Salmonella enterica subspecies enterica, a gram-negative, rod-shaped bacillus. 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 foods contaminated with animal feces. Transmission can also occur through direct contact with infected animals or their environment.
Nontyphoidal salmonellae are a leading cause of bacterial diarrhea worldwide; they are estimated to cause 94 million cases of gastroenteritis and 115,000 deaths globally each year. The risk of Salmonella infection among travelers returning to the United States varies by region of the world visited. In one analysis, the incidence of laboratory-confirmed infections from 2004 through 2009 was 7.1 cases per 100,000 among travelers to Latin American and 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. 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%).
The incubation period of nontyphoidal salmonellosis is 6–72 hours, and illness usually occurs within 12–36 hours after exposure. Illness is commonly manifested by acute diarrhea, with sudden onset of headache, abdominal pain, fever, and sometimes vomiting. The illness usually lasts 4–7 days, and most people recover without treatment. Salmonellosis outcomes differ by serotype. Approximately 5% of people develop bacteremia or focal infection (such as meningitis or osteomyelitis). 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.
Diagnosis is based on isolation of Salmonella organisms. About 90% of isolates are obtained from routine stool culture, but isolates are also obtained from blood, urine, and material from sites of infection. Isolates of salmonellae are needed for serotyping and antimicrobial susceptibility testing.
Current recommendations are to treat most patients with uncomplicated Salmonella infection with supportive therapy and no antimicrobial agents; however, many receive empiric therapy (or take self-treatment) without a stool culture. Antimicrobial therapy is recommended for gastroenteritis caused by Salmonella species in people at increased risk of invasive disease (infants aged <3 months, older adults aged ≥60 years, the debilitated or immunosuppressed) and patients with continued high fever or manifestations of extraintestinal infection. Fluoroquinolones are often employed for empiric treatment; azithromycin and rifaximin are also commonly used to treat travelers’ diarrhea. Resistance to antimicrobial agents varies by serotype and geographic region. Resistance to older antimicrobial agents (chloramphenicol, ampicillin, and trimethoprim-sulfamethoxazole) has been present for many years, and resistance to both fluoroquinolones and third-generation cephalosporins has been reported.
No vaccine is available against nontyphoidal Salmonella infection. Preventive measures are aimed at avoiding foods at high risk for contamination; frequent handwashing, especially after contacting animals or their environment; and taking additional food and water precautions while traveling (see Chapter 2, Food & Water Precautions).
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