Nontyphoidal Salmonella Infections

Salmonella infection may manifest as

• Gastroenteritis

• Enteric fever

• Bacteremia

• Focal disease

Gastroenteritis usually starts 12 to 48 hours after ingestion of organisms, with nausea and cramping abdominal pain followed by diarrhea, fever, and sometimes vomiting. Usually, the stool is watery but may be a pastelike semisolid. Rarely, mucus or blood is present. The disease is usually mild, lasting 1 to 4 days. Occasionally, a more severe, protracted illness occurs. About 10 to 30% of adults develop reactive arthritis weeks to months after diarrhea stops. Reactive arthritis causes pain and swelling, usually in the hips, knees, and Achilles tendon.

Enteric fever is a term often used interchangeably with typhoid fever. Enteric fever typically refers to a form of typhoid caused by nontyphoidal Salmonella infections caused by S. enterica subspecies; it is characterized by fever, prostration, and septicemia.

Bacteremia is relatively uncommon in patients with gastroenteritis, except in infants (who also can have meningitis) and older adults. However, S. Choleraesuis, S. Typhimurium, and S. Heidelberg, among others, can cause a sustained and frequently lethal bacteremic syndrome lasting ≥ 1 week, with prolonged fever, headache, malaise, and chills but rarely diarrhea. Sustained bacteremia suggests endovascular infection, such endocarditis or infection of an abdominal aortic aneurysm, which can occur as a complication of Salmonella bacteremia. Patients may have recurrent episodes of bacteremia or other invasive infections (eg, infectious arthritis) due to Salmonella. Bacteremia is more likely to occur in patients who are immunologically compromised (eg, those with HIV/AIDS) and in patients with a hemolytic condition (eg, sickle cell anemia, malaria, Oroya fever), who are also more likely to develop a focal infection, such as infectious arthritis, osteomyelitis, pneumonia, endarteritis (eg, infected aortic aneurysm), endocarditis, urinary tract infection, cholangitis, or meningitis. Recurrent or multiple episodes of Salmonella infection in a patient without other risk factors should prompt HIV testing.

Salmonella (Skin Lesion)

Image

Photo courtesy of Dr. Thomas F. Sellers, Emory University, via the Public Health Image Library of the Centers for Disease Control and Prevention.

Focal infection can occur with or without sustained bacteremia, causing pain in or referred from the involved organ—the gastrointestinal tract (liver, gallbladder, appendix), endothelial surfaces (eg, atherosclerotic plaques, ileofemoral or aortic aneurysms, heart valves), pericardium, meninges, lungs, joints, bones, genitourinary tract, or soft tissues. Preexisting solid tumors are occasionally seeded and develop abscesses that may, in turn, become a source of Salmonella bacteremia. S. Choleraesuis and S. Typhimurium are the most common causes of focal infection.

• Cultures

Diagnosis of nontyphoidal Salmonella infections is by isolating the organism from stool or another infected site. In bacteremic and focal forms, blood cultures are positive, but stool cultures may be negative.

Antibiotic resistance has become a problem with both S. Typhi and nontyphoidal Salmonella, so antimicrobial susceptibility testing is important.

In patients with gastroenteritis, Salmonella

Patients at high risk (eg, older nursing home residents, infants, and patients with hemoglobinopathies, HIV infection, or other immunocompromising conditions) should be evaluated for complications (eg, typically blood culture and cerebrospinal fluid testing in infants).

• Supportive care

• Antibiotics for patients at high risk of invasive disease and patients with systemic or focal infections

• Sometimes surgery

Uncomplicated gastroenteritis due to nontyphoidal Salmonella infection is treated symptomatically with oral or IV fluids (see treatment of gastroenteritis).

Antibiotics do not hasten resolution of gastroenteritis, may prolong excretion of the organism, and are unwarranted in uncomplicated cases. However, in older nursing home residents, infants, and patients with hemoglobinopathies, HIV infection, or other immunocompromising conditions, increased mortality dictates treatment with antibiotics. Acceptable antibiotics include the following:

• TMP/SMX orally for children

Extraintestinal focal infections occur in 5 to 10% of patients with Salmonella bacteremia (1), necessitating additional evaluation and longer courses of antibiotics.

Patients who are not immunocompromised should be treated for 3 to 5 days; patients who have HIV/AIDS or other severely immunocompromising conditions may require prolonged suppression to prevent relapses.

Systemic or focal disease should be treated with antibiotic doses as for typhoid fever. Sustained bacteremia is generally treated for 4 to 6 weeks.

Abscesses should be drained surgically. At least 4 weeks of antibiotic therapy should follow surgery.

Infected aneurysms and heart valves and bone or joint infections usually require surgical intervention and prolonged courses of antibiotics.

The prognosis is usually good, unless severe underlying disease is present. Case fatality rates resulting from endocarditis and endarteritis are high.

Preventing contamination of foodstuffs by infected animals and humans is paramount. Preventive measures for travelers also apply to most other enteric infections.

Case reporting is essential.