)], and having a body mass index (BMI) below 18.5 kg/m2 [AOR = 5.12, 95%CI (2.45, 10.68)] were significantly associated with typhoid fever infection. Conclusion: The prevalence of typhoid fever among febrile patients was high. Typhoid fever infection was significantly associated with occupational status (being unemployed and being a farmer) and lower BMI. The level of knowledge, perception, and practice of typhoid fever infection prevention were found inadequate. Therefore, behavioral change interventions are needed at the community level.

Ultrasound as a triaging tool for the diagnosis of malaria and typhoid in a resource constrained setting: A proposed frame-work.

INTRODUCTION: Ultrasound has proven to have great potentials in the diagnosis and work-up of patients affected by tropical diseases. Its role in the diagnosis of malaria and typhoid abounds, but its value as a triaging tool in a resource-constrained settings is indistinct. Our review aimed is aimed at assessing the utility of ultrasound in diagnosis and prognosis of malaria and typhoid. MATERIALS AND METHOD: Extensive literature search was conducted using the PubMed electronic database, for original peer reviewed articles in English language within 1964-2023. Keywords like "malaria", "typhoid", "S. Typhi", "Salmonella Typhi", "enteric fever", "ultrasound", "sonography" and "ultrasonography" were searched, using Boolean operators such as (OR, AND) applying the following filters (English, Human). A systematic synthesis of the literature was done. RESULT: Our initial search yielded 749 potentially relevant references out of which 55 were found to be eligible. Organs assessed include the liver, spleen, kidneys, intestines, mesenteric lymph nodes, among others. For malaria, pathognomonic conditions like splenic enlargement, hepatomegaly, renal abnormalities as well as mesenteric lymph nodes and intestinal wall thickening in patients with typhoid fever. CONCLUSION: Ultrasound by experienced clinicians adds significantly to the diagnosis and work-up of patients with malaria and typhoid fever. However, it is important to note that ultrasound alone may not be sufficient for definitive diagnosis as laboratory tests may still be required for confirmatory diagnosis. IMPLICATION FOR PRACTICE: This study provide information on ultrasound in diagnosis of Malaria and typhoid by evaluating the morphological changes in abdominal and other organs of the body. This can be a guide to clinicians and other healthcare providers for early diagnosis and work-up of patients in endemic areas where resources are scarce.

TolC facilitates the intracellular survival and immunomodulation of Salmonella Typhi in human host cells.

Salmonella enterica serovar Typhi (S. Typhi) causes typhoid fever, a systemic infection that affects millions of people worldwide. S. Typhi can invade and survive within host cells, such as intestinal epithelial cells and macrophages, by modulating their immune responses. However, the immunomodulatory capability of S. Typhi in relation to TolC-facilitated efflux pump function remains unclear. The role of TolC, an outer membrane protein that facilitates efflux pump function, in the invasion and immunomodulation of S. Typhi, was studied in human intestinal epithelial cells and macrophages. The tolC deletion mutant of S. Typhi was compared with the wild-type and its complemented strain in terms of their ability to invade epithelial cells, survive and induce cytotoxicity in macrophages, and elicit proinflammatory cytokine production in macrophages. The tolC mutant, which has a defective outer membrane, was impaired in invading epithelial cells compared to the wild-type strain, but the intracellular presence of the tolC mutant exhibited greater cytotoxicity and induced higher levels of proinflammatory cytokines (IL-1ß and IL-8) in macrophages compared to the wild-type strain. These effects were reversed by complementing the tolC mutant with a functional tolC gene. Our results suggest that TolC plays a role in S. Typhi to efficiently invade epithelial cells and suppress host immune responses during infection. TolC may be a potential target for the development of novel therapeutics against typhoid fever.

Dynamics and control of typhoid fever in Sheno town, Ethiopia: A comprehensive nonlinear model for transmission analysis and effective intervention strategies.

This study presents a reliable mathematical model to explain the spread of typhoid fever, covering stages of susceptibility, infection, carrying, and recovery, specifically in the Sheno town community. A detailed analysis is done to ensure the solutions are positive, stay within certain limits, and are stable for both situations where the disease is absent and where it is consistently present. The Routh-Hurwitz stability criterion has been used and applied for the purpose of stability analysis. Using the next-generation matrix, we determined the intrinsic potential for disease transmission. It showing that typhoid fever is spreading actively in Sheno town, with cases above a critical level. Our findings reveal the instability of the disease-free equilibrium point alongside the stability of the endemic equilibrium point. We identified two pivotal factors for transmission of the disease: the infectious rate, representing the speed of disease transmission, and the recruitment rate, indicating the rate at which new individuals enter the susceptible population. These parameters are indispensable for devising effective control measures. It is imperative to keep these parameters below specific thresholds to maintain a basic reproduction number favorable for disease control. Additionally, the study carefully examines how different factors affect the spread of typhoid fever, giving a detailed understanding of its dynamics. At the end, this study provides valuable insights and specific strategies for managing the disease in the Sheno town community.

Typhoid fever: the challenging diagnosis of a pseudo-outbreak in Benguet, Philippines.

Objective: The event-based surveillance and response report from the municipality of Buguias in the Philippines covering the period 1 January to 29 October 2022 indicated an unusual increase in the number of typhoid cases that surpassed the epidemic threshold for consecutive weeks. An investigation was conducted to confirm the existence of an outbreak, identify the source(s) of transmission and recommend prevention and control measures. Methods: The investigation employed a descriptive design. Medical records were reviewed to verify diagnoses and to identify cases that met case definitions. Key informant interviews were conducted to identify possible sources of transmission and investigate the reporting of cases in the Philippine Integrated Disease Surveillance and Response (PIDSR) system. Results: A total of 220 cases of typhoid fever were captured by the PIDSR system. Of the 208 suspected cases that were reviewed, only 15 (7.2%) met the case definition used in this investigation. Fourteen of these 15 verified cases were interviewed; five (35.7%) were farmers and 13 (92.8%) reported using springs as their main water source and source of drinking-water. Reporting of cases in the PIDSR system was largely based on the final chart diagnosis or a positive Typhidot or Tubex rapid diagnostic test result. The PIDSR case definition was not followed in the reporting of cases. Discussion: This study provides evidence of endemicity of typhoid fever in Buguias, Benguet, Philippines. However, from January to October 2022, cases were overreported by the surveillance system. Medical record reviews showed that most reported suspected cases did not meet case definition criteria. This finding emphasizes the need to improve typhoid guidelines with regards to diagnosis using rapid diagnostic tests and to investigate the cost-effectiveness of making confirmatory laboratory tests for typhoid available in the Philippines.

Typhoid conjugate vaccine perceptions and coverage among children and adults: Findings from a post-campaign coverage survey - Harare, Zimbabwe, 2019.

BACKGROUND: In 2019, following a large outbreak of typhoid fever, the Zimbabwe Ministry of Health and Child Care conducted a typhoid conjugate vaccine (TCV) vaccination campaign in nine high-risk suburbs of Harare. We aimed to evaluate TCV vaccination coverage, vaccine perceptions, and adverse events reported after vaccination. METHODS: We conducted a two-stage cluster survey to estimate vaccination coverage in the campaign target areas among children aged 6 months-15 years and to classify coverage as either adequate (≥75 % coverage) or inadequate (<75 % coverage) among adults aged 16-45 years in one suburb. Questionnaires assessed socio-demographic factors, TCV vaccination history, reasons for receiving or not receiving TCV, adverse events following immunization, and knowledge and attitudes regarding typhoid and TCV. RESULTS: A total of 1,917 children from 951 households and 298 adults from 135 households enrolled in the survey. Weighted TCV coverage among all children aged 6 months-15 years was 85.3 % (95 % CI: 82.1 %-88.0 %); coverage was 74.8 % (95 % CI: 69.4 %-79.5 %) among children aged 6 months-4 years and 89.3 % (95 % CI: 86.2 %-91.7 %) among children aged 5-15 years. Among adults, TCV coverage was classified as inadequate with a 95 % confidence interval of 55.0 %-73.1 %. Among vaccinated persons, the most reported reason for receiving TCV (96 % across all age groups) was protection from typhoid fever; the most common reasons for non-vaccination were not being in Harare during the vaccination campaign and not being aware of the campaign. Adverse events were infrequently reported in all age groups (10 %) and no serious events were reported. CONCLUSIONS: The 2019 TCV campaign achieved high coverage among school-aged children (5-15 years). Strategies to increase vaccination coverage should be explored for younger children as part of Zimbabwe's integration of TCV into the routine immunization program, and for adults during future post-outbreak campaigns.

Mobile genetic elements define the non-random structure of the Salmonella enterica serovar Typhi pangenome.

Bacterial relatedness measured using select chromosomal loci forms the basis of public health genomic surveillance. While approximating vertical evolution through this approach has proven exceptionally valuable for understanding pathogen dynamics, it excludes a fundamental dimension of bacterial evolution-horizontal gene transfer. Incorporating the accessory genome is the logical remediation and has recently shown promise in expanding epidemiological resolution for enteric pathogens. Employing k-mer-based Jaccard index analysis, and a novel genome length distance metric, we computed pangenome (i.e., core and accessory) relatedness for the globally important pathogen Salmonella enterica serotype Typhi (Typhi), and graphically express both vertical (homology-by-descent) and horizontal (homology-by-admixture) evolutionary relationships in a reticulate network of over 2,200 U.S. Typhi genomes. This analysis revealed non-random structure in the Typhi pangenome that is driven predominantly by the gain and loss of mobile genetic elements, confirming and expanding upon known epidemiological patterns, revealing novel plasmid dynamics, and identifying avenues for further genomic epidemiological exploration. With an eye to public health application, this work adds important biological context to the rapidly improving ways of analyzing bacterial genetic data and demonstrates the value of the accessory genome to infer pathogen epidemiology and evolution.IMPORTANCEGiven bacterial evolution occurs in both vertical and horizontal dimensions, inclusion of both core and accessory genetic material (i.e., the pangenome) is a logical step toward a more thorough understanding of pathogen dynamics. With an eye to public, and indeed, global health relevance, we couple contemporary tools for genomic analysis with decades of research on mobile genetic elements to demonstrate the value of the pangenome, known and unknown, annotated, and hypothetical, for stratification of Salmonella enterica serovar Typhi (Typhi) populations. We confirm and expand upon what is known about Typhi epidemiology, plasmids, and antimicrobial resistance dynamics, and offer new avenues of exploration to further deduce Typhi ecology and evolution, and ultimately to reduce the incidence of human disease.

Modelling Salmonella Typhi in high-density urban Blantyre neighbourhood, Malawi, using point pattern methods.

Salmonella Typhi is a human-restricted pathogen that is transmitted by the faecal-oral route and causative organism of typhoid fever. Using health facility data from 2016 to 2020, this study focuses on modelling the spatial variation in typhoid risk in Ndirande township in Blantyre. To pursue this objective, we developed a marked inhomogeneous Poisson process model that allows us to incorporate both individual-level and environmental risk factors. The results from our analysis indicate that typhoid cases are spatially clustered, with the incidence decreasing by 54% for a unit increase in the water, sanitation, and hygiene (WASH) score. Typhoid intensity was also higher in children aged below 18 years than in adults. However, our results did not show evidence of a strong temporal variation in typhoid incidence. We also discuss the inferential benefits of using point pattern models to characterise the spatial variation in typhoid risk and outline possible extensions of the proposed modelling framework.

Clinical characteristics of enteric fever and performance of TUBEX TF IgM test in Indonesian hospitals.

BACKGROUND: Accurate diagnosis of enteric fever is challenging, particularly in low- and middle-income countries, due to the overlap of clinical and laboratory features with other pathogens. To better understand the difficulties in enteric fever diagnosis, we evaluated the characteristics of patients clinically diagnosed with enteric fever and the real-world performance of TUBEX TF, one of the most used tests in Indonesia. METHODOLOGY/PRINCIPAL FINDINGS: Patients were recruited through the AFIRE (Etiology of Acute Febrile Illness Requiring Hospitalization) study at eight Indonesian hospitals. Blood culture was performed for all patients, and TUBEX TF was performed for suspected enteric cases. Salmonella PCR and ELISA tests were performed at a reference lab. Sensitivity and specificity of TUBEX TF and IgM and IgG anti-S. Typhi ELISA were determined. Of 301 patients clinically diagnosed with enteric fever, 50 (16.6%) were confirmed by blood culture and/or PCR. Confirmed cases were mostly school-aged children presenting with fever, anorexia, dizziness and/or abdominal pain with normal leukocyte count or leukopenia. TUBEX TF demonstrated a sensitivity of 97.6% to 70.7% and specificity of 38.3% to 67.2% at cutoffs of 4 and 6, respectively. Acute IgG demonstrated the best sensitivity and specificity, at 90.7% and 82.7%, respectively, and the best ROC characteristics. CONCLUSIONS/SIGNIFICANCE: A substantial proportion of enteric fever was misdiagnosed at all study hospitals, likely due to the overlap of clinical characteristics and lab parameters with those of other common pathogens. The TUBEX TF rapid serological assay demonstrated suboptimal performance in our setting and tended to over-diagnose enteric fever. The role of IgG from acute specimens for identification of enteric fever cases merits additional consideration.

Pathogen diversity and antimicrobial resistance transmission of Salmonella enterica serovars Typhi and Paratyphi A in Bangladesh, Nepal, and Malawi: a genomic epidemiological study.

BACKGROUND: Enteric fever is a serious public health concern. The causative agents, Salmonella enterica serovars Typhi and Paratyphi A, frequently have antimicrobial resistance (AMR), leading to limited treatment options and poorer clinical outcomes. We investigated the genomic epidemiology, resistance mechanisms, and transmission dynamics of these pathogens at three urban sites in Africa and Asia. METHODS: S Typhi and S Paratyphi A bacteria isolated from blood cultures of febrile children and adults at study sites in Dhaka (Bangladesh), Kathmandu (Nepal), and Blantyre (Malawi) during STRATAA surveillance were sequenced. Isolates were charactered in terms of their serotypes, genotypes (according to GenoTyphi and Paratype), molecular determinants of AMR, and population structure. We used phylogenomic analyses incorporating globally representative genomic data from previously published surveillance studies and ancestral state reconstruction to differentiate locally circulating from imported pathogen AMR variants. Clusters of sequences without any single-nucleotide variants in their core genome were identified and used to explore spatiotemporal patterns and transmission dynamics. FINDINGS: We sequenced 731 genomes from isolates obtained during surveillance across the three sites between Oct 1, 2016, and Aug 31, 2019 (24 months in Dhaka and Kathmandu and 34 months in Blantyre). S Paratyphi A was present in Dhaka and Kathmandu but not Blantyre. S Typhi genotype 4.3.1 (H58) was common in all sites, but with different dominant variants (4.3.1.1.EA1 in Blantyre, 4.3.1.1 in Dhaka, and 4.3.1.2 in Kathmandu). Multidrug resistance (ie, resistance to chloramphenicol, co-trimoxazole, and ampicillin) was common in Blantyre (138 [98%] of 141 cases) and Dhaka (143 [32%] of 452), but absent from Kathmandu. Quinolone-resistance mutations were common in Dhaka (451 [>99%] of 452) and Kathmandu (123 [89%] of 138), but not in Blantyre (three [2%] of 141). Azithromycin-resistance mutations in acrB were rare, appearing only in Dhaka (five [1%] of 452). Phylogenetic analyses showed that most cases derived from pre-existing, locally established pathogen variants; 702 (98%) of 713 drug-resistant infections resulted from local circulation of AMR variants, not imported variants or recent de novo emergence; and pathogen variants circulated across age groups. 479 (66%) of 731 cases clustered with others that were indistinguishable by point mutations; individual clusters included multiple age groups and persisted for up to 2·3 years, and AMR determinants were invariant within clusters. INTERPRETATION: Enteric fever was associated with locally established pathogen variants that circulate across age groups. AMR infections resulted from local transmission of resistant strains. These results form a baseline against which to monitor the impacts of control measures. FUNDING: Wellcome Trust, Bill & Melinda Gates Foundation, EU Horizon 2020, and UK National Institute for Health and Care Research.

Antibiotic resistance trends in high-risk lineages of Salmonella enterica serovar Typhi: A study spanning pre to post COVID-19 pandemic.

OBJECTIVES: The aim of this study was to understand the status of extensively drug-resistance (XDR) genotype in Salmonella enterica serotype Typhi (S. Typhi) recovered during the pre to post COVID-19 pandemic period using Multiplex PCR. METHODS: A longitudinal descriptive study was carried out during five years. Antibiotic susceptibility testing was performed according to the Clinical Laboratory Standards Institute antimicrobial susceptibility testing guidelines. The identification of S. Typhi, the detection of their high-risk lineages and XDR genotype was done using single nucleotide polymorphism-based multiplex PCR. RESULTS: A total of four hundred nine (n = 409) S. Typhi isolates were recovered during pre to post COVID-19 pandemic period. Among them, 30.81% belonged to the pre COVID-19 period while 69.19% to the post COVID-19 period. Different trends in antibiotic resistance in S. Typhi isolates with high prevalence of XDR-S. Typhi were observed. However, there was comparatively different frequency of their occurrence among the S. Typhi isolates recovered during pre to post COVID-19 pandemic period. Multiplex PCR showed that the majority of S. Typhi isolates were the H58 haplotype or genotype 4.3.1 which contained XDR genotype. CONCLUSIONS: The increasing episodes of XDR-S. Typhi causing typhoid fever in endemic areas is alarming. The antibiotic resistance in food and water borne pathogens greatly contribute to the dissemination of the antimicrobial resistance in pathogenic bacteria, which has now been considered as a global concern.

Extensively Drug-Resistant Salmonella Typhi: A National Disaster.

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A portable label-free electrochemical DNA biosensor for rapid detection of Salmonella Typhi.

A highly accurate, rapid, portable, and robust platform for detecting Salmonella enterica serovar Typhi (S. Typhi) is crucial for early-stage diagnosis of typhoid to avert and control the outbreaks of this pathogen, which threaten global public health. This study presents a proof-of-concept for our developed label-free electrochemical DNA biosensor system for S. Typhi detection, which employs a printed circuit board gold electrode (PCBGE), integrated with a portable potentiostat reader. Initially, the functionalized DNA biosensor and target detection were characterized using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) methods using a benchtop potentiostat. Interestingly, the newly developed DNA biosensor can identify target single-stranded DNA concentrations ranging from 10 nM to 20 µM, achieving a detection limit of 7.6 nM within a brief 5 minute timeframe. Under optimal detection conditions, the DNA biosensor exhibits remarkable selectivity, capable of distinguishing a single mismatch base pair from the target single-stranded DNA sequence. We then evaluated the feasibility of the developed DNA biosensor system as a diagnostic tool by detecting S. Typhi in 50 clinical samples using a portable potentiostat reader based on the DPV technique. Remarkably, the developed biosensor can distinctly distinguish between positive and negative samples, indicating that the miniaturised DNA biosensor system is practical for detecting S. Typhi in real biological samples. The developed DNA biosensor device in this work proves to be a promising point-of-care (POC) device for Salmonella detection due to its swift detection time, uncomplicated design, and streamlined workflow detection system.