What Is Salmonella? What Is Salmonella Infection?

Salmonella infection, or salmonellosis, is a bacterial disease of the intestinal tract. Salmonella is a group of bacteria that cause typhoid fever, food poisoning, gastroenteritis, enteric fever and other illnesses. People become infected mostly through contaminated water or foods, especially meat, poultry and eggs.

Salmonella is a gram-negative, rod-shaped bacilli that can cause diarrheal illness in humans. Put simply - Salmonella is a bacterium shaped like a rod with a cell wall composed of peptidoglycan.

Gram-negative is a term used in bacteriology for bacteria that lose the crystal violet stain and take the color of the red counterstain in Gram's method of staining. Gram-negative bacteria usually have a cell wall composed of a thin layer of peptidoglycan. Bacilli is the plural of bacillus. Bacteria that have a rod-like shape are called bacilli.

The Salmonella family includes over 2,300 serotypes of bacteria - they are microscopic one-celled organisms. Salmonella enteritidis and Salmonella typhimurium are responsible for over 50% of all human infections in the USA. Some Salmonella strains that exist in humans can make animals sick, and vice-versa. The bacteria live in the gut of infected humans and animals.

What is salmonellosis?

Salmonellosis is an infection caused by Salmonella. Approximately 1.4 million Americans are affected with salmonellosis every year, of which about 500 die, according to the CDC (Centers for Disease Control and Prevention). In 2004 US authorities announced that Salmonella was responsible for 42% of human bacterial infections, followed by Campylobacter 37%, Shigella 15%, E. coli O157:H7 2.6%.

According to the HPA (Health Protection Agency), in 2008 9,864 people were affected with salmonellosis in the UK. In most of Western Europe, in countries such as the UK, France, Germany, Scandinavia, Holland, Switzerland and Belgium, the incidence of salmonellosis is very much lower than in the USA.

What causes Salmonella infections (salmonellosis)?

Salmonella live in the intestines of birds, animals and humans. Most human infections are caused by eating food or drinking water that has been contaminated by feces (excrement). Foods that are most commonly infected are:
  • Uncooked meat, seafood and poultry - contamination most commonly occurs during the slaughtering process. Harvesting seafoods in contaminated waters is also a common cause.
  • Uncooked eggs - the Salmonella are usually present in the eggs when laid if the chicken is infected. Raw eggs may be found in some types of mayonnaise and homemade sauces.
  • Fruits and vegetables - if fruit and vegetables have been watered or washed in contaminated water there is a much higher chance they will be contaminated. Some kitchen practices may contaminate fruits and vegetables - if the person preparing the food handles raw meat and then touches the fruit without washing his/her hands, for example.
  • Lack of hygiene - kitchen surfaces that are not kept clean, lack of handwashing procedures during food preparation, and lack of handwashing after going to the toilet or changing a baby's diapers, are common routes for contamination and infection. A person with contaminated hands can pass the infection on to other people by touching them, or touching surfaces which others then touch.
  • Pet reptiles or amphibians - most reptiles and amphibians carry Salmonella in their gut without becoming ill. They shed the bacteria in their droppings, which can quickly spread onto their skin and then anything they come into contact with, including cages, toys, clothes, furniture and household surfaces. The Health Protection Agency (UK) advises families not to keep reptiles if there are children under 5, pregnant women, very elderly people, and/or people with weaker immune systems in the household.

What are the signs and symptoms of salmonellosis (Salmonella infection)?

Out of the thousands of types of Salmonella bacteria, only about twelve make people ill, usually with gastroenteritis. A smaller number cause typhoid fever, which can be a very serious and potentially fatal disease, especially in developing countries.
A sign is something the doctor can see or touch, such as a rash, while a symptom is something the patient feels, such as dizziness or headache.

Salmonella-induced Gastroenteritis signs and symptoms:
  • Stomach cramps
  • Bloody stools
  • Chills
  • Diarrhea
  • Fever
  • Headache
  • Muscle pains
  • Nausea
  • Vomiting
Salmonella-induced Typhoid fever signs and symptoms:

People who live in developed countries most commonly become infected when they travel abroad. The incubation period - time between becoming infected and symptoms appearing - is usually between 7 to 14 days. If Typhoid fever is left untreated symptoms develop over a course of four weeks, with additional symptoms appearing each week. The vast majority of patients respond rapidly to treatment and should not experience all the symptoms below if they receive treatment:
  • Typhoid symptoms during week 1

    • A dull headache in the front of the head.
    • A skin rash of pink spots.
    • Abdominal pain.
    • A progressive feeling of not being well.
    • Constipation or diarrhea (constipation more likely with adults, diarrhea more likely with children).
    • Mental confusion (delirium).
    • Dry cough.
    • A fever which usually rises to about 39-40c (103-104f) and settles there.
    • Vomiting (more common in children).
  • Additional typhoid symptoms during week 2 if left untreated:

    • Swelling of the abdomen.
    • Heart beat slows down.
  • Additional typhoid symptoms during week 3 if left untreated:

    • Weight loss.
    • Loss of appetite.
    • Exhaustion.
    • Yellow-green watery diarrhea, which usually has a foul smell.
    • Swelling of abdomen continues and becomes severe.
    • Panting.
    • Severe confusion, apathy, in some cases psychosis.
    • 10%-15% of patients go on to develop the following life-threatening complications
    • Internal bleeding.
    • Rupturing or splitting of the bowel.
    • Myocarditis (inflammation of the myocardium, the heart muscle).
    • Multiple organ failure as the bacteria start releasing toxins.
  • Persistent typhoid symptoms during and after week 4

      If the patient receives treatment and the complications responded to treatment, he/she has a good chance of making a recovery. However, weight loss and exhaustion may persist for some months.

How is Salmonella infection diagnosed?

Typically, diarrhea and vomiting are indicative of gastroenteritis, and there are no specific diagnostic tests required for most patients with the condition. A doctor will often take a detailed history concerning medical treatments, diet changes or food preparation habits, and travel destinations in his/her efforts to find the underlying illness and nature of the pathogen. A physical examination will be employed to be sure that the symptoms are not due to an infection such as appendicitis, gallbladder disease, pancreatitis, diverticulitis, Crohn's disease, ulcerative colitis, or other condition that weakens the immune system.

If fever, bloody stools, or diarrhea is persistent for longer than two weeks, a physician may consider blood and stool tests to determine the source of the symptoms.

If the patient develops symptoms suggestive of typhoid fever the GP (general practitioner) will ask the patient whether he/she has done any traveling abroad recently, as well as any contact with people who may be infected. A blood, stool, and/or urine test can help in the diagnosis. However, these tests do not always detect the presence of S. tyhpi bacteria, so the patient may have to undergo some additional tests. A bone marrow sample can more accurately detect the bacteria, but this is time consuming and painful, and is only done if other tests have presented no conclusive results. Additional tests used to diagnose typhoid fever include enzyme-linked immunosorbent assay (ELISA) and fluorescent antibody test. If typhoid fever is diagnosed the doctor will suggest that family/household members be tested as well.

What are the treatment options for salmonellosis (Salmonella infection)?

Salmonella-induced gastroenteritis treatment

Usually, symptoms will last for about one week and will resolve without any treatment. It is important to monitor the hydration levels of the patient by making sure he/she has an adequate fluid intake. If the doctor suspects the bacteria have entered the bloodstream, or are likely to, he/she may prescribe antibiotics.

Antimotility drugs (to stop diarrhea) generally are discouraged, especially in people with bloody diarrhea or diarrhea complicated by a fever.

Typhoid fever treatment

The Salmonella bacteria that causes typhoid can be killed by antibiotics such as ciprofloxacin or ceftriaxone. However, some strains become resistant to antibiotics after long-term use, and antibiotics have known side-effects.

Additional treatments for typhoid include drinking fluid to prevent dehydration and eating a healthy diet to ensure the absorption of nutrients.

Prevention of Salmonella infection

  • Wash your hands with soap and warm water..

      ..before preparing food ..before eating food ..after going to the toilet ..after changing a baby's diapers (UK/Ireland/Australia: nappies) ..after touching pets and other animals ..after gardening.
  • Don't keep cooked and raw foods next to each other.
  • In the fridge, place raw foods in the shelves below ready-to-eat foods.
  • Thoroughly wash raw fruits and vegetables before eating.
  • Cook food thoroughly, especially meats.
  • Keep all cooking utensils and work surfaces clean.
  • Regularly swap used dish cloths for clean ones.
  • Beware of drinking untreated water from streams, rivers and lakes.
  • Do not keep pet reptiles or amphibians inside the house if there are elderly people, pregnant women, very young children, or somebody with a weakened immune system in the household.
  • Of somebody in your household becomes infected with Salmonella, wash all dirty clothes, bedding, and towels in the washing machine at the hottest setting possible. Thoroughly clean toilet seats, toilet bowls, all handles in the toilet, basins and taps after use with a detergent and hot water, followed by a household disinfectant. 

    Salmonella Video


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