Comparative Analysis of Commercially Available Typhoid Point-of-Care Tests: Results of a Prospective and Hybrid Retrospective Multicenter Diagnostic Accuracy Study in Kenya and Pakistan

Typhoid fever

Typhoid fever is an invasive bacterial disease associated with bloodstream infection that causes a high burden of disease in Africa and Asia. Typhoid primarily affects individuals ranging from infants through to young adults. The causative organism, Salmonella enterica subsp. enterica serovar Typhi is transmitted via the faecal-oral route, crossing the intestinal epithelium and disseminating to systemic and intracellular sites, causing an undifferentiated febrile illness. Blood culture remains the practical reference standard for diagnosis of typhoid fever, where culture testing is available, but novel diagnostic modalities are an important priority under investigation. Since 2017, remarkable progress has been made in defining the global burden of both typhoid fever and antimicrobial resistance; in understanding disease pathogenesis and immunological protection through the use of controlled human infection; and in advancing effective vaccination programmes through strategic multipartner collaboration and targeted clinical trials in multiple high-incidence priority settings. This Primer thus offers a timely update of progress and perspective on future priorities for the global scientific community.

Use of onsite typhoid IgG/IgM combo test as rapid diagnostic test for typhoid fever

Background

The incidence of typhoid fever is increasing in Egypt. The Widal test is the evaluation most widely used in Egypt for diagnosis, but it has many drawbacks; therefore, new diagnostic tools are needed. Our aim was to evaluate the diagnostic accuracy of the onsite typhoid IgG/IgM combo rapid test in diagnosing typhoid fever.

Method

Blood specimens were collected from 90 patients (of all ages) who presented with fever of more than 4 days’ duration. The OnSite Combo test and the Widal test were performed for all patients.

Results

The OnSite Combo test results were positive in approximately 24% of all patients; the Widal test results were positive in 18.9%; and typhoid was diagnosed through blood culture in 32.2%. The OnSite Combo test had 72.4% sensitivity, 98.4% specificity, a positive predictive value of 95.5%, and a negative predictive value of 88.2%. In contrast, the Widal test had 51.7% sensitivity, 69.7% specificity, a positive predictive value of 88.2%, and a negative predictive value of 80.8%.

Conclusions

The onsite combo test was more efficacious than the Widal test in diagnosing typhoid fever.

Progress in the Typhoid Conjugate Vaccine Program Rollout Supported by Gavi During the COVID-19 Pandemic and the Path Forward

Gavi supports countries to introduce typhoid conjugate vaccine (TCV) with catch-up campaigns. Available TCVs are highly efficacious, equity-focused, and critical to curbing the expansion of antimicrobial resistance. Four Gavi-supported countries have introduced TCVs since 2018. In the wake of the COVID-19 emergency, momentum is building to scale up TCV introduction worldwide, supported by global partners and Gavi's funding for improved typhoid diagnostics.

Diagnostics for Typhoid Fever: Current Perspectives and Future Outlooks for Product Development and Access

Typhoid is an enteric disease caused by Salmonella Typhi. Like many febrile illnesses, typhoid presents with nonspecific symptoms. In routine healthcare settings in low- and middle-income countries, typhoid fever is suspected and treated empirically. Though many diagnostic tests are available for typhoid diagnosis, there are currently no diagnostic tests that meet ideal requirements for sensitivity, specificity, speed, and cost-effectiveness. With introduction of typhoid conjugate vaccine, it is essential to explore the current and future typhoid approach in the context of use case and access to ensure their utilization for disease control.