Typhoi fever, also known as enteric fever, bilious fever or Yellow Jack, is an illness caused by the bacterium Salmonella enterica serovar Typhi. Common worldwide, it is transmitted by the ingestion of food or water contaminated with faeces from an infected person. The bacteria then multiply in the blood stream of the infected person and are absorbed into the digestive tract and eliminated with the waste. The organism is a Gram-negative short bacillus that is motile due to its peritrichous flagella. The bacteria grows best at 37°C (human body temperature).