Smallpox

World Health Organization (WHO): case definition for notification of smallpox[29]World Health Organization. Smallpox: case definition for notification of smallpox under the IHR (2005). June 2016 [internet publication]. https://www.who.int/publications/m/item/case-definition-for-notification-of-smallpox-under-the-ihr-(2005)

Confirmed case:

• An individual of any age presenting with acute onset of fever (≥38.3°C [≥101°F]), malaise, and severe prostration with headache and backache occurring 2-4 days before rash onset; AND

• Subsequent development of a maculopapular rash starting on the face and forearms, then spreading to the trunk and legs, and evolving within 48 hours to deep-seated, firm/hard, and round well-circumscribed vesicles and later pustules that may become umbilicated or confluent; AND

• Lesions that appear in the same stage of development (i.e., all are vesicles or all are pustules) on any given part of the body (e.g., the face or arm); AND

• No alternative diagnosis explaining the illness; AND

• Laboratory confirmation.

Requires immediate notification to the WHO.

Centers for Disease Control and Prevention: smallpox/variola 2004 case definition[30]Centers for Disease Control and Prevention. Smallpox/variola: 2004 case definition. April 2021 [internet publication]. https://ndc.services.cdc.gov/case-definitions/smallpox-2004

Clinical description:

• An illness with acute onset of fever >38.3°C (>101°F) followed by a rash characterised by firm, deep-seated vesicles or pustules in the same stage of development without other apparent cause.

Laboratory confirmation:

• Polymerase chain reaction (PCR) identification of variola virus DNA in a clinical specimen; OR

• Isolation of smallpox (variola) virus from a clinical specimen (confirmed by variola PCR).

Case classification:

• Confirmed: a case of smallpox that is laboratory-confirmed, or a case that meets the clinical case definition that is epidemiologically linked to a laboratory-confirmed case

• Probable: a case that meets the classical clinical case definition, or a clinically consistent case that does not meet the clinical case definition and has an epidemiological link to a confirmed case of smallpox

• Suspected: a case with a generalised, acute vesicular or pustular rash illness with fever preceding development of rash by 1-4 days

• Exclusion criteria: a case may be excluded as a suspect or probable smallpox case if an alternative diagnosis fully explains the illness or appropriate clinical specimens are negative for laboratory criteria for smallpox.