Testing and Diagnostics of Typhoid Causative Salmonella Strains

Enteric fever, commonly known as typhoid fever, is a significant global public health problem, particularly concentrated in South Asia, with India bearing a high burden of the disease. It is estimated that there are 11–21 million cases of enteric fever worldwide each year, resulting in 1,20,000–1,60,000 deaths. Due to the lack of proper diagnosis and heterogeneity of disease, the exact burden of disease is unclear but extrapolation of regional data estimates 586 cases per 100,000 person-years typhoid/paratyphoid incidence in India. The disease can be effectively treated with antibiotics, however escalating global antimicrobial resistance, including the emergence and spread of multidrug-resistant variants of Salmonella enterica serovar Typhi (S. typhi) has worsened the situation. To prevent the further spread of resistant S. Typhi it is imperative to identify antibiotic susceptibility testing for individual patients before commencing antibiotic therapy. Salmonella enterica serovar Paratyphi (S. Paratyphi), also causes enteric fever and affects approximately 3.4 million people annually, resulting in 19.1 thousand deaths in 2 comparisons to 10.9 million cases and116.8 thousand deaths by S. typhi. While the morbidity and mortality of S. typhi make it a greater public health concern, the increasing prevalence of S. paratyphi in certain regions necessitates a next-generation diagnostic test capable of detecting both S. typhi and S. paratyphi. The exciting typhoid diagnostic tests, such as the Widal test, TUBEX, Typhidot and Test-IT (KIT), have shown sub-optimal sensitivity and specificity, leading to challenges in accurately identifying typhoid cases at the point of care (POC). The most widely used RDT is the Widal test which has lower performance (sensitivity range, 57–74%; specificity range, 43–83%) as reported in many studies. The performance of other typhoid RDTs, like TUBEX (average sensitivity of 78% and a specificity of 87%), Typhidot (average sensitivity of 84% and a specificity of 79%), and Test-It (KIT) (average sensitivity of 69% and a specificity of 90%) is also sub-optimal. To have a meaningful impact on the overuse of antibiotics that has contributed to the emergence of resistance in S. typhi and other bacteria, an improved typhoid POC test needs to be used.