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INTRODUCTION

Salmonellosis is the general term for infection caused by bacteria in the genus Salmonella, excluding Salmonella Typhi and three other typhoidal bioserotypes (i.e., Paratyphi A, Paratyphi B tartrate-negative, and Paratyphi C) that cause typhoid or enteric fever. Salmonellosis is a common gastrointestinal infection in the United States and around the world. Each year, an estimated 1.22 million Salmonella infections occur in the United States, and approximately 150 foodborne outbreaks of salmonellosis are investigated and reported by public health officials1,2 (Fig. 111-1). Large and severe outbreaks of salmonellosis have driven major advances in public health surveillance and prevention, such as routine serotyping of clinical isolates in public health laboratories to determine major strains responsible for illness and to detect outbreaks.3 The many types of Salmonella have become adapted to number of different host animals, particularly reptiles, amphibians, birds, and a variety of mammals, in which they usually cause little observed illness. Part of the adaptation includes strategies to reach the next generation of hosts by silently contaminating fertile eggs or mammalian milk. Humans can encounter the bacteria in their food supply, in water or other environmental sources, and through direct contact with animals carrying it.

FIGURE 111-1

Reported combined incidence of typhoid fever and nontyphoidal salmonellosis (confirmed and suspected) in the United States from 1920 to 2015.

Most illnesses caused by nontyphoidal Salmonella are characterized by diarrhea, sometimes bloody, along with fever, abdominal cramps, and vomiting, which can last for several days to a week, and usually resolves without antibiotic treatment. Symptoms typically begin 24–48 hours after ingesting the bacteria, as early as 8 hours and as late as 92 hours, and sometimes longer.4 Some infections can lead to bloodstream invasion with a clinical picture more like that of typhoid fever, with high fever, sometimes complicated by sepsis, shock, organ failure, and death; in these patients, antibiotic treatment can be lifesaving. These invasive infections more commonly occur in persons with deficient immunity due to malignancy, medical treatment, diabetes, hemoglobinopathy, or HIV infection; recurrent Salmonella bacteremia is a defining condition for AIDS. Some serotypes, including Typhimurium and Enteritidis, are opportunistically invasive, and are particularly likely to cause bacteremia in persons with AIDS.5 Other serotypes, such as Dublin, Choleraesuis, and Heidelberg are more likely to be invasive even in the normal host.6 The likelihood of bacteremia depends on the dose ingested; persons with normal immunity may develop bacteremia following an overwhelming dose. In young infants, febrile bacteremia is not an uncommon outcome. Salmonella can also spread from the GI tract to distant parts of the body, leading to focal infections such as osteomyelitis, meningitis, and urinary tract infections. There is little apparent lasting immunity following natural infection, and humans infected with one strain remain susceptible to infection with others.

DIAGNOSIS

Salmonellosis is ...

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