Infectious colitis


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PubMed Search: Shigella [title] colon

Elliot Weisenberg, M.D.
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Cite this page: Weisenberg E. Shigella. website. Accessed December 3rd, 2022.
Definition / general
  • Disease caused by bacteria of the Shigella genus
  • Shigella species are virulent, invasive, non motile, non capsulated, facultatively anaerobic, gram negative rods
  • There are four groups:
    • S. dysenteriae
    • S. flexneri
    • S. boydii
    • S. sonnei
  • S. dysenteriae causes the most severe illness
  • Causes watery diarrheal illness associated with fever and abdominal pain, with progression to dysentery (severe diarrhea with blood or mucus in stool) in up to 50%
Essential features
  • Shigella species bacilli are highly infective, virulent, invasive, gram negative rods
  • Watery diarrheal illness associated with fever and abdominal pain is common with progression to dysentery (severe diarrhea with blood or mucus in stool) occurring in up to ½ of patients, in rare instances, more commonly in children, elderly, or debilitated patients infection is fatal
  • Shigellosis is very common especially in the developing world
  • Infection usually occurs from ingestion of bacteria and is associated with poor sanitation
  • In the developed world disease most commonly occurs in children especially in day care centers, migrant workers, travelers, and residents of nursing homes and other institutions
    • Infection occurs primarily in the left colon but also the terminal ileum especially over Peyer patches and other lymphoid aggregates and follicles with overlying M cells
  • Shiga toxin released by S. dysenteriae is associated with more severe disease and possibly complicated by hemolytic uremic syndrome
  • Other complications may occur
  • Infection is treated with antibiotics; antidiarrheal medication is contraindicated
  • Antibiotic resistance is a growing problem
  • Shigellosis and related terms are named after Dr. Kiyoshi Shiga, a Japanese physician and microbiologist who discovered the bacterium in 1897 and subsequently made additional contributions to understanding the disease
  • It is a member of the Enterobacteriaceae family and is closely related to and causes similar disease to enteroinvasive E coli
  • An estimated 165,000,000 cases occur worldwide with 60 - 80% in the developing world; up to 1 million die
  • 13,000 to 19,000 cases are reported annually in the United States and from 20,000 to 50,000 cases per year in the United Kingdom, although not all cases are reported
  • Shigellosis and Entamoeba histolytica are the most important causes of dysentery worldwide
  • Areas where disease is particularly prevalent include parts of India, Nepal, Bangladesh, Somalia, Egypt, Sub-Saharan Africa, Central and South America
  • Access to clean water, proper sanitation, appropriate food handling, hand washing, proper hand hygiene in the health care setting, fly control, and breast feeding reduce incidence and transmission
  • The bacterium is killed by properly chlorinated water
  • Infection occurs from ingestion of bacteria through fecal contamination of food or water; also possibly person to person transmission including sexual activity, especially among men who have sex with men
  • Developing world:
    • Associated with overcrowding, poor sanitation, fly infestations, and lack of access to clean water
    • Breast feeding with protective antibodies and a presumptive improvement in the microbiome as well as reduced exposure to contaminated food and water has been shown to reduce the incidence of disease in infants
    • S. dysenteriae with its associated more severe disease is more common in the developing world
      Developed world:
    • Most commonly occurs in children, especially in day care centers and preschools, migrant workers, travelers, and residents of nursing homes and other institutions
    • S. sonnei is the most common isolate
    • Outbreaks have occurred on cruise ships and also been sourced to contaminated wells
    • Disease is uncommon in children under 6 months of age
    • During outbreaks, secondary cases are common
  • Disease is more common during the summer
  • Shigellosis has been common in military campaigns at least since the Peloponnesian war; in that campaign, the American Civil War and others, shigellosis is believed to have caused more deaths than battle injuries
  • Disease occurs primarily in the left colon and involvement of the terminal ileum is common
  • Disease may occur in other parts of the large bowel
  • Very rarely, fulminant disease occurs because of massive small intestinal invasion (Ikari syndrome)
Pathophysiology / etiology
  • Humans and higher order primates are the only known reservoir
  • Ingested microorganisms are resistant to gastric acid and pass to the intestines, where they are taken up by M cells that overly lymphoid tissue
  • They carry virulence plasmids that encode genes for invasion via a complicated secretion system that allows bacterial proteins to be secreted into host cytoplasm
  • Microorganisms proliferate intracellularly and escape into the lamina propria
  • They are phagocytosed by macrophages which subsequently undergo apoptosis and produce an inflammatory response
  • Microorganisms are released into the lumen and are allowed access to the baso-lateral membrane of colonocytes where they invade
  • Intracellular bacteria multiply and move from cell to cell
  • Bacterial proteins, including toxins are secreted into mucosal cells
  • Disease is generally confined to the mucosa with symptoms caused by destructive inflammation and hemorrhage
  • S. dysenteriae often contains Shiga toxin which (a) inhibits eukaryotic protein synthesis, (b) is associated with watery small bowel diarrhea early in disease and with more severe illness, (c) is associated with hemolytic uremic syndrome
Clinical features
  • Where endemic, it causes 10% of pediatric diarrheal illness and up to 75% of diarrheal deaths, mostly in children under 5
  • Humans and higher order primates are the only known reservoir
  • Different regions have different isolation patterns; e.g. S. flexneri is common in the Philippines
  • Without treatment:
    • Clinical illness usually lasts several weeks but may last from one day to one month; chronic disease is rare
    • Patients may shed bacteria for 1 - 4 weeks after acute illness
    • Long term carriage is rare
  • The stool of infected patients may contain as many as 109 bacteria per gram of stool, and very few bacteria (10 - 100) may cause disease
  • The incubation period is up to one week
  • Most patients suffer a self-limited diarrhea associated with fever and abdominal pain
  • Initially the diarrhea is usually watery and associated with constitutional symptoms (pain, malaise, fever)
  • 50% progress to dysentery (severe diarrhea with blood or mucus in stool or tenesmus), more commonly with infants and young children and with S. dysenteriae infection
  • Fractional stools (an increase in the number of stools with smaller volumes) is characteristic
  • Uncommonly, a subacute presentation occurs in adults that consists of several weeks of waxing and waning diarrhea that is clinically similar to ulcerative colitis
  • Disease is shorter but more serious in infants and young children
  • Most cases occur in children under 6, and most fatalities occur in this group, but elderly, malnourished or debilitated patients are also prone to lethal infections
  • Potential complications include severe dehydration, sepsis, perforation and toxic megacolon
  • Obstruction, reactive arthritis, urethritis, and conjunctivitis may occur, especially with HLA-B27
  • Shigellosis should be suspected when acute diarrheal illness occurs with systemic symptoms or toxemia
  • Very rarely fulminant disease occurs because of massive small intestinal invasion (Ikari syndrome)
  • Traditionally, diagnosis was based on stool culture, but cultures may be falsely negative as microorganisms die rapidly in the environment at room temperature and prolonged transit time may affect yield
  • Cultures may be negative at the height of illness, and multiple cultures may be necessary for diagnosis
  • Ideally rectal swabs should be seeded immediately at bedside
  • Recently a sensitive and specific PCR based test that detects Shigella species bacteria and Shiga toxin as well as Campylobacter group, Salmonella species, Vibrio group, Yersinia enterocolitica, Norovirus, Rotavirus, and Aeromonas species has been introduced
Prognostic factors
  • Disease is more severe in infants, young children, the elderly, debilitated patients and malnourished patients
  • S. dysenteriae is associated with more severe disease
  • Antibiotic treatment reduces the length and severity of illness
Case reports
  • Most authorities consider antibiotic treatment to be mandatory as it shortens duration and severity of infection; however resistance is a growing problem
  • Antidiarrheal medication is contraindicated as it delays clearance of microorganisms and prolongs symptoms
  • Currently fluoroquinolone is recommended if susceptibility is unknown
  • Trimethoprim-sulfamethoxazole, cephalosporins, amdinocillin (in Bangledesh), and nalidixic acid have been used
  • Azithromycin is often used in multidrug-resistant cases
  • In infants, young children and those with severe illness, oral hydration, or if very severe, intravenous hydration may be necessary
Gross description
  • Involved mucosa is edematous, hemorrhagic, inflamed, and ulcerated depending on the severity of infection
  • Pseudomembranes may be present
Microscopic (histologic) description
  • Biopsy is rarely performed
  • Initially the picture is that of acute self limited colitis with cryptitis, crypt abscesses and aphthous ulcers similar to Crohn disease
  • With progression / chronicity, is increased mucosal destruction, increased inflammatory cells and architectural destruction mimicking idiopathic inflammatory bowel disease
Microscopic (histologic) images

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Shigellosis cluster

Electron microscopy images

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Invasive Shigella

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S. flexneri

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Bacterial interaction

Differential diagnosis
  • Early in disease, resembles any cause of acute self limited colitis, especially other bacterial infections
  • Clostridium difficile if pseudomembranes are present
  • With progression, idiopathic inflammatory bowel disease
  • Definitive diagnosis is not possible on a morphologic basis
  • Knowledge of culture or PCR testing is necessary for proper diagnosis
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