Molecular Surveillance Identifies Multiple Transmissions of Typhoid in West Africa

Abstract

BackgroundThe burden of typhoid in sub-Saharan African (SSA) countries has been difficult to estimate, in part, due to suboptimal laboratory diagnostics. However, surveillance blood cultures at two sites in Nigeria have identified typhoid associated with Salmonella enterica serovar Typhi (S. Typhi) as an important cause of bacteremia in children.MethodsA total of 128 S. Typhi isolates from these studies in Nigeria were whole-genome sequenced, and the resulting data was used to place these Nigerian isolates into a worldwide context based on their phylogeny and carriage of molecular determinants of antibiotic resistance.ResultsSeveral distinct S. Typhi genotypes were identified in Nigeria that were related to other clusters of S. Typhi isolates from north, west and central regions of Africa. The rapidly expanding S. Typhi clade 4.3.1 (H58) previously associated with multiple antimicrobial resistances in Asia and in east, central and southern Africa, was not detected in this study. However, antimicrobial resistance was common amongst the Nigerian isolates and was associated with several plasmids, including the IncHI1 plasmid commonly associated with S. Typhi.ConclusionsThese data indicate that typhoid in Nigeria was established through multiple independent introductions into the country, with evidence of regional spread. MDR typhoid appears to be evolving independently of the haplotype H58 found in other typhoid endemic countries. This study highlights an urgent need for routine surveillance to monitor the epidemiology of typhoid and evolution of antimicrobial resistance within the bacterial population as a means to facilitate public health interventions to reduce the substantial morbidity and mortality of typhoid.

The Burden of Typhoid Fever in South Africa: The Potential Impact of Selected Interventions

“…Salmonella Typhi H58 is a highly clonal multidrug-resistant haplotype of Salmonella Typhi that is being reported with increasing frequency from many countries in Africa and Asia. 42 , 43 Continual antimicrobial resistance monitoring has become an essential adjunct to assessing how best to control typhoid fever. 44 Molecular analyses, including PFGE and more recently WGS have confirmed that South Africa remains highly vulnerable to the introduction of multidrug-resistant typhoid fever and potential outbreaks that may result from this, 31 , 32 particularly as ongoing outbreaks of fluoroquinolone-resistant typhoid fever are reported from neighboring countries.…”

Whole Genome Sequence Analysis of Salmonella Typhi Isolated in Thailand before and after the Introduction of a National Immunization Program

“…Typhi population. Importantly, while genomic epidemiology has been applied to study typhoid transmission, antimicrobial resistance evolution and antibiotic treatment failure in various settings [66–68], this study provides an important proof-of-principle demonstration that this approach can also provide useful insights into the impact of typhoid vaccines on circulating bacterial populations. This should motivate the adoption of WGS methods to monitor S .…”

A systematic review of antimicrobial resistance in Salmonella enterica serovar Typhi, the etiological agent of typhoid

“…H58 S . Typhi disease is moving through areas of East and Southern Africa, while, non-H58 haplotypes are implicated in the Western and Northern regions, illustrating the heterogeneous nature of the disease on the continent[ 8 , 9 ].…”