Key messages

  • Shigellosis is a notifiable Group B disease, and school exclusions apply.
  • Shigellosis is characterised by an acute onset of diarrhoea, fever, nausea, vomiting and abdominal cramps.
  • The infectious dose is low and may be as few as 10 organisms.
  • The most important mode of transmission of Shigella is via the faecal–oral route.
  • In Victoria, two or more related cases should be considered indicative of an outbreak and require investigation.

Notification requirement for shigellosis

Shigellosis (Group B disease) must be notified in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary School and children’s services centres exclusion for shigellosis

Exclude until 24 hours after diarrhoea has ceased.

Infectious agent of shigellosis

The genus Shigella consists of four species:

  • Group A – S. dysenteriae
  • Group B – S. flexneri
  • Group C – S. boydii
  • Group D – S. sonnei.

Groups A, B and C are further divided into approximately 40 serotypes, designated by numbers.

Identification of shigellosis

Clinical features

Shigellosis is characterised by an acute onset of diarrhoea, fever, nausea, vomiting and abdominal cramps. Typically, the stools contain blood, mucus and pus, although some people will present with watery diarrhoea. Complications include toxic megacolon and reactive arthritis. Rarely, haemolytic uraemic syndrome can occur. The infectious dose required to produce disease is low and may be as few as 10 organisms.

Illness is usually self-limited and lasts from several days to weeks, with an average of 4–7 days. The severity of infection depends on host factors such as age and nutritional status, as well as the serotype. Infections with S. sonnei usually result in a shorter clinical course and lower case-fatality rate. In contrast, S. dysenteriae is often associated with more serious disease and a higher case-fatality rate.

Asymptomatic infections occur, and carriage may persist for months.

Diagnosis

Diagnosis is made by isolation of Shigella spp. from a clinical specimen.

Incubation period of Shigella

The incubation period depends on the serotype. It varies from 12 hours to 4 days, but is usually 1–7 days.

Public health significance and occurrence of shigellosis

Shigella infection occurs worldwide, but the incidence of specific serotypes varies by country. A recent review of notified cases in Victoria from 2008 to 2013 found that just over half the infections with Shigella were travel related. Indonesia (particularly Bali) and India were the most common destinations. Fifty-two per cent of the infections from Bali were of the S. sonnei group, and the majority remain sensitive to ciprofloxacin. In contrast, returned travellers from India showed a mix of serogroups, with 90 per cent of the isolates showing intermediate or complete resistance to ciprofloxacin. Of the locally acquired infections, half occur among men who have sex with men. Outbreaks have also occurred in childcare centres.

Two-thirds of the cases and most of the deaths worldwide are in children aged less than 10 years. The disease is rare in infants under 6 months of age because breastfeeding is protective.

Secondary attack rates vary, with an increased rate in people with difficulty maintaining personal hygiene (children, people with intellectual disabilities) or people with particular risk factors (men who have sex with men, and food handlers).

Reservoir for Shigella

Humans are the reservoir.

Mode of transmission of Shigella

Faecal–oral transmission is the most important mode of transmission of Shigella. However, infection may be spread via contaminated food, water or milk, or by flies.

Period of communicability of shigellosis

Shigella is communicable during the acute phase and while the infectious agent is present in faeces – usually no longer than 4 weeks. Asymptomatic carriage and excretion may persist for months.

Susceptibility and resistance to shigellosis

Everyone is susceptible to infection, which can follow ingestion of a small number of organisms. In endemic areas, the disease is usually more severe in young children. The risk of infection is increased in men who have sex with men, people with immune deficiency disorders, people attending childcare or having contact with a child in childcare, and international travellers who do not take adequate food and water safety precautions.

Control measures for shigellosis

Preventive measures

Good personal hygiene is the single most important preventive measure. Frequent and thorough handwashing is important before eating and food handling, and after toilet use, especially in young children who may not be completely toilet trained.

Educate travellers on the need for safe food and water consumption.

Control of case

Treatment is usually supportive for mild illness. Antibiotics may shorten the duration and severity of illness; however, their use should be based on the serotype, severity of illness and host characteristics. Current recommendations include antibiotic treatment of asymptomatic carriers only if they fall into a high-risk category (child, food handler, resident of an institution, men who have sex with men, or immunosuppressed). Multidrug resistance is common, particularly for overseas-acquired strains. The choice of antibiotic should be based on the antibiogram of the serotype. Anti-motility drugs are thought to increase the risk of prolonged carriage.

Cases should be educated on the importance of personal hygiene, particularly after using the toilet, and before and after food handling.

Food handlers should be excluded from work until two negative stools have been obtained at least 24 hours apart and not less than 48 hours after completing antibiotics. Cases in institutions should be separated from noninfected residents, if possible.

Control of contacts

The diagnosis should be considered in symptomatic contacts. However, stool cultures may be confined to food handlers and those in situations where the spread of infection is particularly likely (childcare centres, hospitals, institutions).

Symptomatic contacts of shigellosis cases should be excluded from food handling and the care of children or patients until investigated.

Control of environment

Remove contaminated food and water sources. Strict attention should be paid to environmental hygiene in childcare centres, institutions and food premises.

Outbreak measures for shigellosis

Two or more related cases should be considered indicative of an outbreak and require investigation. These cases should be reported immediately to the department. Attempt to determine a common source of infection and identify those at risk of infection.

Refer to Guidelines for the investigation of gastrointestinal illness for further advice and management of outbreaks.

Further information

Lane C, ‘An investigation of relationships between Shigella biotypes with specific antibiotic resistance patterns and the location and mode of transmission by which the cases acquired their infection’, submission for Masters of Public Health, University of Melbourne.

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