Salmonella Infections (Including Enteric Fever)

Definition

Many of the more than 2500 serovars (also called serotypes) of Salmonella enterica subspecies enterica infect humans and cause a range of clinical conditions from asymptomatic intestinal carriage to intestinal infection to invasive disease with extraintestinal complications. Each serovar designation follows the species name (e.g., Salmonella enterica subspecies enterica serovar Typhimurium) and is frequently abbreviated as simply Salmonella followed by the serovar name (e.g., Salmonella Typhimurium).

Epidemiology

Salmonella Typhi, Salmonella Paratyphi A, Salmonella Paratyphi B, Salmonella Paratyphi C, and Salmonella Sendai are either solely or almost exclusively pathogens of humans; they cause primarily enteric fever rather than diarrhea, and transmission is usually through water or food. As a result of modern sewage and water treatment facilities, as well as improved food safety practices, typhoid fever and paratyphoid fever have become rare in high-income countries, but they remain a problem in countries that lack adequate sanitation and a safe water supply. Fewer than 500 cases of typhoid fever are usually reported annually in the United States, and most of those infections were acquired abroad. In contrast, an estimated 10.9 million typhoid illnesses occurred globally in 2017 and caused more than 135,000 deaths. ^, Nontyphoidal Salmonella serovars are a leading cause of community-onset bloodstream infection in sub-Saharan Africa, where children younger than 3 years and HIV-infected adults carry most of the burden of invasive disease.

Other serovars of Salmonella (described here as nontyphoidal Salmonella ) have reservoirs in warm-blooded animals and cause human illness after the consumption of contaminated meat or animal products, contamination of produce or water by animal feces or animal products, or exposure to animals and their environments. Some nontyphoidal Salmonella serovars appear frequently in particular animal species, and about 10% of Salmonella infections may be attributable to animal exposure, including small pet turtles. Salmonella Enteritidis has a reservoir in chickens, and infection is often linked to the consumption of undercooked eggs and poultry products or to exposure to live chicks. Such a relationship is less clear for some other nontyphoidal serovars (e.g., Salmonella Typhimurium). Foodborne nontyphoidal Salmonella is estimated to be associated with approximately 1 million domestically acquired illnesses and about 450 deaths annually in the United States, and it is the leading cause of foodborne outbreaks of enterocolitis in the European Union. In the United States, a disproportionate number of infections occur in July through October, probably related to warm weather. Salmonella infections are most common among infants and children younger than 5 years of age. Worldwide, nontyphoidal Salmonella causes an estimated 150 million illnesses and 50,000 to 60,000 deaths per year, with about 50% of these estimated to be foodborne.

Salmonellae are transmitted by the ingestion of fecally contaminated food or water; contact with animals, their environments, and other fomites; and, rarely, close contact with infected persons (e.g., oral-anal intercourse). The ultimate sources of contamination are humans or animals that are acutely ill or are shedding the organism without symptoms.