Severe pulmonary involvement has not been generally perceived to be a significant feature of HFRS. Previously, respiratory symptoms were commonly attributed to fluid overload as a result of renal failure. However, increasing evidence show that lung and heart involvement is common during the acute phase of HFRS [10, 11, 22, 23] . Concerning the cases of European hantavirus infection in our present report, there was only mild or no renal impairment at the time of admission, whereas the respiratory involvement was early and severe, consistent with acute respiratory distress syndrome (ARDS), fulfilling criteria of HPS according to CDC case definition [19] . As described in HPS, the three reported patients suffered from cardiovascular dysfunction, requiring treatment with inotropic and vasopressor drugs [9] . Autopsy results support the cause of death to be cardiopulmonary distress due to hantavirus infection. The lungs of both the deceased patients were oedematous and contained mononuclear cell infiltrates with predominantly CD8 + T lymphocytes, as described in HPS patients [2, 7] . Many cells expressed granzyme B and TIA-1, indicating a cytotoxic activity, which could further be supported by high levels of LDH. We chose to demonstrate the immune response in a non-smoker's lungs (patient 1), but a similar picture was seen in patient 3.