Typhoid fever is a severe infection causing a sustained high fever. It is caused by the bacteria Salmonella typhi, which is similar to the bacteria spread by chicken and eggs that results in "Salmonella poisoning" or food poisoning. S. typhi bacteria, however, do not multiply directly in food, as do the Salmonella responsible for food poisoning, nor does it have vomiting and diarrhea as the most prominent symptoms. Instead, persistently high fever is the hallmark of infection with Salmonella typhi.

S. typhi bacteria are passed into the stool and urine of infected patients, and may continue to be present in the stool of asymptomatic carriers (individuals who have recovered from the symptoms of the disease, but continue to carry the bacteria). This carrier state occurs in about 3% of all individuals recovered from typhoid fever.

The disease is passed between humans, then, through poor hygiene, such as...