Last updated:
06 September 2004
1. Reason for surveillance
- To identify the source of clusters and to prevent further cases
- To monitor the epidemiology to inform the development of better prevention strategies.
2. Case definition
Confirmed case
A confirmed case requires laboratory definitive evidence only. Laboratory definitive evidence
Isolation or detection of Shigella species.
Clinical evidence
Not applicable.
Epidemiological evidence
Not applicable. Factors to be considered in case identification
After initial isolation at a local microbiological laboratory, further typing of the organism in NSW is usually performed by the Institute of Clinical Pathology and Medical Research (ICPMR) at Westmead. Serotyping is only required if a cluster is suspected.
3. Notification criteria and procedure
Shigella infection is to be notified by:
- Laboratories on isolation of Shigella (ideal reporting by phone or routine mail).
Only confirmed cases should be entered onto NDD.
4. The disease
Infectious agent
There are 4 serogroups of Shigella: S. dysenteriae (Group A), S. flexneri (Group B), S. boydii (Group C) and S. sonnei (Group D). Serogroups A, B and C are further divided into over 30 serotypes. Mode of transmission
Shigella infection is transmitted by the faecal oral route. The infectious dose may be very low (10-100 organisms). Failing to wash hands adequately after going to the toilet is the primary mode of transmission. Outbreaks have been reported among men who have sex with men in Sydney in 2000 associated with S. sonnei (serotype G). Outbreaks also occur in conditions of crowding and childcare centres. Secondary attack rates in household contacts can be high (40%). Ingestion of contaminated water and improperly handled foods may be a source of infection. Flies may be involved in the transfer of the organism to food. Timeline
The typical incubation period is 1 to 3 days but may be as long as 7 days. Shigellosis is infectious while the organism is present in stools, which may be up to four weeks. Asymptomatic carriers can transmit the infection and although rare, a carrier state can continue for months. Clinical presentation
Shigella infection is characterised by a sudden onset of diarrhoea (containing mucus and/or blood), fever, headache, abdominal pain, nausea and sometimes vomiting. Complications include toxic megacolon, reactive arthritis and rarely, haemolytic uraemic syndrome.
5. Managing notifications
Response Time
Investigation
On same day of notification of a cluster of cases or of a case in a high-risk occupation, begin follow-up of clusters. Cases that do not form part of a cluster are followed up at the discretion of the local Public Health Unit Director unless they are in a high risk occupation (see below). Data entry
Within 3 working days of notification enter confirmed cases on NDD. Within 1 working day of notification of the serogroup of the organism, update NDD. Response procedure
The response to a notification will normally be carried out in collaboration with the case's health carers. But regardless of who does the follow-up, PHU staff should ensure that action has been taken to:
- Confirm the onset date and symptoms of the illness
- Confirm results of relevant pathology tests, or recommend that tests be done
- Find out if the case or relevant care-giver has been told what the diagnosis is before beginning the interview
- Seek the doctor's permission to contact the case or relevant care-giver
- Review case and contact management
- Identify whether the case is in a high-risk occupation (such as a food handler or childcare attendant).
Case management
Investigation and treatment
Refer to Therapeutic Guidelines: Antibiotic. For uncomplicated cases, treatment may be supportive only. Antibiotics may shorten the duration and severity of illness. Multi-drug resistance is common. If the serotyping indicates the case is part of a cluster and beyond a single AHS, investigate in collaboration with the Communicable Diseases Branch. Education
The case or relevant caregiver should be informed about the nature of the infection and the mode of transmission. Emphasise the importance of hand washing in food handling, after going to the toilet and after sexual activity. Isolation and restriction
- Cases who are foodhandlers or care for patients, children or the elderly and who have been unwell with a diarrhoeal illness, should not attend work until 48 hours have elapsed after symptoms resolve. Once symptoms have resolved, the case's hygiene should be assessed by PHU staff for suitability to return to work
- Cases among other workers should not attend work while diarrhoea is present
- Institutional cases should be cohorted (separated from non-infected residents) if possible
- Children in child care should be excluded for 24 hours after diarrhoea ceases. It is not necessary for them to be excluded if they do not have diarrhoea but have a positive stool sample.
Environmental evaluation
Where a common food source of infection is suspected on epidemiological grounds, contact the NSW Food Authority to assess and correct food handling procedures and arrange tracing and collection and testing of suspected source foods. Where drinking water is the suspected source, contact the NSW Health Water Unit. Contact management
Identification of contacts
Persons at risk of infection are those exposed to an infective source. They include household members, sexual contacts (particular relevant to clusters involving men who have sex with men), carers of the case and others who may have consumed any implicated food or water. Treatment
Close contacts should be advised to seek medical attention and submit a stool sample for laboratory testing should symptoms develop.
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