Chest imaging findings in hospitalized patients with H1N1 influenza

Previous studies have reported chest radiographic findings of consolidation and ground-glass opacity in patients with swine-origin influenza A (H1N1). However, most of these studies include both hospitalized and outpatients.

To evaluate initial chest radiographic and CT findings of hospitalized swine flu patients, adults and children, confirmed with a real-time reverse transcriptase polymerase chain reaction (PCR) assay for H1N1 virus.

All PCR-verified swine flu patients admitted to the Department of Emergency Medicine (October 1 to December 15, 2009) at Oulu University Hospital, in Northern Finland, who underwent frontal chest radiography within 24 hours of presentation and who were hospitalized, were included. The radiographs and CT scans were assessed for the presence of pneumonia and characterized by pattern and distribution. The patients' medical records were analyzed for demographics, underlying medical conditions, the admission to the intensive care unit (ICU), initiation of mechanical ventilation or non-invasive ventilation support (NIV) and death.

Of 159 H1N1 influenza patients, 135 (85%) underwent chest radiographs at admission; 113 adults and 22 children. Findings of pulmonary infiltrates were detected in 62% (70/113) of adults and 64% (14/22) of children, being bilateral in 67% of adults and 64% of the children. The anatomic location of infiltrates was more often peripheral in adults; 42/70 (60%) vs. 4/14 (29%), P = 0.041, and diffuse among children; 9/14 (64%) vs. 26/70 (37%), P = 0.078. When the ICU and NIV patients were compared to less severe cases, on their chest radiographs four or five lobes were more often affected (65%, 11/17 vs. 34% 23/67, P = 0.029 ). The predominant radiographic findings were consolidation (93% of all patients, 91% of adults and 100% of children) and ground-glass opacity (74% of all, 77% of adults and 57% of children). Pulmonary emboli were detected by CT in 2/9 (22%) patients.

The pandemic 2009 swine influenza causes common and widely distributed infiltrates on chest radiographs among hospitalized patients, which are not peculiar to usual respiratory viral infections, and these findings can not be differentiated from usual bacterial pneumonia.