Virological and microbiological tests were performed in bronchioalveolar lavage under sterile conditions. Influenza A H1N1 infection was determined by realtime reverse transcriptase-polymerase chain reaction (RT-PCR) assay. In addition, herpes simplex virus (HSV)-DNA, cytomegalovirus (CMV)-DNA, Epstein-Barr virus (EBV)-DNA, RSV, and adenovirus were tested by TAQMAN PCR. Atypical species, such as Mycoplasma, Pneumocystis jiroveci, or Legionella were screened through PCR. BAL, swabs, and blood cultures were taken routinely on admission and depending on clinical need.