Hantavirus infection was verified with the detection of PUUV RNA in plasma (630,000 copies/ml) on the day of admission, while IgM and IgG were negative. Seroconversion with positive IgM and IgG occurred two and seven days later, respectively. Consecutive plasma samples were analysed for PUUV RNA with declining viral copy numbers until negative 16 days post onset of Fig. 1 Chest CT-scans of two European patients with hantavirus pulmonary syndrome. The examination showed pronounced diffuse bilateral interstitial infiltrates with pulmonary oedema, together with bilateral dependent atelectasis and moderate pleural effusions in patient 1 (a) and diffuse bilateral alveolar and interstitial infiltrates with dependent consolidation in patient 2 (b) Fig. 2 Immunohistochemistry results in lung sections from two fatal cases of hantavirus pulmonary syndrome. The findings were condensed oedematous pulmonary parenchyma with alveolar fibrinous exudate and infiltrates of mononuclear cells (a), whereof a vast majority were CD8 + T lymphocytes (b), and many were holding granules containing granzyme B (c) and T cell restricted antigen-1, TIA-1 (d); this immunophenotype is characteristic of activated cytotoxic T lymphocytes. In contrast, CD4 + helper T lymphocytes (e) were uncommon. Viral antigen was detected in capillary vascular endothelium (f) and in mononuclear cells, here represented by a monocyte (f; inset), using Puumala hantavirus nucleocapsid protein monoclonal antibody (A1C5, Progen Biotechnik GmbH, Heidelberg, Germany). For viral antigen, lung samples from two non-hantavirus patients were used as negative controls (data not shown). Panels (Patient 1 in a-e; original magnification, x 400; and Patient 3 in f; original magnification, x 600) display lung sections from paraffin embedded material. Staining was performed using hematoxylin and eosin (a), and immunoperoxidase technique (b-f) disease (data not shown). PUUV RNA was found in bronchoalveolar lavage fluid (11,000 copies/ml) nine days after onset of disease. Bacterial cultures were all negative. The patient remained ventilator-dependent for 13 days, but was finally extubated. She developed critical illness myopathy and needed six weeks in-hospital rehabilitation. At follow-up six months later, she complained of muscle ache during exercise and lowered general fitness, but was steadily improving.