This is a 66-year-old man with a history of pulmonary neoplasia (stage iiiB non-small cell carcinoma) treated with chemotherapy and radiotherapy, who remained free of disease, with subsequent appearance of a brain metastasis on which complete resection was carried out pending the start of holocranial radiotherapy. He came to the emergency department with dyspnoea on minimal exertion for 10 days and fever of up to 39°C. She denied cough and expectoration. There was no epidemiological history of interest. He started antibiotic treatment on an outpatient basis without improvement. On arrival he presented severe respiratory failure requiring high FiO2 and was admitted to the critical care unit of our centre. He presented rapid progression of respiratory failure and at 24h required orotracheal intubation and mechanical ventilation. The initial chest X-ray showed an alveolar infiltrate in the left base with the appearance of bilateral pulmonary infiltrates in subsequent controls. Pulmonary artery catheterisation ruled out heart failure, with pulmonary capillary pressure below 18mmHg, showing signs of moderate pulmonary hypertension. Laboratory tests showed disseminated intravascular coagulation (D-dimer greater than 20,000ng/ml, maximum thrombocytopenia of 47,000/l and maximum prothrombin time of 1.58 ratio), acute renal failure with creatinine levels of up to 2.33mg/dl and elevated lactate dehydrogenase (LDH) with maximum values of 2,305U/l. Antibiotic treatment was started empirically with piperacillin-tazobactam and azithromycin, and corticosteroids were subsequently added. Given the poor evolution, with persistent severe respiratory insufficiency and worsening of the pulmonary infiltrates of an unrelated cause, a thoracic CT scan was performed showing very extensive bilateral parenchymal involvement in ground glass, with a radiological appearance indicating diffuse alveolar damage or an infectious process of atypical characteristics. Bronchoalveolar lavage was performed with negative bacteriological culture, negative Ziehl-Nielsen and negative Pneumocystis jirovecii. Serology for atypical pneumonia (Legionella, Chlamydia, etc.) was requested and was negative. Finally, given the clinical characteristics and in a pandemic situation for the influenza A (H1N1) virus, probable infection by the virus was suspected, a nasal and pharyngeal swab was performed, and the real-time polymerase chain reaction (RT-PCR) was positive, for which treatment with oseltamivir was added. The patient had a good clinical evolution with rapid improvement of the radiological infiltrates, and weaning from ventilation was carried out without incident. The patient was discharged after one month of hospitalisation.

None of the healthcare professionals who attended the patient presented symptoms indicative of influenza in the following days.