- Reason for surveillance
- Case definitions
- Notification criteria and procedure
- The disease
- Managing single notifications
- Managing special situations
1. Reason for surveillance
- To identify and control cases of disease caused by arboviruses
- To monitor the epidemiology of arboviral diseases and so inform the development of better prevention and control strategies.
2. Case definitions
Both confirmed cases and probable cases should be notified.
A confirmed case requires laboratory definitive evidence only.
A probable cases requires laboratory suggestive evidence only.
Laboratory definitive evidence
- Isolation of Barmah Forest (BF) virus, or
- Detection of Barmah Forest virus by nucleic acid testing, or
- IgG seroconversion or a significant increase in IgG antibody level (e.g. fourfold or greater rise in titre)
Laboratory suggestive evidence
- Detection of Barmah Forest virus IgM and Barmah Forest virus IgG except if Barmah Forest IgG is known to have been detected in a specimen collected greater than 3 months earlier.
3. Notification criteria and procedure
Barmah Forest cases are to be notified by laboratories on diagnosis by routine mail. Probable and confirmed cases should be entered onto NCIMS.
4. The disease
Barmah Forest virus is one of the arboviruses (arthropod borne viruses) known to be pathogenic for humans. The Barmah Forest virus is a member of the genus Alphavirus, in the family Togaviridae (Ross River virus, Sindbis and chikungunya are also alphaviruses).
Mode of transmission
The Barmah Forest virus is transmitted by the bite of an infected mosquito. There is no evidence of direct person-to-person spread. Humans are infectious to mosquitoes for the first few days after the onset of illness. Infected individuals can introduce the virus into receptive areas.
The incubation period is not clear but is likely to be 7 to 10 days.
The severity of Barmah Forest infections are variable and most are asymptomatic. Typical symptoms include rash (particularly on palms), polyarthritis/arthralgia, myalgia, lethargy and low-grade fever. Symptoms such as arthralgia, myalgia and lethargy may occasionally persist for many months.
Ross River and Barmah Forest infections are by far the most commonly observed arboviruses in NSW.
5. Managing single notifications
Within three working days of notification of a confirmed case of a Barmah Forest case acquired in a low/no risk area (including the Sydney metropolitan area) begin follow-up investigation.
Investigation of notifications outside of this is at the discretion of the PHU Director.
Within five working days of notification enter probable and confirmed cases on 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, for Barmah Forest cases acquired in low/no risk areas, 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 the tests be done (encourage the managing doctor to take convalescent sera to confirm the diagnosis)
- Ensure confirmation by a second test if the case has been acquired in a previously unaffected area
- Find out if the case or relevant care-giver has been told what the diagnosis is before interviewing them
- Seek the doctor's permission to contact the case or relevant care-giver
- Review case management
- Identify likely source of infection.
Investigation and treatment
Supportive treatment only.
The case or relevant care-giver should be informed about the nature of the infection and the mode of transmission.
The case or relevant care-giver should be asked to recall if, in the incubation period, he or she had:
- Been bitten by mosquitoes, or
- Visited regions where Barmah Forest virus is endemic, or
- Participated in recreational or other activities involving exposure to bushland or other mosquito habitat (as in, for example, gardening, bushwalking and picnicking).
Isolation and restriction
Clusters of Barmah Forest disease occurring in an atypical geographical area may indicate the need for extraordinary mosquito investigation and control measures and other environmental management strategies and/or health information for the community. This should be discussed with NSW Health Department's Centre for Health Protection.
Identification of contacts
Potentially exposed people are those who may have been exposed to the same source as the case. However, active searching for these people is not usually indicated.
Educate the public living in or travelling to endemic areas to minimise exposure to mosquito bites. Information should indicate geographical location of habitats, and periods of maximum mosquito activity and also refer to protective clothing, appropriate repellents and methods of reducing mosquitoes in the home. Factsheets are available.
6. Managing special situations
Where the case is part of an unusual cluster and where a discrete exposure can be identified, consider an epidemiological investigation and issuing an alert to local residents and visitors.