Salmonella enterica subspecies enterica is a gram-negative, rod-shaped bacillus. More than 2,500 Salmonella serotypes have been identified. Nontyphoidal salmonellosis refers to illnesses caused by all serotypes of Salmonella except for Typhi, Paratyphi A, Paratyphi B (tartrate negative), and Paratyphi C.
Usually through the consumption of food or water contaminated with animal feces. Transmission can also occur through direct contact with infected animals or their environment and directly between humans.
Nontyphoidal salmonellae are a leading cause of bacterial diarrhea worldwide; they are estimated to cause approximately 153 million cases of gastroenteritis and 57,000 deaths globally each year. The risk of Salmonella infection among travelers returning to the United States varies by region of the world visited. The incidence of laboratory-confirmed infections from 2004 through 2009 was 7.1 cases per 100,000 among travelers to Latin America and the Caribbean, 5.8 cases per 100,000 among travelers to Asia, and 25.8 cases per 100,000 among travelers to Africa. The true number of illnesses is much higher, because most ill people do not have a stool specimen tested. US travelers with salmonellosis were most likely to report visiting the following countries: Mexico (38% of travel-associated salmonellosis), India (9%), Jamaica (7%), the Dominican Republic (4%), China (3%), and the Bahamas (2%); these findings are influenced by the number of travelers to different destinations. A systematic review of travelers’ diarrhea etiology studies published from 2002 through 2011 found that Salmonella was detected in <5% of patients who had traveled to Latin America, the Caribbean, and South Asia and in 5%–15% of patients who had traveled to Africa or Southeast Asia. Salmonella infection and carriage have been reported among internationally adopted children.
Gastroenteritis is the most common clinical presentation of nontyphoidal Salmonella infection. The incubation period is typically 6–72 hours; while atypical, illness has been documented even 14 days after exposure. Illness is commonly manifested as acute diarrhea, abdominal pain, fever, and sometimes vomiting. The illness usually lasts 4–7 days, and most people recover without treatment. Approximately 5% of people develop bacteremia or focal infection (such as meningitis or osteomyelitis). Salmonellosis outcomes differ by serotype. Infections with some serotypes, including Dublin and Choleraesuis, are more likely to result in invasive infections. Rates of invasive infections and death are generally higher among infants, older adults, and people with immunosuppressive conditions (including HIV), hemoglobinopathies, and malignant neoplasms. Infection with antibiotic-resistant organisms has been associated with a higher risk of bloodstream infection and hospitalization.
Culturing organisms continues to be the mainstay of clinical diagnostic testing for nontyphoidal Salmonella infection. Approximately 90% of isolates are obtained from routine stool culture, but isolates are also obtained from blood, urine, abscesses, cerebrospinal fluid, and other sites of infection. Although culture-independent diagnostic tests are increasingly used by clinical laboratories to diagnose Salmonella infection, isolates are needed for serotyping and antimicrobial susceptibility testing. Salmonella isolate submission requirements vary by state, but most states mandate that Salmonella isolates or clinical material be submitted to the local or state public health laboratory. To understand submission requirements in a particular state, clinical laboratories are advised to review the disease reporting and mandatory isolate submission regulations of that state. Salmonellosis is a nationally notifiable disease.
Current recommendations are to treat most patients with uncomplicated Salmonella infection with oral rehydration therapy but not with antimicrobial agents. Antimicrobial therapy should be considered for patients who are severely ill (for example, those with severe diarrhea, high fever, or manifestations of extraintestinal infection) and for people at increased risk of invasive disease (infants, older adults, and the debilitated or immunosuppressed). When antimicrobial therapy is indicated, empiric treatment is usually required until susceptibility data are available. Resistance to antimicrobial agents varies by serotype and geographic region. Fluoroquinolones are considered first-line treatment in adult travelers. However, resistance to fluoroquinolones among Salmonella strains is rising globally. In a study of international travelers diagnosed with S. enterica serotype Enteritidis infection in the United States, 24% of isolates showed decreased susceptibility to fluoroquinolones compared with only 3% of isolates from patients with no history of international travel. Azithromycin can be used for children and is an alternative agent for adults returning from Latin America or Asia, where resistance in this organism to fluoroquinolones may exceed 10%. Azithromycin resistance has been documented in multiple settings globally but is not commonly reported. Resistance to older antimicrobial agents (chloramphenicol, ampicillin, and trimethoprim-sulfamethoxazole) has been present for many years; these should not be considered first-line empiric agents in returning travelers (see Chapter 2, Travelers’ Diarrhea).
No vaccine is available against nontyphoidal Salmonella infection. Preventive measures are aimed at avoiding foods and drinks at high risk for contamination; frequent handwashing, especially after contacting animals or their environment; and taking food and water precautions (see Chapter 2, Food & Water Precautions).
CDC website: www.cdc.gov/salmonella
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Jennifer C. Hunter, Louise K. Francois Watkins