Salmonella Poisoning

Salmonella Summary
Salmonella bacteria are known to cause salmonellosis, typhoid fever, and paratyphoid fever in humans. Salmonella infection is usually caused by ingesting large amounts of the bacteria in contaminated food or water.
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Salmonella poisoning facts

  • Salmonella are bacteria that cause diseases (gastroenteritis, typhoid fever, paratyphoid fever) in humans.
  • Salmonella are transferred to humans by many routes (for example, unwashed fruits, vegetables and nuts, uncooked or undercooked meats and eggs, contaminated water).
  • Salmonella infections are usually diagnosed by fecal cultures.
  • Antibiotics are often used to eliminate infections in certain populations; many people do not require antibiotics, according to some clinicians.
  • Unique circumstances, such as poor or unsanitary "egg factory" conditions, have caused outbreaks of Salmonella infections and massive contaminated product recalls.
  • Good hygiene practices, washing vegetables and fruits, adequate cooking of meats and eggs, and public health vigilance helps prevent Salmonella infections.
  • Salmonella vaccines are available for poultry and animals; only typhoid fever vaccines are available for humans; there is no vaccine available for salmonellosis.

What is Salmonella?

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Salmonella (S.) is the genus name for a large number (over 2,500) of types of bacteria. Each type is distinctly identifiable microbiologically and immunologically by its specific protein coating. The types are otherwise closely related. Salmonella bacteria are rod-shaped, flagellated, Gram stain-negative, and are known to cause disease in humans, animals, and birds (especially poultry) worldwide. The two major diseases caused by Salmonella spp. are gastroenteritis (also termed non-typhoidal salmonellosis or Salmonella poisoning) and typhoid fever (typhoid and paratyphoid fevers) in humans. Infections caused by these bacteria or their toxins are called salmonellosis, a general term. This article will present both the non-typhoidal and typhoidal salmonellosis, which are closely related.

The terminology that identifies the particular protein coats, or serovars, is complex, and what previously were thought to be various species of the genus Salmonella are now thought by many researchers to be serovars of only two species, S. enterica and S. bongori. However, these designations are not always accepted in the scientific literature. Therefore, common serovars that have been named in the past are still used (for example, S. typhi, S. typhimurium, S. paratyphi, S. enteritidis, S. cholerasuis, S. saintpaul). Minor variations in some serovars are termed subspecies and assigned a number. The serovars are identified by the Kauffman-White classification that uses two major types of antigens (somatic O, along with envelope antigens that may mask O antigens, and flagellar or H antigens) to distinguish the over 2,500 types of Salmonella bacteria. Sometimes laboratories or other reporting agencies identify isolates simply as Salmonella spp. (species) and do not identify the serovars. Nomenclature of these closely related bacteria is likely to remain in flux, even in the current literature. For example, a proposed correct taxonomic name for the organism that causes typhoid fever is Salmonella enterica ssp. enterica, serovar typhi. The simplified version is Salmonella typhi.

The impact of Salmonella bacteria in history is substantial. After examining descriptions of his illness and death, investigators suggest that Alexander the Great died from typhoid in 323 BC. The bacteria seem to thrive when sanitary conditions decline, especially in wars. The bacteria were first isolated from pigs by Theobald Smith in 1885. The genus name Salmonella was derived from the last name of D.E. Salmon, who was Smith's director. In 1896, diagnosis of Salmonella spp. infection in humans was accomplished. One of the first recognized outbreaks happened in 1899 when British troops in South Africa were decimated by typhoid. Of those troops, about 13,000 deaths were due to the disease while 8,000 were due to warfare! The first vaccine available in the U.S. was administered to U.S. troops in the early 1900s.

A famous carrier of Salmonella was Mary Mallon, a cook who was found to be the source of several typhoid outbreaks in the U.S. (1906-1907). At the time, the typhoid "carrier" situation (a carrier sheds the pathogen but is not sick) was not widely understood in the early 1900s. She was known as "Typhoid Mary" and was forced to stop being a food handler. After being out of her job and quarantined on an island for about two years, she was set free and was instructed again not to be a food handler. Nevertheless, she changed her name and did become a food handler and eventually caused several other outbreaks of typhoid with resulting deaths. She was quarantined to an island for over 20 years and died in 1938.

In addition, this highly contagious bacterium has been used as a terrorist tool. In1984, salad bars in Oregon were intentionally contaminated with the bacteria. Studies of Salmonella pathogenic mechanisms have given insight to how bacteria cause disease and are ongoing.

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