2.2 Definitions
Influenza was diagnosed based on the results of rapid antigen detection test using nasopharyngeal swab or sputum specimen, polymerase chain reaction (PCR) method or clinical diagnosis. Clinical diagnoses were made when those who had contact with confirmed influenza patients revealed typical symptoms compatible with influenza.
Patients with pneumonia were diagnosed based on having new radiographic infiltrate, and were classified as having community-acquired pneumonia (CAP) and nursing and healthcare-associated pneumonia (NHCAP) according to the JRS guidelines 4. The types of pneumonia also were categorized as primary viral pneumonia, secondary bacterial pneumonia, or a mixture of the two based on the judgement of the attending physician. Bacterial causes were identified according to sputum and/or blood culture, urinary antigen test, and other microbiologic investigation.
The influenza season is defined as extending from September to the following August. However, the first season was shorter because we started to record from November 2014.