Abstract
A new strain of human influenza A (H1N1) virus originated from Mexico in 2009 and spread to more than 190 countries. WHO declared it a level 6 (highest level) pandemic. Some previously healthy patients who were infected by H1N1 virus experienced rapidly progressive pneumonia leading to acute respiratory distress syndrome (ARDS) and even death. The aim of this study was to describe the radiological features in adult patients with H1N1 influenza pneumonia and to see if there were any predominant radiological features.
Retrospective descriptive study was performed during the epidemic of H1N1 influenza infection from August through November 2009 in two Middle East countries. The study involved 209 adult patients with laboratory confirmed H1N1 influenza virus infection by RT-PCR. Pneumonia was confirmed in 54 patients of them. The CXR (No. 54) and the chest CT images (No. 24) of those 54 patients were enrolled in the study for radiological description.
Mean age of patients was 43.07years, of them 27 patients were males. CXR was diagnostic of pneumonia in 47/54 patients and chest CT was diagnostic of pneumonia in 24/24 patients. GGO (34/47 of CXR and 23/24 of CT) and alveolar consolidation (31/47 of CXR and 16/24 of CT) were the predominant pattern. Chest CT was more sensitive than the CXR in the diagnosis (17/24 for CXR and 24/24 for CT) and in showing the different patterns of opacities (p value was 0.02 for alveolar opacity and was 0.00 for both GGO and nodular opacity). The opacities were mainly bilateral (28/47 of CXR and 17/24 of CT), basal and midzonal in CXR (23/47), and peripheral (23/24) in CT. Most of the cases were not extensive (33/47 of CXR and 18/24 of CT).
The predominant radiological pattern in H1N1 pneumonia is bilateral GGO and alveolar consolidation. In the CXR, the opacities were basal and midzonal while in the chest CT were peripheral and peribronchovascular with diffuse zonal involvement. Chest CT is more sensitive than CXR in diagnosing doubtful cases and in showing different patterns of opacities.