Clinical case description
Acute febrile respiratory illness (fever >38°C ) with the spectrum of disease from influenza‐like illness to pneumonia.

1. A Confirmed case of swine influenza A(H1N1) virus infection is defined as an individual with laboratory confirmed swine influenza A(H1N1) virus infection by one or more of the following tests*: • real‐time RT‐PCR • viral culture • four‐fold rise in swine influenza A(H1N1) virus specific neutralizing antibodies.

2. A Probable case of swine influenza A(H1N1) virus infection is defined as an individual with an influenza test that is positive for influenza A, but is unsubtypable by reagents used to detect seasonal influenza virus infection OR A individual with a clinically compatible illness or who died of an unexplained acute respiratory illness who is considered to be epidemiologically linked to a probable or confirmed case.

* Note: The test(s) should be performed according to the most currently available guidance on testing (http://www.who.int/csr/disease/swineflu/en/index.html).

Reporting requirements for confirmed and probable cases of swine influenza A(H1N1)

Under the IHR (2005), immediate reporting to WHO is required for human influenza due to a new influenza virus sub‐type. All information will be treated in accordance with the IHR (2005) provisions.

Reports should be sent by the National IHR Focal Point to the relevant WHO IHR Contact Point at the WHO Regional Office, the WHO Country Representative, where applicable, and WHO headquarters in Geneva should be copied on the correspondence (http://www.who.int/csr/alertresponse/ihreventinfo/).

Reporting of individual(s) or clusters under investigation for swine influenza A(H1N1) virus infection

Countries that identify unusual clusters of acute respiratory illness should immediately notify WHO. These consultations will not be reflected in global statistics until their investigation confirms that they are laboratory‐confirmed or probable cases.

Definition of cluster

A cluster is defined as two or more persons presenting with manifestations of unexplained, acute respiratory illness with fever >38°C or who died of an unexplained respiratory illness and that are detected with onset of illness within a period of 14 days and in the same geographical area and/or are epidemiologically linked.

Triggers/signals for the investigation of possible cases of swine influenza A(H1N1)

The primary focus of early investigation is to trigger the initial investigation. Specific triggers include:
• Clusters of cases of unexplained ILI or acute lower respiratory disease

• Severe, unexplained respiratory illness occurring in one or more health care worker(s) who provide care for patients with respiratory disease

• Changes in the epidemiology of mortality associated with the occurrence of ILI or lower respiratory tract illness, an increase in deaths observed from respiratory illness or an increase in the occurrence of severe respiratory disease in previously healthy adults or adolescents

• Persistent changes noted in the treatment response or outcome of severe lower respiratory illness.