Objectives: In Santiago, Chile, where typhoid had been hyperendemic (1977-1991), we investigated whether residual chronic carriers could be detected among household contacts of non-travel-related typhoid cases occurring 2017-2019.
Methods: Culture-confirmed cases were classified as "autochthonous" (domestically-acquired) versus "travel/immigration-related". Household contacts of cases had stool cultures and serum Vi antibody measurements to detect chronic Salmonella Typhi carriers. Whole genome sequences of acute cases and their epidemiologically-linked chronic carrier isolates were compared.
Results: Five of 16 autochthonous typhoid cases (31.3%) were linked to four chronic carriers in case households; two cases (onsets 23 months apart) were linked to the same carrier. Carriers were women aged 69-79 years with gallbladder dysfunction and Typhi fecal excretion; three had highly elevated serum anti-Vi titers. Genomic analyses revealed close identity (≤11 core genome SNP [Single Nucleotide Polymorphism] differences) between case and epidemiologically-linked carrier isolates; all were genotypes prevalent in 1980s Santiago. A cluster of four additional autochthonous cases un-linked to a carrier was identified based on genomic identity (0-1 SNPs). Travel/immigration isolate genotypes were typical for the countries of travel/immigration.
Conclusions: Although autochthonous typhoid cases in Santiago are currently rare, 5/16 such cases (31.3%) were linked to elderly chronic carriers identified among household contacts of cases.
Keywords: chronic typhoid carriers; short-cycle typhoid transmission; transmission of typhoid; typhoid elimination; typhoid fever.
© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America.