Salmonella is a genus of bacteria that are a major cause of foodborne illness throughout the world. The bacteria are generally transmitted to humans through consumption of contaminated food of animal origin, mainly meat, poultry, eggs and milk.


The symptoms of Salmonella infection usually appear 12-72 hours after infection, and include fever, abdominal pain, diarrhoea, nausea and sometimes vomiting. The illness usually lasts 4-7 days, and most people recover without treatment. However, in the very young and the elderly, and in cases when the bacteria enter the bloodstream, antibiotherapy may be needed.

Most persons infected with Salmonella develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most persons recover without treatment. However, in some persons, the diarrhea may be so severe that the patient needs to be hospitalized. In these patients, the Salmonella infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness.

Every year, approximately 42,000 cases of salmonellosis are reported in the United States. Because many milder cases are not diagnosed or reported, the actual number of infections may be twenty-nine or more times greater. There are many different kinds of Salmonella bacteria. Salmonella serotype typhimurium and Salmonella serotype enteritidis are the most common in the United States. Salmonellosis is more common in the summer than winter.

Children are the most likely to get salmonellosis. The rate of diagnosed infections in children less than five years old is higher than the rate in all other persons. Young children, the elderly, and the immunocompromised are the most likely to have severe infections. It is estimated that approximately 400 persons die each year with acute salmonellosis.

Salmonella typhi

Salmonella typhi is a gram negative bacterium that causes systemic infections and typhoid fever in humans. This rod-shaped, flagellated organism's sole reservoir is humans. It has caused many deaths in developing countries where sanitation is poor and is spread through contamination of water and undercooked food. Eradication seems highly unlikely due to recent emergence of multi drug resistance strains. Salmonella typhi has undergone evolutionary change and has become resistant to antibiotics.

Salmonella typhi has killed over 600,000 people annually all over the world. It is a deadly bacterial disease that causes typhoid fever and is transmitted through food and water. It has become an epidemic in South Asian countries where sanitation is lacking. S. typhi usually invades the surface of the intestine in humans, but have developed and adapted to grow into the deeper tissues of the spleen, liver, and the bone marrow. Symptoms most characterized by this disease often include a sudden onset of a high fever, a headache, and nausea. Other common symptoms include loss of appetite, diarrhea, and enlargement of the spleen (depending on where it is located).

Salmonella typhi involves colonization of the Reticuloendothelial system. Some individuals who are infected with S. typhi become life-long carriers that serve as the reservoir for these pathogens. S typhi has an endotoxin (which is typical of Gram negative organisms), as well as the Vi antigen, which increases virulence. It also produces a protein called invasin that allows non-phagocytic cells to take up the bacterium and allows it to live intracellularly. Salmonella typhi is a strong pathogen for humans due to its resistance to the innate immune response system.

Recently, strains of MDR (multi-drug resistant) Salmonella have been identified and grouped together in a single haplotype named H58. It has been found that these strains are now resistant to nalidixic acid and have reduced susceptibility to fluoroquinolones. This strain has been recently found in Morocco, which shows that the MDR strain has reached as far as Africa.


Though the global under-five mortality from acute diarrhea has decreased from 4.5 million to 1.8 million annually, acute diarrhea continues to take a huge toll on children's health in developing countries. (WHO 2006) Diarrhea represents a significant burden on the health system, the household, and the nutritional status of children. (Bateman and McGahey 2001) Diarrhea is the second leading killer of children under the age of five, accounting for approximately 15% of under-five child deaths worldwide, or almost two million deaths annually. (WHO 2003)

Although the means to prevent diarrhea through water supply, sanitation, and hygiene have been well documented, each year roughly one and one half billion episodes of acute diarrhea occur among children under the age of five.

Diarrhea may be caused by a temporary problem, like an infection, or a chronic problem, like an intestinal disease. A few of the more common causes of diarrhea are

  • Bacterial infections. Several types of bacteria, consumed through contaminated food or water, can cause diarrhea. Common culprits include Campylobacter, Salmonella, Shigella, and Escherichia coli.
  • Viral infections. Many viruses cause diarrhea, including rotavirus, Norwalk virus, cytomegalovirus, herpes simplex virus, and viral hepatitis.
  • Food intolerances. Some people are unable to digest a component of food, such as lactose, the sugar found in milk.
  • Parasites. Parasites can enter the body through food or water and settle in the digestive system. Parasites that cause diarrhea include Giardia lamblia, Entamoeba histolytica, and Cryptosporidium.
  • Reaction to medicines, such as antibiotics, blood pressure medications, and antacids containing magnesium.
  • Intestinal diseases, like inflammatory bowel disease or celiac disease.
  • Functional bowel disorders, such as irritable bowel syndrome, in which the intestines do not work normally.

References World Health Organization Center for Disease Control and Prevention Microbe Wiki Rehydration Project

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