Salmonella Typhi

Background: Salmonella enterica subsp. enterica serovar Typhi is a serovar of the O:9 (D1) serogroup. S. Typhi causes typhoid fever, a life-threatening disease that is characterized by sustained fever as high as 103° to 104° F (39° to 40° C). In developed countries, this serovar is considered rare; however, in developing countries, it is among the top ten Salmonella serovars that caused disease in humans. S. Typhi kills approx. 600.000 people annually. A number of projects have sequenced the genome of strains of S. Typhi; these studies have concluded that S. Typhi is a highly clonal serovar that emerged approx. 30,000-50,000 years ago. In addition, studies have found that horizontal gene transfer plays an important role in the evolution S. Typhi, this included the acquisition of plasmids encoding multiple antibiotic resistant genes in multidrug resistant strains.

Relevant genetic characteristics: Plasmids and prophages have been identified in S. Typhi. For example, a resistant plasmid of 218 kb and seven prophages were detected in S. Typhi CT18. Up to 15 Salmonella pathogenicity islands (SPIs) have been detected in S. Typhi, these include SPI-1 to 7, 9, 11 to 13, and 15 to 18. Comparative genomics and phylogenetic analyses have shown that S. Typhi (i) had a monophyletic origin approx. 50,000 years ago (ii) has suffered reductive evolution (approx. 200 genes are functionally inactive), (iii) belongs to clade A, according to den Bakker et al. (2011) classification, and (iv) has 349 gene families unique to this serovar.

Animal reservoir: S. Typhi is a human-restricted serovar.

Geographical distribution: Serovar Typhi is globally distributed; however, the prevalence of this serovar varies considerable. In developed countries (U.S., Canada, Europe), S. Typhi isolations correspond to less than 1% of all Salmonella serovars isolated from humans. In developing countries, S. Typhi isolations correspond to up to. 30% of all Salmonella isolated in some countries in Latin America and Asia.

Human outbreaks: Multiple human outbreaks linked to serovar Typhi has been reported. Below are some examples.

Year	Location	Associated source	Number of cases
2022	Netherlands	Raw sewage	72
2010	US: multistate	Frozen mamey fruit pulp	9
2002	Nepal	Drinking water	5963
2000	US: NY	Food handler	7
1998-1999	US: FL	Imported frozen fruit	At least 16
1998	France	Chicken rice	27
1983	UK	Salad¹	32
1937	UK	Water	341
1915	US: NY	Typhoid Mary	25
1907	US: NY	Typhoid Mary	53

¹ All patients traveled to Kos, Greece.

Border rejections: There have been no recent border rejections linked to this serovar.

Recalls:

Year	Location	Recalled food	Type
2010	US: multistate	Frozen mamey fruit pulp¹	Fruits and vegetables

¹ This recall was caused by a multistate outbreak described above. Goya Foods, Inc. and Montalvan’s Sales, Inc. issued voluntary recalls of their fruit pulp products.

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Salmonella Typhi