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NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

CSTE Position Statement(s)

  • 09-ID-44

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. Influenza-associated deaths in all persons aged <18 years should be reported.

A death should not be reported if:

  1. There is no laboratory confirmation of influenza virus infection.
  2. The influenza illness is followed by full recovery to baseline health status prior to death.
  3. The death occurs in a person 18 years or older.
  4. 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


A death meeting the clinical 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.


*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.

The 2004 case definition appearing on this page was re-published in the 2009 CSTE position statement 09-ID-44. Thus, the 2004 and 2010 versions of the case definition are identical.