The purpose of the study is to assess the number of severe, laboratory-confirmed influenza in children hospitalized to paediatric intensive care units. Furthermore, the proportion of these children from all children hospitalized to paediatric intensive care units with acute respiratory infections will be established.

Accurate epidemiological data on severe influenza-associated hospitalizations and fatalities in children are lacking in Germany. The purpose of this study is primarily, to assess the number of severe, laboratory-confirmed influenza in children hospitalized to paediatric intensive care units due to suspected acute respiratory infections/ influenza/ influenza-triggered complications and in children developing influenza during paediatric intensive care unit hospitalization, as well as the number of influenza-associated fatalities. In addition we aim at assessing clinical features, severity, risk factors, complications, diagnostic procedures, treatment and outcome of severe, laboratory-confirmed influenza (and other acute respiratory infections) in these children. Another objective is to estimate the proportion of laboratory-confirmed influenza cases in all children hospitalized to paediatric intensive care units with acute respiratory infections and to evaluate the number and proportion of paediatric intensive care unit hospitalizations due to other viral acute respiratory infections. Additional aims are to estimate the (minimum) incidence of severe influenza-associated hospitalizations in Bavarian children and to estimate the (minimum) incidences of other acute respiratory infections.

Ideally, this study will be conducted between October 2010 and March 2012 in all Bavarian (Germany) hospitals with paediatric intensive care units or paediatric intensive care beds (neonatology excluded). To optimize reporting there will be one study physician at each site responsible for documentation, diagnostic procedures and queries. The local study physician will receive an initiation visit at the start of each season, and will be contacted by the study coordination (situated at the University Children's Hospital in Wuerzburg) bi-weekly by phone. This local study physician summarizes the paediatric intensive care unit admittance in a log sheet, documents epidemiological, demographical, and clinical data in a questionnaire for all suspected acute respiratory infections/influenza patients with parental informed consent (pseudonymous data only), and draws a nasopharyngeal swab or -wash if indicated as routine procedure. A sample will be sent to the central laboratory (Institute for Virology and Immunobiology, University of Wuerzburg) for analysis (influenza-polymerase chain reaction, influenza virus subtyping, other viral acute respiratory infections (respiratory syncytial virus, parainfluenza 1-4, humane metapneumovirus, adenoviruses, rhinoviruses, enteroviruses). The central laboratory will analyse the samples timely and report the results to the respective study site. Additional influenza-tests may also be performed by the local laboratory, at the discretion of the hospitals. All tests, locally and performed in Wuerzburg, and their outcome should be reported in the questionnaire.

Inclusion Criteria:

• Male or female subjects, ≤16 years of age at the time of paediatric intensive care unit admittance. A subject will become ineligible on his/her 17th birthday
• All patients for whom a written Informed Consent Form for study participation can be obtained
• Children presenting with suspected acute respiratory infection of the upper or lower respiratory tract, with acute respiratory infection-related symptoms, e.g. sore throat (in children ≥ 3 years old), coryza (runny nose), cough etc. or B) Children already admitted to the paediatric intensive care unit without apparent acute respiratory infection/influenza-related symptoms that develop acute respiratory infection/influenza-related symptoms within the paediatric intensive care unit or
• Children admitted to the paediatric intensive care unit with suspected influenza (even without respiratory symptoms, e.g. with neurological symptoms) or
• Children admitted to the paediatric intensive care unit with potential influenza-triggered complications and laboratory-confirmed influenza ≤14 days before paediatric intensive care unit admission (by polymerase chain reaction or other influenza test methods)
• Additionally, all children with confirmed / suspected acute respiratory infection/ influenza that died already during admission to the paediatric hospital/ the paediatric intensive care unit will be included (a pseudonymous autopsy report including laboratory analyses (if available) will be requested for these patients).

Exclusion Criteria:

none

Children ≤16 years of age, in hospitals with paediatric intensive care units or paediatric intensive care beds in Bavaria, Germany