TYPHOID FEVER IN THE 21ST CENTURY: EPIDEMIOLOGY, ANTIMICROBIAL RESISTANCE, DIAGNOSTICS, VACCINATION STRATEGIES, AND FUTURE THERAPEUTIC APPROACHES

Background: Typhoid fever, caused by Salmonella enterica serovar Typhi (S. Typhi), remains a significant public health challenge in low- and middle-income countries (LMICs), particularly across South Asia, sub-Saharan Africa, and Southeast Asia. Despite advances in sanitation and healthcare infrastructure, the disease continues to exact a heavy toll on vulnerable populations, with an estimated 11–21 million cases occurring annually and approximately 128,000–161,000 deaths reported each year. Children under five years of age bear a disproportionate burden, and the emergence of drug-resistant strains has complicated treatment protocols substantially. Current Global Burden: The World Health Organization (WHO) identifies typhoid fever as a priority disease requiring urgent attention in the context of global antimicrobial resistance (AMR). Recent large-scale epidemiological studies, including the Global Enteric Multicenter Study (GEMS) and the Surveillance for Enteric Fever in Asia Project (SEAP), have revised earlier incidence estimates upward, highlighting the inadequacy of passive surveillance systems. Urban slums, peri-urban settings with inadequate sanitation infrastructure, and regions experiencing political instability or humanitarian crises contribute disproportionately to the global disease burden. Emerging Challenges: The therapeutic landscape for typhoid fever has been fundamentally altered by the emergence and rapid global dissemination of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains of S. Typhi. The XDR strain, first described from Hyderabad, Pakistan in 2016, carries resistance to first-line antibiotics (chloramphenicol, ampicillin, trimethoprim-sulfamethoxazole), fluoroquinolones, and third-generation cephalosporins, leaving azithromycin and carbapenems as the only reliable oral and injectable treatment options, respectively. This genomic evolution represents one of the most significant public health emergencies in enteric fever management. Diagnostic Limitations: Accurate and timely diagnosis of typhoid fever remains constrained by the poor sensitivity of blood culture in field settings, the unreliability of serological tests such as the Widal test in endemic regions, and the lack of affordable point-of-care molecular diagnostics. Emerging technologies including CRISPR-Cas12-based biosensors, loop-mediated isothermal amplification (LAMP), and artificial intelligence-assisted diagnostic platforms offer promising avenues but remain largely unvalidated at scale in resource-limited settings. Scope of the Review: This comprehensive review synthesizes evidence from 150 peer-reviewed publications, WHO reports, and epidemiological databases published over the past fifteen years. It examines the current global epidemiology of typhoid fever, elucidates the molecular mechanisms underlying antimicrobial resistance, evaluates the performance characteristics of conventional and emerging diagnostic modalities, assesses the safety and efficacy profiles of currently available vaccines including typhoid conjugate vaccines (TCVs), and explores novel therapeutic strategies including phage therapy, nanomedicine-based drug delivery, and host-directed therapeutic interventions. Major Findings: Our review identifies several critical findings. First, the global incidence of typhoid fever remains substantially underestimated due to inadequate surveillance infrastructure. Second, XDR typhoid has evolved through the acquisition of resistance determinants on a single IncY plasmid and continues to spread internationally through travel and trade networks. Third, typhoid conjugate vaccines demonstrate 79–82% efficacy in clinical trials and represent a major advancement over unconjugated polysaccharide vaccines, particularly in children under two years of age. Fourth, WASH (Water, Sanitation, and Hygiene) interventions remain the most cost-effective long-term control measure but require sustained political commitment and financing. Fifth, whole-genome sequencing (WGS) of S. Typhi isolates has revolutionized our understanding of the pathogen's global phylogeography and resistance evolution. Research Gaps and Future Perspectives: Significant knowledge gaps persist regarding the immunological correlates of protection following vaccination, the role of environmental reservoirs in sustaining transmission cycles, and the long-term durability of TCV-induced immunity. Future research must prioritize the development of rapid, affordable, field-deployable diagnostics, next-generation vaccine candidates with broader serological coverage, and novel antimicrobial agents with activity against XDR strains. International collaboration through platforms such as the Global Typhoid Alliance and the Coalition Against Typhoid (CaT) is imperative to accelerate progress across these domains. Conclusions: Effective control of typhoid fever in the 21st century demands an integrated, multisectoral approach combining vaccination, improved water and sanitation infrastructure, enhanced antimicrobial stewardship, and strengthened surveillance systems. The global scientific community must intensify efforts to translate genomic and immunological insights into clinically actionable tools that can reach the populations most burdened by this preventable disease.