National case definition: Smallpox

Date of last revision/review: May 2008

National notification

Confirmed, probable and suspect cases of disease should be notified.

Contact the Public Health Agency of Canada immediately using the 24-hour emergency line 1-800-545-7661 even in the event of a suspected case.

Type of surveillance

Routine case-by-case notification to the federal level

Case classification

Confirmed case

Laboratory confirmation of infection:

• isolation of variola virus from an appropriate clinical specimen

  or

• detection of variola virus nucleic acid

Probable case

Clinical evidence of illness in a person who is epidemiologically linked to a laboratory-confirmed case or to a probable case

or

Laboratory evidence of infection:

• negative stain electron microscopic identification of variola virus in an appropriate clinical specimen

Suspect case

Clinical evidence of illness in a person who is not epidemiologically linked to a laboratory-confirmed case or to a probable case of smallpox

or

Atypical lesion known to be associated with the variola virus on a person who is epidemiologically linked to a laboratory-confirmed or probable case

Laboratory Comments

Any testing related to suspected smallpox should be carried out under level 4 containment facilities at NML. 

Contact the Public Health Agency of Canada immediately using the 24-hour emergency line (1-800-545-7661), even in the event of a suspected case, in order to activate the ERAP program.

Clinical evidence

Smallpox is characterized by a febrile prodrome consisting of fever > 38.3° C and systemic symptoms (prostration, headache, back pain, abdominal pain and/or vomiting), which generally lasts one to four days and is followed by the development of a characteristic rash.  The rash consists of deep, firm, well-circumscribed pustules that are mostly all in the same stage of development.  The lesions are characteristically umbilicated.  The lesions initially appear as macules, evolving into papules, vesicles and then pustules in a matter of days.  Finally, crusted scabs form; they then fall off several weeks after the initial appearance of the rash.  Lesions initially appear in the oral mucosa/palate and then progress in a centrifugal pattern to involve the face, arms, legs, palms and soles.  Atypical presentations include flat velvety lesions that do not evolve into pustules and more severe forms with confluent or hemorrhagic lesions.

ICD code(s)

• ICD-10 code(s): B03
• ICD-9 code(s): 050

Type of international reporting

Under the International Health Regulations (IHR) (2005), any event involving one or more cases of smallpox (as defined in WHO case definitions^{Footnote 1}) must be immediately notified to the World Health Organization (WHO), irrespective of the context in which they occur.

• Each State Party shall notify WHO by way of the IHR National Focal Point,^{Footnote 2} and within 24 hours of assessment of public health information, of all events which may constitute a public health emergency of international concern within its territory in accordance with the decision instrument (Annex 2 of the IHR^{Footnote 3}), as well as any health measure implemented in response to those events.
  • According to the algorithm in Annex 2 of the IHR, a case of smallpox is unusual or unexpected and may have serious public health impact and thus shall be notified to WHO.

Comments

It should be noted that the US Centers for Disease Control and Prevention (CDC), Emergency Preparedness and Response, provides slightly different case definitions. The CDC case definitions can be found at Enhanced Surveillance and Case Reporting.

References

Health Canada. Case definitions for diseases under national surveillance. CCDR 2000;26(S3). http://publications.gc.ca/collections/collection_2016/aspc-phac/HP3-1-26-S3-eng.pdf

Communicable Diseases Network Australia. Australian national notifiable diseases case definitions – Smallpox 2004:61. Retrieved July 2017 from http://www.health.gov.au/internet/main/publishing.nsf/Content/cda-surveil-nndss-casedefs-cd_smpox.html

Damon I. Orthopoxviruses: vaccinia (smallpox vaccine), variola (smallpox), monkeypox and cowpox. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 6^th ed. Vol 2. Philadelphia: Churchill Livingstone. Elsevier, 2006.

World Health Organization. International Health Regulations (2005). 3rd ed. Geneva, 2016, from http://www.who.int/ihr/publications/9789241580496/en/