Nontyphoidal Salmonella Infections
(See also Overview of Salmonella Infections.)
Nontyphoidal Salmonella infections are common and remain a significant public health problem in the US. Many serotypes of Salmonella have been given names and are referred to informally as if they were separate species even though they are not. Most nontyphoidal Salmonella infections are caused by S. enterica subspecies enterica serotype Enteritidis, S. Typhimurium, S. Newport, S. Heidelberg, and S. Javiana.
Human disease occurs by direct and indirect contact with numerous species of infected animals, the foodstuffs derived from them, and their excreta. Contaminated meat, poultry, raw milk, eggs, egg products, and water are common sources of Salmonella. Other reported sources include infected pet turtles and reptiles, carmine red dye, and contaminated marijuana.
Each Salmonella serotype can cause any or all of the clinical syndromes described below, although given serotypes tend to produce specific syndromes. Enteric fever, for instance, is caused by S. Paratyphi types A, B, and C.
An asymptomatic carrier state may also occur. However, carriers are rare and do not appear to play a major role in large outbreaks of nontyphoidal gastroenteritis. Persistent shedding of organisms in the stool for ≥ 1 year occurs in only 0.2 to 0.6% of patients with nontyphoidal Salmonella infections.
Salmonella infection may manifest as
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. This disorder causes pain and swelling, usually in the hips, knees, and Achilles tendon.
Enteric fever is a less severe form than typhoid; it is characterized by fever, prostration, and septicemia.
Bacteremia is relatively uncommon in patients with gastroenteritis, except in infants and older people. 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. Patients may have recurrent episodes of bacteremia or other invasive infections (eg, septic arthritis) due to Salmonella. Recurrent or multiple episodes of Salmonella infection in a patient without other risk factors should prompt HIV testing.
Focal Salmonella 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.
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 is more common with nontyphoidal Salmonella than with S. Typhi, and antimicrobial susceptibility testing is important.
In patients with gastroenteritis, stool specimens stained with methylene blue often show white blood cells, indicating inflammatory colitis.
Uncomplicated gastroenteritis due to nontyphoidal Salmonella infections 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 antibiotic regimens include the following:
Nonimmunocompromised patients should be treated for 3 to 5 days; patients with AIDS 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 week 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.
Asymptomatic carriage is usually self-limited, and antibiotic treatment is rarely required. In unusual cases (eg, in food handlers or health care workers), eradication may be attempted with oral ciprofloxacin 500 mg every 12 hours for 1 month. Follow-up stool cultures should be obtained in the weeks after drug administration to document elimination of Salmonella.
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.
Nontyphoidal Salmonella infections are common and result from direct and indirect contact with numerous species of infected animals, the foodstuffs derived from them, and their excreta.
Clinical syndromes include gastroenteritis, enteric fever, and focal infections; bacteremia occasionally occurs.
Diagnose using cultures.
For uncomplicated gastroenteritis, antibiotics are unnecessary; they do not hasten resolution and may prolong excretion of the organism.
Treat high-risk patients (eg, older nursing home residents, infants, patients with hemoglobinopathies, HIV infection, or other immunocompromising conditions) with antibiotics, such as ciprofloxacin, azithromycin, ceftriaxone, or trimethoprim/sulfamethoxazole (TMP/SMX).
An asymptomatic carrier state may occur, but carriers do not play a major role in outbreaks, and treatment with antibiotics is rarely indicated.