Rethinking Typhoid Fever Vaccines: Implications for Travelers and People Living in Highly Endemic Areas

Abstract

Enteric (typhoid or paratyphoid) fever is a systemic infection caused by Salmonella enterica , including S enterica serotype Typhi ( S typhi ) and serotypes Paratyphi A, B, and C ( S paratyphi ). Humans are the only host for these pathogens, which are transmitted by fecal contamination of food and water. Salmonella typhi caused an estimated 22 million illnesses and 200,000 deaths, and S paratyphi caused 5.4 million illnesses worldwide during the year 2000. 1 The actual global burden of enteric fever is difficult to determine because many cases are unrecognized, particularly in young children who may have a nonspecific illness, 2–4 and it is not a notifiable disease in endemic countries. In addition, there are no specific clinical diagnostic criteria, and the laboratory techniques for diagnosis lack sensitivity and specificity. 5 According to the recently estimated global incidence, the highest concentration of typhoid fever is in Asia, especially in the Indian subcontinent (Table 1). 1 Southern Africa and Latin America also have a high disease burden (Table 1). View this table: Table 1 Crude typhoid fever incidence rates by region, 2000 Previously, S paratyphi was thought to have caused 10% of cases of enteric fever and a milder form of disease than S typhi. 6,7 However, recent reports suggest that these two pathogens cause similar diseases 8–10 and that there has been a disproportionate increase in the incidence of enteric fever caused by S paratyphi , with up to 50% of enteric fever cases caused by S paratyphi in some highly endemic areas of the world. 9,11–15 Enteric fever also affects short‐term and long‐term travelers bound to highly endemic areas. 16 Among the travel‐related cases, most occur in foreign‐born residents who visited friends or family in their country of origin. 17 Travel to the Indian subcontinent is associated with the highest risk of contracting enteric fever. 18–20 … Corresponding Author: Carlos Franco‐Paredes, MD, MPH, Department of Medicine, Division of Infectious Diseases, Emory University School of Medicine, 550 Peachtree Street, MOT, 7th Floor, TravelWell, Atlanta, GA 30308, USA. E‐mail: cfranco{at}sph.emory.edu