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Salmonella: Symptoms, Causes, Prevention, and Treatment

June 30th, 2008

salmonella-bacterium.jpgWith salmonella-related stories making their way into the news recently, I figured that it was time for me to put together an article on the subject. This essay will summarize and describe the recent news, causes, symptoms, prevention, and treatment of infections related to this species of bacteria. The picture to the left is a magnified electron microscope image of what a single salmonella bacterium looks like. The scaling used is one micrometer, which is one millionth of a meter or one thousandth of a millimeter.

Recent News

The Center for Disease Control says the current outbreak, as of June 27, 2008, is linked to a rare form of bacteria called Salmonella Saintpaul. Thus far, it has spread to include 810 cases in 36 states and the District of Columbia. The specific source of the outbreak has not been found. Cherry tomatoes, grape tomatoes, homegrown tomatoes, and those sold with the vine still attached are considered safe, but health authorities are advising people to avoid eating raw Roma or red round tomatoes. However, tomatoes cooked to 145 degrees for 15 seconds will kill the bacteria, which generally causes fever, diarrhea and abdominal cramping. The outbreak, which has affected several types of tomatoes, has hit hardest in New Mexico and Texas.

What is Salmonella?

Salmonella is a bacterial infection that lives in the intestinal tracts of humans and other animals. Bacteria are transmitted to humans when they eat foods contaminated with animal feces. Salmonella bacteria are subdivided into serotypes based upon their biochemical properties. Although salmonellosis can occur throughout the year, most cases occur during the summer months.

Several people have asked about the color of the salmonella bacterium itself. This can be somewhat difficult to track down because most images show the specimens only after they have been treated with some type of colored dye or other agent. It turns out that natural salmonella are nearly colorless but are opaque and can be seen on a nutrient plate after sufficiently large colonies have been nurtured. For an image of what plain salmonella looks like, see this picture from MicrobeLibrary.org.

Prevalence of Salmonella

In terms of officially reported and culture-confirmed cases, salmonella sickens about 40,000 people a year in the United States. However, the Division of Bacterial and Mycotic Diseases (DBMD, a division of the Center for Disease Control) estimates that actual number of annual infections is closer to 1.4 million. This is due to the fact that most infections are not reported unless the symptoms become severe and require some form of medical treatment. DBMD estimates that approximately 1,000 deaths occur each year from salmonella-related food poisoning. Most of the deaths are among people with weaker immune systems such as the elderly or very young.

Food Sources of Salmonella Infection

Contaminated meat products (for example, poultry, burgers, or sausages) are the main sources of infection from food. Agricultural products such as tomatoes or other vegetables may also be significant sources of infection, particularly if the crops are sprayed with some type of manure that may be carrying the bacteria. Cross-contamination of vegetable crops while in storage or distribution is also possible. Unpasteurized milk or other dairy products presents another source of infection in areas of the world where pasteurization is not always practiced.

Animal Sources of Salmonella

Salmonella is particularly severe in young, debilitated, or stressed animals. In birds, a common source is salmonella typhimurium from rodent droppings. This species is a serovar of salmonella enterica and is also the cause of typhoid fever. Reptiles, baby chicks and ducklings, and small rodents such as hamsters are particularly likely to carry salmonella. You should always wash your hands immediately after handling one of these animals, even if the animal is healthy. Reptiles can be safely kept as pets, but reptile owners should be aware of the methods for reducing their risk of acquiring salmonella bacteria from their reptiles. Salmonella organisms have been found in the stools of sick and apparently healthy people and animals. Most domestic animals, including ducks, cattle, swine, dogs, cats, pet turtles, and chicks have been found to carry and transmit these pesky bacteria.

Salmonella Symptoms

Infection with the salmonella bacteria produces an illness called salmonellosis. According to the CDC, most infected people develop diarrhea, fever, and abdominal cramps within 12 to 72 hours. Officials recommend consulting a health care provider if diarrhea lasts longer than two days in an adult, one day in a child younger than 4, or eight hours in an infant. Serious — and potentially fatal — cases are more likely in young children, frail or elderly people, and people with weak immune systems.

Complications - Reiter’s Syndrome

Contaminated peanut butter has also been linked to a complication of salmonella infection called Reiter’s syndrome, a reactive arthritis marked by inflammation of the joints. The condition occurs after bacteria, in this case salmonella, travels through the body to a joint or joints. Reiter’s syndrome also produces two other seemingly unrelated symptoms: redness of the eyes and urinary tract problems such as an increased need to urinate or burning sensations near the genital areas. It can be treated with anti-inflammatory drugs or steroid injections into the affected joints to reduce the pain and swelling. Less severe cases can be treated with anti-inflammatory over-the-counter drugs such as aspirin or ibuprofen. Otherwise treatment methods are the same as with other forms of salmonella infection. Full recovery time for Reiter’s syndrome is generally 2 to 6 months.

Salmonella Treatment

In most cases, the infection resolves itself without treatment when the bacteria are passed out of a person’s intestines through the stool. If symptoms are particularly severe and there is significant risk of mortality, antibiotics may be administered to eliminate the bacteria. However, antibiotics do not shorten recovery time and can also prolong the excretion of bacteria in the stool. Moreover, the organism has become resistant to a wide range of anti-infectious agents, making it more difficult to treat. Therefore, antibiotics are not usually given unless medically necessary in order to prevent the problem of drug-resistant bacteria.

Prevention - How to Prevent Salmonella

In order to avoid the disease, wash your hands thoroughly after handling an animal and ensure that no reptiles are permitted to come into contact with an infant. Even healthy reptiles (especially turtles and iguanas) are not appropriate pets for small children and should not be in the same house as an infant.

With regard to suspicious foods, vigorous washing can reduce the risk of infection, but as a precaution the FDA urges consumers to simply avoid eating any suspect foods altogether unless they are properly cooked. Cooking fresh vegetables and fruits eliminates the salmonella bacteria entirely. Cooking reduces the number of bacteria present in an egg; however, an egg with a runny yolk still poses a greater risk than a completely cooked egg. Undercooked egg whites and yolks have been associated with outbreaks of salmonella enteritidis infections.

It is also important to prevent contamination of prepared food from any utensils, cutting surfaces, or other implements that may have been in contact with raw poultry, eggs, or any other suspected salmonella source. Hands, dishes, and cutting surfaces should be thoroughly washed before preparing any type of food that will not be cooked (for example, salads). Also, if you happen to be in the position of caring for an animal or person who may be infected with salmonella, promptly discard or launder any material that becomes contaminated with their stool (feces) and wash your hands before handling any food items. Overall, prevention of salmonella infection is a matter of practicing good hygiene and common sense.

3 Responses to “Salmonella: Symptoms, Causes, Prevention, and Treatment”

  1. comment number 1 by: ameo

    really hepful info ,
    and i think the best way is just getty away from Salmonella by washing
    really good .. washing everything

  2. comment number 2 by: Anonymous


  3. comment number 3 by: edena

    u should make more articals

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