Epidemiology

According to estimates from the World Health Organization, there are between 11 and 21 million cases of typhoid and 128,000 to 161,000 typhoid-related deaths annually worldwide.[1]​ The 2017 Global Burden of Disease study reported 14.3 million cases of typhoid and paratyphoid fever in 2017, which was a 44.6% decline from 25.9 million in 1990; there were an estimated 135,900 deaths from typhoid and paratyphoid fever in 2017, which was a 41.0% decline from 230,500 in 1990.[2] The majority of infections (around 70%) are reported from South/South-East Asia, and Sub-Saharan Africa.[2][3][4]

[Figure caption and citation for the preceding image starts]: Incidence rates (per 100 000) of typhoid and paratyphoid fevers, by country, in 2017GBD 2017 Typhoid and Paratyphoid Collaborators. Lancet Infect Dis 2019 Apr;19(4):369-381; used with permission [Citation ends].com.bmj.content.model.Caption@2505321f

The age-standardized incidence rate in south Asia in 2017 was reported as 549 per 100,000, and globally it was 198 per 100,000.[2] The incidence may vary considerably even within a country or city, where it predominantly affects the urban slums.[3] In high-income countries, enteric fever is predominantly a travel-associated disease.

[Figure caption and citation for the preceding image starts]: Incidence of typhoid infection (left) and the percentage of travelers (right)CDC image library [Citation ends].com.bmj.content.model.Caption@c1242bc​ In the US, for example, the annual incidence dropped from 7.5 per 100,000 in 1940 to 0.2 per 100,000 in the 1990s, and the proportion of cases related to foreign travel increased from 33% in 1967 to 72% to 81% in 1996 to 1997.[5][6][7]​ In Israel the change is even more marked, with an annual incidence of 90 per 100,000 in the early 1950s that had dropped to 0.23 per 100,000 in 2003; 57% of these cases were acquired abroad.[8] The overall range of reported annual incidence in industrialized countries ranges from 0.13 to 1.2 cases per 100,000 population, with the overwhelming majority being imported.[5][9][10]​ The risk to travelers appears to vary by geographic region visited.[11][12][13]

Several reports indicate that the Indian subcontinent poses the highest risk for acquiring typhoid infection. While the incidence of typhoid infection among US travelers to Mexico, for example, decreased from 0.19 to 0.13 per 100,000 between 1985 and 1994, the incidence among travelers to the Indian subcontinent increased from 23.4 to 81.2 per 100,000. The overall risk of typhoid infection in travel to the Indian subcontinent is 18 times higher than to any other geographic area.[5]

In Israel, 74% of imported typhoid infection cases were acquired in India and the calculated attack rate was 24 per 100,000 travelers, a figure 100 times higher than those for travelers to Thailand or the Middle East.[14]

Reports from France and Germany also indicate the Indian subcontinent as the main geographic source.[15][16]

A special group with increased risk are those travelers visiting friends and relatives (VFRs): that is, immigrants who return to visit their homeland. In addition to more travel to rural areas, VFR travelers are less likely to have received pre-travel advice, are less likely to keep food and water precautions, and do not receive typhoid vaccine prior to travel.[17]

Death is rare in short-term travelers. A review of Centers for Disease Control and Prevention surveillance data from 1985 to 1994 included 2445 cases of typhoid and found a mortality rate of 0.4%. Deaths occurred exclusively in immigrants rather than short-term travelers.[5] Reports of typhoid infection in hospitalized returning travelers in France, Germany, Israel, and Nepal showed no events of mortality.[14][15][16][18]

An outbreak of typhoid fever caused by a strain of Salmonella typhi resistant to chloramphenicol, ampicillin, trimethoprim/sulfamethoxazole, fluoroquinolones, and ceftriaxone emerged in Pakistan in 2016.[19]​ Extensively drug-resistant (XDR) S typhi has since been documented among travelers, mostly associated with travel to Pakistan.[13][20][21][22]​​​[23]​​​​ In the US, between February 2018 and March 2021, 76 XDR and XDR variant S typhi infections were identified. Of these patients, 67 reported travel to or from Pakistan, but nine had no history of international travel in the 30 days before their sickness and also did not report having close contact with anyone sick.[24]​ No source for infection in the patients who had not traveled has been identified and surveillance for XDR typhoid fever is ongoing.[24]

Enteric fever is a notifiable disease in many countries, with local or national guidelines indicating the reporting requirements.

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