Typhoid fever is caused by the bacterium Salmonella typhi. It is transmitted through contaminated food or water. S. typhi bacteria infect the intestines and sometimes spread to the bloodstream, causing systemic infection. Symptoms include sustained fever, headache, vomiting, diarrhea, and abdominal pain. Laboratory diagnosis involves culturing bacteria from blood or urine samples or detecting antibodies in serum using tests like the Widal test. Effective treatment is with antibiotics such as ciprofloxacin or ceftriaxone. Rehydration is also important, and in severe cases surgery may be needed if the bowel is perforated.