The gram-negative bacteria Salmonella typically cause diarrhea and sometimes cause a more serious infection called typhoid fever.
People are usually infected when they eat contaminated food, such as undercooked chicken or eggs.
The bacteria usually infect the digestive tract but can travel through the bloodstream and infect other parts of the body.
People have nausea and crampy abdominal pain, followed by watery diarrhea, fever, and vomiting.
Identifying the bacteria in a sample, usually of stool, confirms the diagnosis.
Lost fluids are replaced.
Antibiotics are usually not helpful for people who have inflammation of the stomach and intestines that results in diarrhea (gastroenteritis), but antibiotics are helpful for people who are at risk of or have bacteremia, certain other infections, or an abscess.
(See also Overview of Bacteria.)
There are over 2,500 different types of Salmonella bacteria.
Salmonella bacteria cause several types of infection. Most often, these bacteria cause gastroenteritis, but they sometimes cause typhoid fever, a more serious infection.
Some Salmonella reside only in people. Other species of Salmonella normally reside in the digestive tract of many wild and domestic animals, such as cattle, sheep, pigs, fowl, reptiles (such as snakes and lizards), and amphibians (such as turtles). Many of these can cause infections in people.
Salmonella bacteria are excreted in the feces of infected animals and people, leading to contamination. In the United States during the 1970s, many infections were spread by pet turtles, so a law was created to ban the sale of turtles that have a shell less then 4 inches (10.5 centimeters) long. The law resulted in a decline in infections. However, turtles are still sold illegally and still cause infections in people. Up to 90% of pet reptiles, such as snakes and lizards, and possibly amphibians (depending on the species), such as aquatic frogs, are infected with Salmonella.
People are usually infected by eating undercooked poultry or eggs but sometimes by eating undercooked beef and pork, unpasteurized dairy products (such as raw milk), or contaminated seafood or fresh produce. Salmonella bacteria can infect the ovaries of hens and thus infect the egg before the egg is laid. Other foods may be contaminated by animal feces (for example, in slaughterhouses) or by infected food handlers who do not adequately wash their hands after using a toilet. People can also become infected if they drink contaminated water.
Other reported sources of infection are carmine red dye and contaminated marijuana.
Because stomach acid tends to destroy Salmonella, a large number of these bacteria must be consumed for infection to develop, unless people have a deficiency of stomach acid. Such a deficiency may occur in
Children under 1 year old
Older adults
People who had part of their stomach surgically removed
Salmonella bacteria cause inflammation of the intestine (gastroenteritis) and thus are a common cause of diarrhea.
Did You Know...
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Spread through the bloodstream
Sometimes the bacteria enter the bloodstream (causing bacteremia) and spread, causing infections or collections of pus (abscesses) at distant sites, such as the bones, joints, urinary tract, and lungs. Bacteria may collect and cause infection on artificial (prosthetic) joints or heart valves, on a blood vessel graft, or on tumors. The lining of arteries, usually the aorta (the largest artery in the body), may be infected. Abscesses and infected arteries can cause chronic bacteremia.
The infection is more likely to spread through the bloodstream in the following people:
Infants
Older adults, especially those living in a nursing home
People with disorders that affect red blood cells, such as sickle cell anemia or malaria
People with a disorder that weakens the immune system, such as human immunodeficiency virus (HIV) infection or cancer
People who take medications that suppress the immune system, such as those used to treat cancer or prevent rejection of an organ transplant
Symptoms of Salmonella Infections
When the intestine is infected, symptoms of gastroenteritis usually start 12 to 48 hours after the bacteria are ingested. These symptoms include nausea and crampy abdominal pain soon followed by watery diarrhea, fever, and vomiting. Symptoms resolve in 1 to 4 days. Occasionally, symptoms are more severe and last a long time.
Long after symptoms are gone, a few people continue to excrete the bacteria in their stool. Such people are called carriers.
About 10 to 30% of adults develop reactive arthritis weeks to months after diarrhea stops. Reactive arthritis causes pain and swelling, usually in the hips, knees, and Achilles tendon (which connects the heel bone and calf muscle).
Other symptoms may develop if bacteremia develops and infection spreads. For example, if a bone is infected, the area over it is often tender or painful. If a heart valve is infected, people may feel short of breath. If the aorta is infected, the back and abdomen may be painful.
People usually recover well. Exceptions are people who had a disorder, particularly one that weakens the immune system, before the Salmonella infection or who have a complication caused by the infection.
Diagnosis of Salmonella Infections
Culture of stool, pus, blood, or a sample from the rectum
To diagnose a Salmonella infection, doctors take a sample of stool, pus, or blood or use a swab to obtain a sample from the rectum. The sample is sent to a laboratory where bacteria, if present, can be grown (cultured). Identifying the bacteria in the sample confirms the diagnosis.
Bacteria are also tested to see which antibiotics are effective (a process called susceptibility testing).
Tests are also sometimes done (for example, in people who have gastroenteritis) to identify the genetic material of the bacteria.
People who have risk factors for bacteremia may have additional testing done to identify complications of the infection.
Treatment of Salmonella Infections
For gastroenteritis, fluids
For people who are at risk of serious infection or who have bacteremia or another infection, antibiotics
For abscesses, surgical drainage and antibiotics
People with gastroenteritis
People with bacteremia
Abscesses are drained surgically, and antibiotics are given for several weeks.
If the aorta, a heart valve, or other areas (such as joints) are infected, surgery is usually required, and antibiotics are given for weeks or months.
Prevention of Salmonella Infections
Ways to prevent Salmonella infections include
Thoroughly cooking poultry, eggs, and ground beef
Not eating or drinking foods that contain raw eggs or raw (unpasteurized) milk, such as cookie dough, Hollandaise sauce, or certain homemade salad dressings
Thoroughly washing produce
Washing hands after going to the toilet or changing a diaper
Washing hands, kitchen work surfaces, and utensils with soap and water immediately after they have touched raw meat or poultry
Washing hands with soap after touching amphibians, reptiles, birds, or baby chicks and after contact with feces of a pet
Special precautions are needed for people at high risk, such as young children. For example, because reptiles, amphibians (such as turtles), chicks, and other young birds are particularly likely to have Salmonella, young children should not be allowed to handle these animals, and reptiles and amphibians should not be in the same house as infants.
Infected people should not prepare food for others.
Travelers can take certain measures to help reduce the risk of developing diarrhea.
There is no vaccine to prevent salmonellosis, although there are vaccines for typhoid fever.
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
Centers for Disease Control and Prevention (CDC): Salmonella: A resource providing information about Salmonella, including outbreaks and prevention
