Almost all patients affected by pandemic H1N1 infections admitted to an ICU because of lung involvement receive empiric antibiotic therapy. However, preliminary clinical data have failed to demonstrate a consistent role of bacterial co-infection suggesting that severe pulmonary damage occurs as a result of viral pneumonia [1, 11] . A recent autopsy study revealed evidence of concurrent bacterial infection in 29% of cases [8] . In 45% of these the pathogen was S. pneumoniae. These findings confirm the results of previous studies of autopsy specimens showing that most deaths attributed to influenza A virus occurred concurrently with bacterial pneumonia [9] . On the other hand, they highlight the importance of treating influenza patients with both empiric antibacterial therapy and antiviral medications. According to our experience we believe that zoonotic infections had to be ruled out. The lack of known contact with animals in an immunocompetent host appears to rule out zoonotic infections, such as Coxiella burnetii. One of the patients had worked near water ponds, which could have been contaminated by animal urine, but he did not have pulmonary hemorrhage so leptospirosis seems unlikely. Without exposure to birds, Chlamydia psittaci is unlikely. Community-acquired pneumonia (Streptococcus pneumoniae, Haemophilus influenzae, S. pyogenes, or Staphylococcus aureus) can cause severe pulmonary disease, especially in patients with antecedent influenza. These pathogens should have responded to the broadspectrum antimicrobial therapy; therefore, they are unlikely to have been the sole cause of illness. Atypical bacterial pathogens such as Legionella pneumophila cause multifocal pneumonia but usually do not cause upper respiratory tract symptoms [1, 2] .