Clinical course and computed tomography abnormalities associated without and with concomitant infection in patients with pandemic influenza A (H1N1) 2009 virus infection

The goal was to evaluate the imaging findings in patients infected primarily with the pandemic influenza A (H1N1) 2009 virus and secondarily with a bacterium. Between October 2009 and March 2010, thirteen patients were included in this study. Five patients had H1N1 pneumonia without evidence of co-infection and their CT images showed diffuse or patchy areas of ground glass opacities and/or consolidations, lower lung zone predominant, without cyst/cavity lesion or newly developing pleural effusion. Another eight patients had H1N1 pneumonia with co-infections. The following organisms were identified: Oxacillin-resistant Staphylococcus aureus (2), Pneumocystis jiroveci (1), Haemophilus parainfluenzae (3), Klebsiella pneumoniae (1), Streptococcus pneumoniae (2), and multiple-drug resistant Acinetobacter baumannii (1). Their CT scans showed diffuse or patchy areas of ground-glass attenuation mixed with consolidation but also revealed cyst/cavity lesions (3), centrilobular nodules (3), tree-in-bud opacity (4), mediastinal lymphadenopathy (6), and pleural effusion (4). These CT changes are definitely different from H1N1 monoinfection. The secondary infectious process may cause additional CT abnormalities. The possibility of H1N1 pneumonia with co-infections should be considered if there are CT findings other than pure H1N1 pneumonia.