OBJECTIVE: To document the prevalence of respiratory virus infections in patients with chronic cardiac or pulmonary disorders admitted to a critical care unit for acute cardiorespiratory failure. DESIGN, SETTING, PATIENTS: The study took place in a critical care unit during two consecutive winters. All patients admitted to the unit for acute respiratory or cardiac failure were enrolled. A nasal swab was taken for polymerase chain reaction (PCR) detection of influenza virus, respiratory syncytial virus (RSV), metapneumovirus, rhinovirus, and coronavirus. RESULTS: One hundred twenty-two patients were enrolled. Their mean age was 69 years; 42% of the patients were female; the new simplified acute physiology score (SAPS II) score on admission was 35.6; 94% of patients had acute respiratory failure, 14% reported "influenza-like" illness before admission, and 11% of patients died in the unit. Twenty-one patients (17%) tested positive for a respiratory virus. The per-1,000 positivity rates were influenza virus 66, RSV 49, rhinovirus 33, metapneumovirus 16, and coronavirus 8. No link was found between virologic results and clinical outcome. A strong link was found between the rate of influenza virus positivity and the incidence of flu-like illness in the community (p=0.017). CONCLUSION: These results show that respiratory virus infection-particularly influenza virus infection during epidemic periods-is common among patients hospitalized for acute cardiorespiratory failure.