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Shigellosis

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Reporting Obligations

Confirmed and suspected cases shall be reported to the local Health Unit.

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Epidemiology

Aetiologic Agent

Shigellosis is an acute bacterial disease, also known as bacillary dysentery caused by an anaerobic Gram-negative bacilli in the family Enterobacteriaceae. Four species cause shigellosis: Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei.

The infectious dose for humans is low; as few as 10–100 bacteria have been shown to cause disease.

Clinical Presentation

An acute bacterial disease characterized by watery, loose stools, fever, nausea and vomiting in mild cases. Sometimes, toxaemia, abdominal cramps and tenesmus with mucoid stools with or without blood in more severe cases. Illness is usually self-limiting, lasting an average of 4–7 days. Severity and case-fatality vary with the age of the host and the serotype of Shigella.

Modes of Transmission

Primary mode of transmission is fecal-oral. Transmission occurs through person-to-person contact, contact with contaminated inanimate objects, ingestion of contaminated food or water and through sexual contact. Primary mode of transmission is fecal-oral. Transmission occurs through person-to-person contact, contact with contaminated inanimate objects, ingestion of contaminated food or water and through sexual contact. Prolonged organism survival in water (up to 6 months) and food (up to 30 days) can occur with Shigella species. Direct transmission is common in children and infected persons who do not thoroughly clean their hands. Risk of transmission increases for individuals engaging in anal-oral sex or in settings where personal hygiene is inadequate, such as in daycare centres. Flies also may be vectors through physical transport of organisms from infected feces to uncovered food items. Foodborne outbreaks of shigellosis associated with an infected food handler have occurred in Ontario.

Incubation Period

Usually 1–3 days but may range from 12–96 hours and up to one week for S. Dysenteriae.

Period of Communicability

During acute infection and until the infectious agent is no longer present in feces, usually within 4 weeks after illness. Secondary attack rates in households can be as high as 40%. Asymptomatic carriers may transmit infection. Appropriate antimicrobial treatment usually reduces duration of carriage to a few days.

Risk Factors/Susceptibility

The elderly, the debilitated and the malnourished of all ages are particularly susceptible to severe disease and death. Two-thirds of cases occur in children younger than 10 years.

  • Men who have sex with men
  • Situations of overcrowding where sanitation is poor, such as jails, institutions for children, daycare centres and mental hospitals
  • Anal-oral contact
  • Consumption of raw/unwashed produce or undercooked shellfish
  • Poor hand hygiene
  • Recreational water contact (sewage contaminated water)
  • History of travel outside province/country

Diagnosis and Laboratory Testing

Isolation of Shigella spp. from an appropriate clinical specimen (e.g., stool, urine).

Enteric culture specimens are accepted only from health units at the Public Health Lab. If you are a clinician, please use a community laboratory to perform your testing. Confirmation and speciation performed at Public Health Lab.

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Treatment and Case Management

Treatment and follow up is under the direction of the attending health care provider.

Provide information to patients on personal prevention measures (careful hand hygiene after defecation, sexual contact and before preparing or eating food). Household members should be assessed for symptoms.

Exclude symptomatic cases who are food handlers, health care providers, caregivers or daycare attendees pending a negative stool sample or rectal swab collected at least 24 hours after cessation of symptoms OR 48 hours after completion of antibiotic therapy.

Patient Information

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Additional Resources

Heymann, D.L. Control of Communicable Disease Manual (19th Ed.). Washington, American Public Health Association, 2008.

References

Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2019.