Bacteria of the species Salmonella enterica are gram-negative, flagellated bacteria that are non-spore forming and facultatively anaerobic.

A total of around 2,500 Salmonella enterica serovars are currently known. Over 500 serovars have been shown to be pathogenic to humans, the two most common Salmonella serovars are S. enterica Serovar Enteritidis and S. Enterica Serovar Typhimurium (non-typhoidal).

Non-typhoidal salmonella usually cause gastroenterides ("salmonellosis") in humans. Salmonellosis in humans is widespread worldwide and manifests itself as sudden onset of diarrhea, headache and stomach ache, malaise and sometimes vomiting. Mild fever is common. In rare cases, a septic course can follow. Salmonella are highly adapted for reproduction in humans as well as in animals (mammals, reptiles, birds, insects). Farm animals and animal foods produced from them (e.g. eggs, meat) are at the top of the possible causes of infection. However, transmission from person to person is also possible, especially in the context of nosocomial infections or under poor hygienic conditions. In Germany, a total of 16,318 Salmonella diseases were reported to the RKI in accordance with the IfSG in 2017. S. enterica Serovar Choleraesuis is one of the non-typhoidal salmonellae. Due to the expression of certain virulence factors, this bacterium is more invasive (penetration of the epithelial cells in the intestinal tract) than, for example, S. Typhimurium and frequently causes bacteremia. Typhoidal salmonella: S. enterica serovar Typhi and S. enterica serovar paratyphi A, B or C cause systemic infections with intestinal involvement. They are exclusively human pathogenic.

The worldwide annual incidence of typhus abdominalis is estimated at approximately 22 million illnesses and 200,000 deaths. In Germany, a total of 86 typhus cases were reported to the RKI in 2017. With regard to paratyphoid fever, it is estimated that there are 5.5 million cases. In Germany, a total of 52 cases of paratyphoid fever were reported to the RKI in 2017. The clinical course of paratyphoid fever is similar to that of typhoid fever, but it is usually less pronounced. Long-term excretors can excrete pathogens for life.

S. Paratyphi C does not share a common genetic ancestor with the other typhoidal Salmonella, but with the non-typhoidal S. Choleraesuis. This indicates that the typhoidal properties have evolved convergently. The reliable molecular biological differentiation between S. Paratyphi C and S. Choleraesuis therefore requires two genetic target sequences.