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: Salmonella Typhi is a human-restricted serovar.
Geographical distribution: Serovar Typhi is globally distributed; however, the prevalence of this serovar varies considerable. Crump et al. concluded that typhoid fever incidence is highest in south-central and southeast Asia, with over 100 cases per 100,000 people annually. Medium incidence rates (10–100 cases per 100,000 per year) are found in other parts of Asia, Africa, Latin America, the Caribbean, and Oceania (excluding Australia and New Zealand). In contrast, Europe, North America, and other developed regions report low typhoid fever rates, with fewer than 10 cases per 100,000 people each year.
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 | 72 | |
2010 | US: multistate | 9 | |
2002 | Nepal | 5963 | |
2000 | US: NY | 7 | |
1998-1999 | US: FL | At least 16 | |
1998 | France | 27 | |
1983 | UK | 32 | |
1937 | UK | 341 | |
1915 | US: NY | 25 | |
1907 | US: NY | 53 |
1 The outbreak was associated with travel 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.
Relevant links: