- Reason for surveillance
- Case definition
- Notification criteria and procedure
- The disease
- Managing notifications
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
A confirmed case requires laboratory definitive evidence only.
Laboratory definitive evidence
Isolation or detection of Shigella species.
Factors to be considered in case identification
The Enteric Reference Laboratory (ERL) at the Institute of Clinical Pathology and Medical Research (ICPMR), Westmead Hospital can perform further typing of isolates.
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 the Notifiable Conditions Information Management System (NCIMS).
4. The disease
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 contact with faeces is a main contributor to transmission. Outbreaks of infection have been reported among men who have sex with men in Sydney in 2000 and 2009 (S. sonnei (biotype 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.
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.
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
On same day of notification of a cluster of cases or within 3 days for single cases, begin follow-up investigation. Notify the Communicable Diseases Branch of clusters.
Within 3 working days of notification enter confirmed cases on NCIMS.
Within 1 working day of notification of the serogroup of the organism, update NCIMS.
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 results of relevant pathology test
- ensure isolate is sent to ICPMR for serotyping
- seek the doctor's permission to contact the case or relevant care-giver. Find out if the case or relevant care-giver has been told what the diagnosis is prior to contact.
- review case and contact management
- interview the case for likely source of infection (including overseas travel and for males, homosexual contact (and attendance at sex on premises venues).
- for cases with no overseas travel or homosexual contact collect a three day food history.
- determine Aboriginality.
- provide advice on personal hygiene to reduce the likelihood of transmission in households
- identify whether the case is in a high-risk occupation (such as a food handler or childcare attendant)
Within Aboriginal communities, shigellosis can be an important issue, and a single notification should prompt discussion with local Aboriginal Health Workers. In conjunction with local health services and Aboriginal health staff, conduct a risk assessment in regard to the likelihood of ongoing infection in the community and consider enhanced surveillance for early case detection and prevention messages for the community.
Investigation and treatment
Refer to Therapeutic Guidelines: Antibiotic. Although antibiotic therapy may not be necessary to relieve the symptoms of mild shigellosis, it is recommended in all cases for public health reasons as a very low inoculum causes infection. Antibiotics may shorten the duration and severity of illness. Multi-drug resistance is common and therapy may have to be modified according to the results of culture and susceptibility tests.
If the data indicate that the case is part of a cluster and beyond a single Area Health Service, investigate in collaboration with the Communicable Diseases Branch.
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 food handlers 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. The case should be provided with information regarding hand washing and hygiene before returning to work.
Cases among other workers should not attend work while diarrhoea is present.
Institutional cases should be cohorted (separated from non-infected residents and cared for with dedicated staff with dedicated hand washing facilities) if possible.
Exclusion of school children from school until cessation of diarrhoea.
Children in child care should be excluded until diarrhoea has ceased for 24 hours. It is not necessary for them to be excluded if they do not have diarrhoea but have a positive stool sample.
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.