Vaccine-Preventable Diseases

Typhoid

Typhoid fever is caused by Salmonella typhi, which differs from most other Salmonella species in that it infects only humans and frequently causes severe systemic illness. The organism is generally transmitted through food contaminated with the feces or urine of people with the disease or those who are S. typhi carriers. The fatality rate is approximately 16% for untreated cases and 1% for those given appropriate antibiotic therapy. Between 2% and 5% of typhoid cases become chronic carriers, sometimes shedding bacteria in stool for years. The risk of severe illness is increased in people with depressed immunity (e.g., due to HIV) or decreased gastric acid levels.

Epidemiology

In endemic areas (such as Africa [with the exception of South Africa], Asia [except for Singapore and Japan], the Middle East [except Israel and Kuwait], Central and South America, the Dominican Republic and Haiti in the Caribbean) typhoid fever has long been considered a disease that has its greatest impact in individuals 5 to 19 years of age. Age-specific incidence rates vary from one country to another, however, and significant illness and numbers of deaths have been reported in children < 5 years of age in some settings. Several factors may contribute to an apparently lower risk in very young children, including age-specific changes in the immune response, atypical or milder disease in this population and under-reporting. Whatever the cause(s), the observation is important in light of our incomplete knowledge of vaccine immunogenicity and efficacy in this age group.

The incidence of typhoid fever is very low in the industrialized world. An average of 70 cases have been reported annually in Canada over the past 5 years. The low incidence rate in industrialized countries is attributable to overall good living conditions, in particular the high quality of drinking water and sewage treatment. The rates were achieved without vaccines, and vaccination has no ongoing role in disease control.

The greatest risk of typhoid infection for Canadians occurs while they are travelling in countries where sanitation is likely to be poor. However, not all travellers in these countries are at markedly increased risk. Indeed, the risk of suffering from typhoid fever in many settings in developing countries is minimal (e.g., business-class hotels, conference centres and resort hotels). The greatest risk appears to be associated with exposures to food and water in uncontrolled settings (e.g., market stalls, street vendors, home restaurants and family settings). Even relatively short visits with friends and family can put Canadian travellers (the so-called "visiting friends and relatives" or VFR group) at substantial risk of typhoid in some areas.

Regardless of the setting, typhoid immunization is not a substitute for careful selection and handling of food and water. The available vaccines provide only 50% to 55% protection and do not prevent disease in those who ingest a large number of organisms. However, immunization may reasonably be expected to reduce the risk of typhoid fever among otherwise healthy travellers in areas where this disease is either endemic or epidemic.

Source: Canadian Immunization Guide, 7^th edition, 2006

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Links to more information

Guidelines and Recommendations

• For information about Typhoid vaccine, see the Canadian Immunization Guide, 7^th edition 2006

Travel Medicine Program

• Immunizations Recommended for Travel Outside of Canada