Laboratory-confirmed influenza (including novel influenza subtypes)

Date of last revision/review: May 2008

National notification

Only confirmed cases of disease should be notified.

Type of surveillance

Aggregate weekly influenza detections reporting by the Respiratory Virus Detection Surveillance System (RVDSS)

Case-by-case notification of laboratory-based epidemiologic information by the RVDSS

Enhanced, active reporting of aggregate and case-by-case data by paediatric tertiary care hospitals involved in the Immunization Monitoring Program, Active (IMPACT)

Weekly aggregate reporting of hospitalization, Intensive Care Unit (ICU) admission and death counts by the Provinces and Territories

Case classification

Confirmed case

Clinical illness with laboratory confirmation of infection:

• isolation of influenza virus from an appropriate clinical specimen

or

• demonstration of influenza virus antigen in an appropriate clinical specimen

or

• significant rise (e.g. fourfold or greater) in influenza IgG titre between acute and convalescent sera

or

• detection of influenza RNA

Clinical evidence

Clinical illness defined as influenza-like illness (ILI) is characterized as follows: acute onset of respiratory illness with fever and cough and with one or more of the following:

• sore throat
• arthralgia
• myalgia
• prostration that could be due to influenza virus.

In children under 5, gastrointestinal symptoms may also be present. In patients under 5, or 65 and older, fever may not be prominent. Note: Illness associated with novel influenza viruses may present with other symptoms.

ICD code(s)

ICD-10 code(s)

J10   Influenza due to identified influenza virus

ICD-9/ICD-9CM code(s)

487 Influenza

Type of international reporting

Under the International Health Regulations (IHR) (2005), any event involving one or more cases of human influenza caused by a new subtype (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 human influenza caused by a new subtype is unusual or unexpected and may have serious public health impact and thus shall be notified to WHO.

Comments

In addition to the symptoms of ILI noted above, severe ILI may also include complications such as pneumonia, acute respiratory distress syndrome (ARDS), encephalitis or other severe and life-threatening complications.

References

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

Previous Case Definitions

Case definitions for diseases under national surveillance. CCDR 2000;26(S3).