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Salmonella Infections

by Larry M. Bush, MD

Salmonella infections are caused by the gram-negative bacteria Salmonella.

  • 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, and antibiotics are usually not helpful for salmonellal intestinal infections.

Salmonella bacteria cause several types of infection. Most often, these bacteria cause gastroenteritis, but they sometimes cause typhoid fever, a more serious infection.

There are different types of Salmonella bacteria. Two species cause typhoid fever:

  • Salmonella typhi

  • Salmonella paratyphi

Salmonella typhi reside only in people. Salmonella paratyphi reside mainly in people but sometimes in domestic animals. Other species of Salmonella normally reside in the digestive tract of many wild and domestic animals, such as cattle, sheep, pigs, fowl, and reptiles (including snakes, lizards, and turtles). Many of these can cause infections in people. Two species —Salmonella enterica serotype Typhimurium and Salmonella serotype Enteritidis—cause most Salmonella infections in the United States.

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 their sale was prohibited, resulting in fewer infections. Recently, the legal and illegal sale of pet reptiles has increased. Up to 90% of pet reptiles and amphibians, such as aquatic frogs, are infected with Salmonella.

People are infected usually by eating undercooked poultry or eggs but sometimes by eating undercooked beef and pork, unpasteurized dairy products, 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.

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 people

  • People taking antacids or drugs that inhibit stomach acid production, including histamine-2 (H 2 ) blockers (such as ranitidine) or proton pump inhibitors (such as omeprazole)

The bacteria cause inflammation of the intestine ( gastroenteritis) and thus are a common cause of diarrhea.

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:

  • Infants

  • Older people, 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

  • People who take drugs that suppress the immune system, such as those used to treat cancer or prevent rejection of an organ transplant

Symptoms

When the intestine is infected, symptoms usually start 12 to 48 hours after the bacteria are ingested. Nausea and crampy abdominal pain occur, soon followed by watery diarrhea, fever, and vomiting. Salmonella 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.

Up to about 30% of adults develop reactive arthritis weeks to months after diarrhea stops. This disorder 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.

Did You Know...

  • In the United States, up to 90% of pet reptiles and amphibians are infected with Salmonella.

Diagnosis

  • Culture of stool, pus, blood, or a sample from the rectum

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 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).

Prevention

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 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 (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 should not be in the same house as infants.

Infected people should not prepare food for others.

There is no vaccine to prevent salmonellosis, although there are vaccines for typhoid fever.

Treatment

  • For intestinal infection, fluids

  • For people who are at risk of or have bacteremia, antibiotics

  • For abscesses, surgical drainage

The intestinal infection is treated with fluids given by mouth or, for severe infection, intravenously.

Antibiotics do not shorten recovery time and may result in bacteria being excreted in the stool longer. Therefore, antibiotics are usually not given.

However, people at risk of bacteremia (such as older residents of a nursing home and people with HIV infection) and people with implanted devices or materials (such as an artificial joint or heart valve or a blood vessel graft) are given antibiotics. They may be given ciprofloxacin or azithromycin for several days.

People with bacteremia are given antibiotics such as ciprofloxacin or ceftriaxone intravenously for 2 weeks. If bacteremia persists, antibiotics are given for 4 to 6 weeks.

Abscesses are drained surgically, and antibiotics are given for at least 4 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.

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Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • ZANTAC
  • PRILOSEC
  • CILOXAN, CIPRO
  • ZITHROMAX
  • ROCEPHIN