About Shigella

Presented By Marler Clark The nation’s leading law firm representing victims of Shigella and other foodborne illness outbreaks.

Shigella Food Poisoning

What is Shigella and how does it cause food poisoning?

Shigella is a species of enteric bacteria that causes disease in humans and other primates. [16, 20] The disease caused by the ingestion of Shigella bacteria is referred to as shigellosis, which is most typically associated with diarrhea and other gastrointestinal symptoms. [11, 16] “Shigella infection is the third most common cause of bacterial gastroenteritis in the United States, after Salmonella infection and Campylobacter infection and ahead of E. coli O157 infection.” [19]

The global burden of shigellosis has been estimated at 165 million cases per year, of which 163 million are in developing countries. [23] More than one million deaths occur in the developing world yearly due to Shigella infection. [23, 29]  By one estimate, Shigella infections are responsible for 300,000 illnesses and 600 deaths per year in the United States. [25]  By another estimate, each year 450,000 Americans are infected with Shigella, causing 6,200 hospitalizations and 70 deaths. [27]

In general, Shigella is one of the most communicable and severe forms of the bacterial-induced diarrheas. [18] No group of individuals is immune to shigellosis, but certain individuals are at increased risk. [16] Small children acquire Shigella at the highest rate, and [24, 28] persons infected with HIV experience shigellosis much more commonly than other individuals. [4]

Shigella is easily spread person-to-person because of its relatively tiny (compared to other bacteria) infectious dose. [16, 23]  Infection can occur after ingestion of fewer than 100 bacteria. [1, 16, 17]  Another reason Shigella so easily cause infection is because the bacteria thrive in the human intestine and are commonly spread both by person-to-person contact and through the contamination of food. [11, 22, 32]

The Discovery and Naming of Shigella

The several types of Shigella bacteria have been named after the lead workers who discovered each one. [11, 16, 20]  The first bacterium to be discovered, Shigella dysentariae, was named after Kiyoshi Shiga, a Japanese scientist who discovered it in 1896 while investigating a large epidemic of dysentery in Japan. [22, 37] The bacterium was also referred to more generally as the dysentery bacillus (the term “bacillus” referring to a genus of Gram-positive, rod-shaped bacteria of which Shigella is a member). [37]

In a summary published annually, the CDC provides an overview of the classification of various types (species) of Shigella bacteria, as follows:

There are 4 major subgroups of Shigella, designated A, B, C and D, and 44 recognized serotypes. Subgroups A, B, C and D have historically been treated as species: subgroup A for Shigella dysenteriae; subgroup B for Shigella flexneri; subgroup C for Shigella boydii and subgroup D for Shigella sonnei. These subgroups and serotypes are differentiated from one another by their biochemical traits (ability to ferment D-mannitol) and antigenic properties. The most recently recognized serotype belongs to subgroup C (S. boydii). [12]

S. sonnei, also known as Group D Shigella, accounts for over two-thirds of shigellosis in the United States. Shigella flexneri, or group B Shigella, accounts for almost all the rest. [11, 19] More specifically, according to one recent study, “From 1989 to 2002, S. flexneri accounted for 18.4% of Shigella isolates submitted to CDC. [4] From 1973 to 1999, only 49 S. flexneri-associated outbreaks of foodborne disease were reported.” [32] In contrast, in developing countries, S. flexneri is the most predominant cause of shigellosis, but S. dysenteriae type 1 is still a frequent cause of epidemic throughout the developing world. [1, 16, 23, 37]


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