PIV detection was performed by conventional culture, direct fluorescent antibody tests, and/or reverse transcription polymerase chain reaction (RT-PCR) assay in respiratory samples. PIV upper respiratory tract infection (URTI) was defined as PIV detection in a nasopharyngeal or sputum sample, with URTI symptoms but no new pulmonary infiltrates. LRTD was divided into 3 groups: possible, probable, and proven. Possible LRTD was defined as PIV detection in a nasopharyngeal or sputum sample with new pulmonary infiltrates (but without confirmation of PIV in the lower respiratory tract) with or without LRTD signs or symptoms (eg, cough, wheezing, rales, tachypnea, shortness of breath, dyspnea, or hypoxia). Probable LRTD was defined as PIV detection in a bronchoalveolar lavage (BAL) or lung biopsy sample with LRTD symptoms, with or without pulmonary function decline, and without new pulmonary infiltrates. The definition of proven LRTD was PIV detection in a BAL or biopsy sample with new pulmonary infiltrates with or without LRTD symptoms.
Viral load was determined by quantitative RT-PCR using stored frozen repository samples [13 (link)]. Peak steroid dose was recorded from the period within 2 weeks before PIV infection in patients with URTI. In PIV LRTD cases, peak steroid doses were recorded from within 2 weeks before and after LRTD diagnosis, respectively, and exact steroid dose at 1 month after diagnosis was also collected. Death caused by respiratory failure was defined as any death caused exclusively or predominantly by respiratory failure [14 (link)].