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.