We described a case of persistent influenza AH1N1 and cytomegalovirus respiratory infection in a patient with chronic interstitial lung disease and multiple bilateral pulmonary opacities. An open lung biopsy revealed diffuse organizing alveolar damage, necrotizing bronchiolitis, necrotizing pneumonia and alveolar hemorrhage, compatible with H1N1 infection as well as usual interstitial pneumonia. Diagnoses of an idiopathic CD4+ T cell lymphocytopenia and immunoglobulin G deficiency were made as an unexpected co-denominator of H1N1 and CMV persistent infection changing our treatment approach.Keywords: Respiratory failure; IPF exacerbation; Persistent CMV respiratory infection; Persistent H1N1 respiratory infection; CD4 T cell idiopathic deficiency Case ReportAMCAL, female, fifty-nine years old Brazilian housewife, with five years history of stable interstitial lung disease and a Medical Research Council (MRC) breathlessness scale grade 1 dyspnea, breathing room air with a SpO 2 of 97% without previous medical treatment that was submitted to an abdominoplasty one month before admission ( Figure 1). She had no rheumatologic symptoms and her Antinuclear Antibody (ANA) was negative.After the surgical procedure she evolved with progressive worsening of dyspnea when a diagnosis of respiratory infection due to Influenza AH1N1 virus was made. Olsetamivir, intravenous methylprednisolone (40 mg/day) and respiratory support (Venturi mask with 50% FiO 2 ) were used for five days and the patient showed improvement that lasted for two days. She began to present a right eye conjunctivitis and respiratory failure refractory to non-invasive ventilation. Then, she was intubated and mechanically ventilated with FiO 2 of 70%, PEEP of 12 cm H 2 O and PaO 2 /FiO 2 of 130. Bronchoalveolar lavage, blood cultures, blood quantitative DNA-PCR for cytomegalovirus (CMV) was collected and broad-spectrum antibiotics including ganciclovir were introduced. Her physical examination at ICU admission showed diffuse fine crackles bilaterally, without other remarkable findings.The initial workup showed leukocytosis (13,870 cells/mm 3 , neutrophils 79% and bands 7%), hemoglobin level of 12.7 g/dL and C-reactive protein of 29 mg/L. The electrocardiogram showed no suggestive signs of ischemia; markers of myocardial necrosis and brain natriuretic peptide were within the normal range. Transthoracic echocardiogram showed normal cardiac function (left ventricular ejection fraction of 74%) with normal estimated systolic pulmonary artery pressure (27 mmHg).The initial chest X-ray is shown in Figure 2. A chest computed tomography (CT) scans revealed diffuse ground glass pattern, multiple nodular opacities, peripheral lung cysts and bronchiolectasis (Figure 3). Quantitative blood PCR for CMV revealed 27,000 virus copies/mL and nasal swab RT-PCR for influenza AH1N1 was positive. Bronchoalveolar lavage cultures were all negative, Herpes virus PCR detection was negative, but PCR for CMV detection was positive. Two blood analyses with an interval of one we...