Health Typhoid & Paratyphoid Fever INFECTIOUS AGENT Salmonella enterica  serotypes Typhi and Paratyphi A, Paratyphi B, and Paratyphi C cause potentially severe and occasionally life-threatening bacteremic illnesses referred to respectively as typhoid and paratyphoid fever, and collectively as enteric fever. Paratyphi B is differentiated into 2 distinct pathotypes on the basis of their ability to ferment tartrate—one is unable to ferment tartrate and is associated with paratyphoid fever (referred to as Paratyphi B), and the other ferments tartrate and is associated with uncomplicated gastroenteritis (referred to as Paratyphi B var. L(+) tartrate+). TRANSMISSION Humans are the only source of these bacteria; no animal or environmental reservoirs have been identified. Typhoid and paratyphoid fever are acquired through consumption of water or food contaminated by feces of an acutely infected or convalescent person or a chronic, asymptomatic carrier. Risk for infection is high in low-