Data are presented as n or n (%). Clinical criteria were based on respiratory complaints and fever, difficulty in breathing, pulmonary infiltrates compatible with pneumonia, a chest radiograph at admission confirmed by ultrasounds, white blood cell counts >20 G·L⁻¹ or neutrophilis >10 G·L⁻¹ and C-reactive protein level >60 mg·L⁻¹ after 12 h of fever. Undiagnosed nasal aspiration and pleural effusion samples came from different patients, except for one of them. TTMV: torque teno mini virus. TTMV was detected by real-time PCR with primers and probes indicated in table 1. ^#: Isolation and genetic characterisation of TTMV sequences in undiagnosed pleural effusion samples.