1. Basic Facts About Salmonella
What Is Salmonella?
Salmonellosis, or salmonella, is an illness caused by rod-shaped, gram-negative bacteria of the genus Salmonella. The species most often responsible for illness in people is Salmonella enterica (S. enterica), which is found in warm-blooded mammals and the environment. The most common form of salmonellosis is a foodborne illness that results from an infection of the gastrointestinal tract. However, in some parts of the world, the S. enterica serotype Typhi can invade the bloodstream and cause a severe and occasionally life-threatening infection known as typhoid fever.
Symptoms of a foodborne salmonella infection include vomiting, diarrhea, abdominal cramps and fever. They can appear within 12 to 72 hours after infection. In most people, the illness lasts anywhere from four to seven days and usually resolves without treatment. However, the very young, the elderly and those with chronic health conditions or compromised immune systems are more susceptible to infection, and the illness may be more severe, leaving them at risk of dehydration.¹
Symptoms of typhoid fever may not appear until six to 30 days after infection and include weakness, a very high and persistent fever, constipation, headaches and, in some people, a skin rash. Diarrhea is uncommon and vomiting not severe. Symptoms may last for several months if left untreated. It is most common in people who have traveled in countries where hygiene standards are low and where food and drinking water may be contaminated.²
Who Is at Risk?
Anyone is at risk of a foodborne illness caused by salmonella, but children under 5 are at an increased risk and have the highest incidence in the U.S. The percentage of those with severe infections that require hospitalization is highest among the elderly, and deaths in this group are also highest.³ As with many infections, people with chronic conditions or compromised immune systems — such as people with HIV, diabetes, rheumatological conditions or sickle cell disease, and those using corticosteroids — may be at an increased risk of serious illness from salmonella infections.⁴ Other groups with an increased risk of contracting a salmonella infection include infants who are not breastfeeding⁵ and people using medications that can reduce stomach acid production.⁶
How Are Salmonella Infections Diagnosed?
Because the symptoms of salmonella are vague and can be caused by a variety of infections, a laboratory diagnosis is required to confirm the presence of Salmonella bacteria. The testing process involves trying to grow the bacteria from a sample of stool, blood or other specimen. Salmonella that grow are considered “culture confirmed” and may then be subjected to a range of biochemical tests to identify the specific subspecies.⁷ The initial testing and confirmation of salmonella may be done by a hospital’s clinical diagnostic laboratory, but further identification is often done by a state or territorial public health laboratory. Data on salmonella outbreaks and cases is collected by the U.S. Centers for Disease Control and Prevention (CDC) as part of its regular enteric disease surveillance.⁸