Typhoid fever is caused by a germ called Salmonella typhi. Parathyroid fever is a milder form of typhoid fever. It is caused by a germ called Salmonella paratyphi. These germs most often infect food and water systems. People get the germs by: Drinking water contaminated by the germs Eating food contaminated with the stool from a person with this illness Having oral or anal sex with someone who is infected with the germs When you have this illness, you may have serious health problems if it is not treated. You may need drugs and care to control the signs of the illness.