SMALLPOX

Last updated: 06 September 2004

1. Reason for surveillance

• To identify cases and ensure that they are urgently isolated and treated
• To urgently identify and protect contacts at risk of infection.

2. Case definition

Probable Case
A probable case requires either:
Clinical evidence and laboratory suggestive evidence, or
Clinical evidence and epidemiological evidence.

Laboratory suggestive evidence

• Detection of a poxvirus resembling variola virus by electron microscopy
• Isolation of variola virus pending confirmation
• Detection of variola virus by nucleic acid testing pending confirmation.

• Isolation of variola virus, confirmed at the Victorian Infectious Diseases Reference Laboratory, or
• Detection of variola virus by nucleic acid testing, confirmed at the Victorian Infectious Disease Reference Laboratory.

3. Notification criteria and procedure

Smallpox disease is to be notified by:

• Medical practitioners and hospital CEOs on clinical diagnosis (ideal reporting by telephone immediately)
• Laboratories on diagnosis (ideal reporting by telephone immediately)
• Probable and confirmed cases should be entered onto the NDD.

4. The disease

Infectious agent
Variola virus.

Mode of transmission
Smallpox is spread from one person to another through close face-to-face contact, or direct contact with infected bodily fluid or contaminated objects, such as bedding or clothes. Smallpox can also be spread via infected aerosols, by inhaling the organism.
Humans are the only hosts of variola virus. Smallpox is not known to be transmitted by insects or animals.
In normal environmental conditions (ambient temperature, ordinary levels of humidity and exposure to sunlight) the virus is unlikely to survive longer than 48 hours outside of the host.

Time line
The incubation period ranges from 7-17 days, usually 10- 16 days, with a median of 12 days. Cases are infectious for 3 to 4 weeks after onset of fever.

Clinical Presentation
The first symptoms of infection include fever, malaise, headache, and backache (the prodrome phase). These symptoms last from 2 to 4 days. A secondary viraemia begins around day 8 and is associated with the onset of the disease's characteristic fever and rash. The rash begins as macular (flat spots) rash and progresses through vesicular, (spots raised above skin and fluid accumulating inside the spots), pustular (pus-containing skin blister) and crusted (scabs) stages over the following two weeks.
The overall case fatality rate is 30%.

5. Managing single notifications

Response time

Investigation
On notification of any possible case, immediately begin follow-up investigation, and notify Communicable Disease Branch of case details by telephone.

Data entry
Enter probable and confirmed cases on NDD within 1 working day of notification.
Fax completed Smallpox Investigation Form to CDB within 1 working day of notification.

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 the action has been taken to:

• Ensure that the clinical team responsible for the patient is fully compliant with the infection control procedure for smallpox
• Confirm the onset date and symptoms of the illness
• Confirm results of relevant pathology tests, or recommend the tests be done to find out if the case or relevant care-giver has been told what the diagnosis is before interviewing them
• Ensure that all contacts including health workers are identified and receive appropriate post-exposure prophylaxis
• Review case management
• Identify likely source of infection (whether natural or deliberate).