• Salmonella enterica typhi is the bacteria that causes typhoid fever. The bacteria, which is now simply called Salmonella typhi, or S. typhi, lives only in humans, according to the U.S. Centers for Disease Control and Prevention, and can be spread through contaminated water, food and beverages. Typhoid fever is rare in the United States, with only about 400 cases reported annually, according to the CDC. Most cases in the U.S. originated in foreign countries, especially developing nations, where 21.5 million people contract the illness each year.
  
  

Fever

• A common early sign of an S. typhi infection is a fever. People with typhoid fever can develop a fever as high as 103 degrees or 104 degrees Fahrenheit and may sustain the fever for a period of several days.
  
  

Gastrointestinal Symptoms

• An early symptom of typhoid fever is abdominal pain or discomfort. People also often experience diarrhea or bloody stools. As the infection progresses without treatment, diarrhea typically worsens, although in some cases constipation can develop.
  
  

Neurological Symptoms

• If an S. typhi infection is allowed to progress without treatment, neurological signs of the infection may be noticed. For example, people can be agitated or have difficulty paying attention or concentrating. Mood swings are common, and people can be mentally confused or suffer hallucinations. In advanced stages, when the infection reaches what is called the typhoid state, people can be delirious and may simply lay motionless.
  
  

Other Signs and Symptoms

• Other signs and symptoms commonly associated with typhoid fever include extreme fatigue, a sore throat, weight loss, weakness and nosebleeds. Some people also develop a rash consisting of small, flat, reddish or pinkish spots.
  Many of the signs and symptoms of an S. Typhi infection are similar to those of other infectious diseases. The only way to definitively diagnose typhoid fever is through a culture of a person's blood, stool or body fluid.