Protection conferred by typhoid fever against recurrent typhoid fever in urban Kolkata.

Justin Im,Faisal Ahmmed,Dipika Sur,Mohammad Ali,Florian Marks,Md Taufiqul Islam,Suman Kanungo,Firdausi Qadri,Kathryn E Holt,Shanta Dutta,Sujit K Bhattacharya,Ashraful Islam Khan,Gordon Dougan,Jerome H Kim,K Zaman,Yun Chon,Deok Ryun Kim,John D Clemens

doi:10.1371/journal.pntd.0008530

Abstract

We evaluated the protection conferred by a first documented visit for clinical care of typhoid fever against recurrent typhoid fever prompting a visit. This study takes advantage of multi-year follow-up of a population with endemic typhoid participating in a cluster-randomized control trial of Vi capsular polysaccharide typhoid vaccine in Kolkata, India. A population of 70,566 individuals, of whom 37,673 were vaccinated with one dose of either Vi vaccine or a control (Hepatitis A) vaccine, were observed for four years. Surveillance detected 315 first typhoid visits, among whom 4 developed subsequent typhoid, 3 due to reinfection, defined using genomic criteria and corresponding to -124% (95% CI: -599, 28) protection by the initial illness. Point estimates of protection conferred by an initial illness were negative or negligible in both vaccinated and non-vaccinated subjects, though confidence intervals around the point estimates were wide. These data provide little support for a protective immunizing effect of clinically treated typhoid illness, though modest levels of protection cannot be excluded.

Highlights

Typhoid fever is a systemic bacterial infection caused by Salmonella enterica serovar Typhi
Recurrent episodes of typhoid fever can occur in individuals, those living in typhoid endemic regions
In theory, offer a degree of protection against future typhoid, this protection has only been assessed in a limited number of studies, none of which were conducted recently nor in the context of a carefully controlled clinical trial

Summary

Introduction

Typhoid fever is a systemic bacterial infection caused by Salmonella enterica serovar Typhi Typhi) and is responsible for significant levels of morbidity and mortality in low- and middleincome countries. Global burden of disease studies have estimated that 14.3 million cases of typhoid fever occur annually [1], and case-fatality rates have dropped to

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Conclusion