Estimating the Burden of Paratyphoid A in Asia and Africa

Abstract

Despite the increasing availability of typhoid vaccine in many regions, global estimates of mortality attributable to enteric fever appear stable. While both Salmonella enterica serovar Typhi (S. Typhi) and serovar Paratyphi (S. Paratyphi) cause enteric fever, limited data exist estimating the burden of S. Paratyphi, particularly in Asia and Africa.We performed a systematic review of both English and Chinese-language databases to estimate the regional burden of paratyphoid within Africa and Asia. Distinct from previous reviews of the topic, we have presented two separate measures of burden; both incidence and proportion of enteric fever attributable to paratyphoid. Included articles reported laboratory-confirmed Salmonella serovar classification, provided clear methods on sampling strategy, defined the age range of participants, and specified the time period of the study.A total of 64 full-text articles satisfied inclusion criteria and were included in the qualitative synthesis. Paratyphoid A was commonly identified as a cause of enteric fever throughout Asia. The highest incidence estimates in Asia came from China; four studies estimated incidence rates of over 150 cases/100,000 person-years. Paratyphoid A burden estimates from Africa were extremely limited and with the exception of Nigeria, few population or hospital-based studies from Africa reported significant Paratyphoid A burden.While significant gaps exist in the existing population-level estimates of paratyphoid burden in Asia and Africa, available data suggest that paratyphoid A is a significant cause of enteric fever in Asia. The high variability in documented incidence and proportion estimates of paratyphoid suggest considerable geospatial variability in the burden of paratyphoid fever. Additional efforts to monitor enteric fever at the population level will be necessary in order to accurately quantify the public health threat posed by S. Paratyphi A, and to improve the prevention and treatment of enteric fever.

Diagnostics for invasive Salmonella infections: Current challenges and future directions

“…Similarly, enteric fever remains among the leading causes of disability from an infectious disease in the developing world [2]. Recent estimates of typhoidal Salmonella incidence have varied substantially [3–6], and iNTS estimates are sparse [7–9], in large part due to poor access to reliable diagnostics, particularly in low-resource outpatient settings where patients with these illnesses typically present for medical care. Measured by its burden and influence on antibiotic use, invasive Salmonellosis is perhaps the most important infectious disease cluster for which rapid and reliable (>90% sensitivity and specificity) diagnostics do not exist.…”

Salmonella infection: Interplay between the bacteria and host immune system

“…Thus, the vaccine is unlikely to be efficacious in children under 18 months of age, owing to the immaturity of their splenic marginal zones, which are required for T cell independent antibody responses [39]. It should also be noted that the Vi capsular vaccine cannot protect against disease caused by S. Paratyphi A, which is increasing in Asia, as this serovar doesn’t express Vi capsule and so immunity directed against this antigen is rendered ineffective [40,41]. No vaccines currently exist against iNTS.…”

Typhoid Fever as a Challenge for Developing Countries and Elusive Diagnostic Approaches Available for the Enteric Fever

“…Different rates of detection are not only dependent on local epidemiological dynamics but may also relate to the analytical and diagnostic performances of microbiological methods used for diagnosis [89]. Recent estimates of typhoidal Salmonella incidence have varied substantially and NTS estimates are sparse in large part due to poor access to reliable diagnostics, particularly in low resource outpatient settings where patients with these illnesses typically present for medical care [92,93,94,95].…”