Salmonellosis is caused by a group of gram-negative bacilli and results in mild to severe diarrheal disease. Salmonella is found worldwide. Serotypes Salmonella typhimurium and Salmonella enteritidis are the most common in the United States and are responsible for one million foodborne illnesses annually. The disease is spread through ingestion of contaminated animal products (predominantly turkey, chicken, duck, and eggs) or contact with infected fecal matter. Soft cheese and beef obtained in the United States and Mexico, respectively, have been linked to an emerging strain of multidrug-resistant Salmonella Newport, according to the Centers for Disease Control and Prevention (CDC).

Salmonella enterica serotype typhi and Salmonella enterica serotype paratyphi A, B and C produce the most severe forms of the illness (typhoid and paratyphoid fevers) and are found in most parts of the world except in industrialized regions (United States, Canada, western Europe and Japan). Unlike nontyphoidal Salmonella, typhoid and paratyphoid are strictly human diseases and transmitted via fecal-oral transmission between humans.

The symptoms of nontyphoidal gastroenteritis include low-grade fever, chills, nausea, vomiting, diarrhea, and abdominal cramps. The incubation period is typically 6-72 hours, and illness lasts up to a week. One report of children with this infection noted that 29% had bloody diarrhea, many had fever and vomiting, and some presented with signs of dehydration.

An asymptomatic carrier state may exist for months after recovery from infection. In most cases, antibiotic therapy is not necessary. Rarely (<8% of cases), nontyphoidal gastroenteritis is complicated by bacteremia. For some patients, antibiotic therapy for gastroenteritis might be prescribed if they are felt to be at increased risk for extra-intestinal infection (eg, neonates, the elderly, or immunosuppressed patients). In one small case series, children with bacteremia typically had dysentery and fever on admission. Some had convulsions. Also rare is a reactive arthritis following Salmonella infection. This can be associated with iritis and urethritis.

The incubation period for typhoid or paratyphoid is 6-30 days. The initial symptoms of typhoid and paratyphoid fevers include the acute or gradual onset of abdominal pain and tenderness, fever, chills, sweating, headache, anorexia, weakness, cough, sore throat, dizziness, and myalgias. Fever develops slowly beginning as low grade and rising to temperatures of 102-104°F (39°C-40°C) by the fourth day. This usually progresses to a severe illness with bacteremia and high fever that may last for weeks. Hepatosplenomegaly is common. Some patients will develop a rash of erythematous papules on the trunk (rose spots), and some will suffer altered mental status. Bowel perforation can be seen rarely.

The CDC has classified drug-resistant nontyphoidal Salmonella and drug-resistant Salmonella serotype typhi as serious concerns. They note that 67% of S. typhi are drug-resistant.

The CDC has designated Salmonella as a Category B food or waterborne bioterrorist agent. Salmonella has been used in the past as a bioterrorist agent. In 1984, a religious group, the followers of Bhagwan Shree Rajneesh, intentionally contaminated area salad bars in a small Oregon town.