Clinical Description

An influenza-associated death is defined for surveillance purposes as a death resulting from a clinically compatible illness that was confirmed to be influenza by an appropriate laboratory or rapid diagnostic test. There should be no period of complete recovery between the illness and death. A death should not be reported as influenza-associa ed if:

• There is no laboratory confirmation of influenza virus infection.
• The influenza illness is followed by full recovery to baseline health status prior to death.
• After review and consultation there is an alternative agreed upon cause of death.

Laboratory Criteria for Diagnosis

Laboratory testing for influenza virus infection may be done on pre- or post-mortem clinical specimens, and include identification of influenza A or B virus infections by a positive result by at least one of the following:
 

• Influenza virus isolation in tissue cell culture from respiratory specimens;
• Reverse-transcriptase polymerase chain reaction (RT-PCR) testing of respiratory specimens;
• Immunofluorescent antibody staining (direct or indirect) of respiratory specimens;
• Rapid influenza diagnostic testing of respiratory specimens;
• Immunohistochemical (IHC) staining for influenza viral antigens in respiratory tract tissue from autopsy specimens;
• Four-fold rise in influenza hemagglutination inhibition (HI) antibody titer in paired acute and
  convalescent sera*.

Case Classification:

Confirmed
A death meeting the clinical case definition that is laboratory confirmed. Laboratory or rapid diagnostic test confirmation is required as part of the case definition; therefore, all reported deaths will be classified as confirmed.
 

Comments
*Serologic testing for influenza is available in a limited number of laboratories, and should only be considered as evidence of recent infection if a four-fold rise in influenza (HI) antibody titer is demonstrated in paired sera. Single serum samples are not interpretable.