Shigella
Recent Outbreaks
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Subway Restaurant Shigella Outbreak, Lombard, IL 2010
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An outbreak of shigellosis in Lomabard, IL has been traced to a local Subway restaurant.… Continued
- Consumer Resources
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Shigella Consumer Resources… Continued
Related Blog Entries
- Chicago Area Subway Serves Shigella
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The DuPage County Health Department is investigating the cause of food-related illnesses traced to a Subway restaurant in Lombard. A cluster of gastrointestinal illnesses has been …Read more...
- Allegheny County Health Department Warns of Shigella Outbreak
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The Allegheny County Health Department today reported that a growing number of county residents are being diagnosed with a diarrheal illness known as shigellosis. A news …Read more...
Shigella is a family of bacteria that can cause sudden and severe diarrhea (gastroenteritis) in humans. Shigellosis – the illness caused by the ingestion of Shigella bacteria – is also known as bacillary dysentery. It can occur after ingestion of fewer than 100 bacteria (American Public Health Association [APHA], 2000), making Shigella one of the most communicable and severe forms of the bacterial-induced diarrheas (Gomez et al., 2002). Shigella thrives in the human intestine and is commonly spread both through food and by person-to-person contact. It is named after Kiyoshi Shiga, a Japanese scientist who discovered Shigella dysenteriae type 1 in 1896 during a large epidemic of dysentery in Japan (Keusch & Acheson, 1996). Since that time, several types of Shigella bacteria have been discovered – S. dysenteriae, S. flexneri, S. boydii, and S. sonnei – all named after the lead workers who discovered them (Centers for Disease Control and Prevention [CDC], 2009a).
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. In developing countries, S. flexneri is the most predominant cause of shigellosis, but S. dysinteriae type 1 is the most frequent cause of epidemic and endemic disease. No group of individuals is immune to shigellosis, but certain individuals are at increased risk. Small children acquire Shigella at the highest rate. Persons infected with HIV experience shigellosis much more commonly than other individuals, but this may largely be due to an increased risk among men having sex with men (Baer et al., 1999).
The number of shigellosis cases reported annually to the Centers for Disease Control and Prevention (CDC) has varied over the past several years, from more than 17,000 during 1978–2003, to an all-time low of 14,000 in 2004, to almost 20,000 in 2007 (CDC, 2009b). Many cases go undiagnosed and/or unreported, however. The CDC estimates that 450,000 total cases of shigellosis occur in the U.S. every year (Baer et al., 1999; CDC, 2009a). Shigellosis is also characterized by seasonality, with the largest percentage of reported isolates occurring between July and October and the smallest proportion occurring in January, February, and March (Gupta et al., 2004).
Shigella is the third most common pathogen transmitted through food. In FoodNet surveillance areas in 2008, the rate of Shigella was 6.6 per 100,000 population, exceeded only by Salmonella (15.2/100,000) and Campylobacter (12.7/100,000) (CDC, 2009c). During 2006, public health officials reported a total of 1,270 foodborne-related outbreaks from 48 states in the U.S. Although Shigella was responsible for only 10 (1%) of those outbreaks, 183 confirmed cases of shigellosis were reported (CDC, 2009d). This contrasts with an average of 659 cases annually in the previous five years. Shigella is also responsible for a substantial portion of foodborne outbreaks on cruise ships. In a review of cruise ship outbreaks world-wide over several years, 16% of outbreaks were attributed to Shigella, affecting over 2,000 passengers (Rooney et al., 2004). Sanitation violations related to food handling and communicable disease have decreased substantially, however, over the past 15 years (Cramer et al., 2008).
How is Shigella transmitted?
Shigella bacteria are present in the stools of infected persons while they are sick and for up to a week or two afterwards (CDC, 2009a). Most Shigella infections are passed through the fecal-oral route. This happens when basic hygiene and handwashing habits are inadequate and can happen during certain types of sexual activity. It is particularly likely to occur among toddlers who are not fully toilet-trained. Family members and playmates of such children are at high risk of becoming infected.
Shigella infections also may be acquired from eating contaminated food, although contaminated food usually looks and smells normal. Food may become contaminated by infected food handlers who don’t wash their hands with soap after using the bathroom. Vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected feces and then contaminate food. Water may become contaminated with Shigella bacteria if sewage goes into it or if someone with shigellosis swims in or plays with the water (especially in splash tables, untreated wading pools, or shallow play fountains used by daycare centers). Shigella infections can then be acquired by drinking, swimming in, or playing with the contaminated water. Outbreaks of shigellosis have also occurred among men who have sex with men (Gupta et al., 2004).