Investigation into a community outbreak of Salmonella Typhi in Bengaluru, India

Typhoid Outbreaks, 1989-2018: Implications for Prevention and Control

Typhoid fever remains an important public health problem in low- and middle-income countries, with large outbreaks reported from Africa and Asia. Although the WHO recommends typhoid vaccination for control of confirmed outbreaks, there are limited data on the epidemiologic characteristics of outbreaks to inform vaccine use in outbreak settings. We conducted a literature review for typhoid outbreaks published since 1990. We found 47 publications describing 45,215 cases in outbreaks occurring in 25 countries from 1989 through 2018. Outbreak characteristics varied considerably by WHO region, with median outbreak size ranging from 12 to 1,101 cases, median duration from 23 to 140 days, and median case fatality ratio from 0% to 1%. The largest number of outbreaks occurred in WHO Southeast Asia, 13 (28%), and African regions, 12 (26%). Among 43 outbreaks reporting a mode of disease transmission, 24 (56%) were waterborne, 17 (40%) were foodborne, and two (5%) were by direct contact transmission. Among the 34 outbreaks with antimicrobial resistance data, 11 (32%) reported Typhi non-susceptible to ciprofloxacin, 16 (47%) reported multidrug-resistant (MDR) strains, and one reported extensively drug-resistant strains. Our review showed a longer median duration of outbreaks caused by MDR strains (148 days versus 34 days for susceptible strains), although this difference was not statistically significant. Control strategies focused on water, sanitation, and food safety, with vaccine use described in only six (13%) outbreaks. As typhoid conjugate vaccines become more widely used, their potential role and impact in outbreak control warrant further evaluation.

Molecular analysis of clonally related Salmonella Typhi recovered from epidemiologically unrelated cases of typhoid fever, Brazil

BACKGROUND

The primary method of molecular subtyping for the identification and investigation of outbreaks has been pulsed-field gel electrophoresis (PFGE). In some cases, this technique has not been able to show discrimination between the unrelated strains that can be achieved by whole genome sequencing (WGS).

METHODS

The aim of this study was to determine the strengths and drawbacks of WGS using different analytic approaches compared to traditional typing method, PFGE, for retrospectively typing clusters cases of 28 S. Typhi.

RESULTS

We evaluated three analytical approaches on the WGS data set (Nucleotide Difference (ND), (SNPs) and Whole genome multi locus sequence typing (wgMLST) that identically classified the clusters-related strains into two clusters, cluster A (with strains from 2017), and Cluster B (with strains from 2007).

CONCLUSIONS

In this study WGS based typing, was able to compete with PFGE for differentiation of the clusters of S. Typhi strains.