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. Polymerase chain reaction (PCR) is a very sensitive testing method for Shigella, although some positives are due to the closely related enteroinvasive Escherichia coli. Consequently diagnoses by PCR alone are categorised as ‘probable’ for national data collection purposes. Culture and antibiotic susceptibility testing is important to guide antibiotic therapy when it is required.

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, although the incidence of specific serotypes varies by country; antimicrobial resistance in Shigella isolates from returned travellers is increasing. Of the locally acquired infections, half occur among men who have sex with men and by 2017 very high rates of antibiotic resistance are being seen in this group, especially in S. sonnei isolates. Outbreaks have also occurred in childcare centres. Notifications of shigellosis in Victoria have increased substantially since 2014.

Worldwide, two-thirds of the cases and most of the deaths are in children aged less than 10 years. The disease is rare in infants under six 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, including during sexual activity. 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.

For both men and women, abstinence from sexual activity with those who currently have or who have recently recovered from diarrhoea of any cause is recommended – this particularly applies to oral-anal contact. 

Control of case

Treatment is usually supportive for mild illness. Anti-motility drugs are thought to increase the risk of prolonged carriage.

Antibiotics may shorten the duration and severity of illness; however, their use should be restricted to certain priority groups due to increasing levels of antimicrobial resistance. Priority groups for antibiotic treatment are cases with severe disease, who are immunocompromised, food handlers, health care workers, childcare workers, children six years or younger and people living or working in residential facilities such as aged care, prisons or disabled group homes. Those with HIV need only be treated if they are known to be immunocompromised with a low CD4 count – the advice of an infectious diseases physician should be sought.

When antibiotics are indicated, choice should be based on the serotype and results of antibiotic susceptibility testing in each instance, considering host factors. Empirical antibiotic treatment is recommended in the above priority groups until sensitivities are known or if diagnosis was by PCR alone, but should be informed by acquisition source. Multi-drug resistance is common, particularly for overseas-acquired strains and in men who have sex with men (MSM). Current Victorian data on antimicrobial resistance in Shigella isolates and recommended empirical antibiotics may be found at: https://www2.health.vic.gov.au/about/publications/researchandreports/antimicrobial-resistance-shigella-isolates-jan-june-2017

In the absence of a suitable empirical oral antibiotic, treatment should be delayed until antimicrobial sensitivities are available for priority cases whose acquisition source is MSM and for whom parenteral antibiotics are not indicated. The advice of an infectious diseases physician should be sought where appropriate.

Current recommendations include antibiotic treatment of asymptomatic carriers only if they fall into a priority group (young child, food handler, health care worker, resident of an institution, or immunosuppressed). 

Cases should be educated on the importance of good hygiene practices, including cleaning of bathroom and kitchen surfaces, handwashing particularly after using the toilet, and before and after food handling. Cases should not prepare food for others until 48 hours after symptoms resolve.

Appropriate safer sex messages are important, especially for MSM. Advise abstinence from all sexual practices while symptomatic and until one week after diarrhoea has resolved. For a further two weeks, reduce faecal-oral exposure by washing hands and preferably genitals with soap and water before and after sexual activity, such as by showering. Barrier methods (condoms, dental dams, latex gloves) are recommended, particularly for sexual practices involving anal contact.

Food handlers, staff of residential facilities, childcare and health care workers should be excluded from work pending individual advice from the department. Cases in institutions should be separated from non-infected residents, if possible. Children must be excluded from primary schools and children’s services until 24 hours has passed since the last loose bowel action.

Control of contacts

The diagnosis should be considered in symptomatic contacts. Particular efforts should be made to trace contacts of those with multi-drug resistant strains to advise them of their exposure, educate about shigellosis and to seek medical advice if symptomatic. Stool cultures may be confined to symptomatic contacts of multi-drug resistant strains, food handlers, healthcare workers and those in situations where the spread of infection is particularly likely (e.g. childcare centres and residential facilities).

Symptomatic contacts of shigellosis cases should be excluded from food handling and the care of children or patients and other priority settings 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 as well as food preparation and bathroom areas in the home.

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, rather than within the 5 days allowed for a single case, as a Group B notifiable disease. 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

Current Victorian data on antimicrobial resistance to assist with empirical prescribing is available at: https://www2.health.vic.gov.au/about/publications/researchandreports/antimicrobial-resistance-shigella-isolates-jan-june-2017

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