Swine-origin influenza a (H1N1) viral infection in children: initial chest radiographic findings.

PURPOSE: To evaluate initial chest radiographic findings of swine-origin influenza A (S-OIV) (also known as H1N1) viral infection in children.
MATERIALS AND METHODS: This was an institutional review board-approved, HIPAA-compliant retrospective study of 108 patients who had microbiologically confirmed S-OIV infection and available initial chest radiographs obtained between April 2009 and October 2009. The final study group was divided on the basis of clinical course (group 1, outpatients without hospitalization [n = 72]; group 2, inpatients with brief hospitalization [n = 22]; group 3, inpatients with intensive care unit admission [n = 14]). Two pediatric radiologists blinded to patient group and lung parenchymal, airway, pleural, hilar, and mediastinal abnormalities systematically reviewed initial chest radiographs. Lung parenchyma and airways were evaluated for pattern (peribronchial markings, consolidation, and ground-glass, nodular, and reticular opacity), distribution, and extent of abnormalities. Radiographs were assessed for presence of pleural effusions or lymphadenopathy. Medical records were reviewed for underlying medical conditions and patient outcomes. Association between frequency of underlying medical conditions and clinical course of S-OIV infection among study groups was evaluated with the Pearson chi(2) test.
RESULTS: The frequency of normal chest radiographs was significantly higher in group 1 (n = 48) than in groups 2 (n = 1) and 3 (n = 0) (P < .001, Pearson chi(2) test). Among patients with abnormal radiographs, the most common finding in group 1 was prominent peribronchial markings with hyperinflation (n = 17), whereas the most common findings in groups 2 (n = 12) and 3 (n = 12) were bilateral, symmetric, and multifocal areas of consolidation, often associated with ground-glass opacities. Nodular opacities, reticular opacities, pleural effusion, or lymphadenopathy were not observed in any patient. An increased frequency of underlying medical conditions was observed in patients with greater severity of illness due to S-OIV infection (group 3, 71%; group 2, 59%; group 1, 31%) (P = .003, Pearson chi(2) test). All 84 patients with available follow-up information have fully recuperated from S-OIV infection.
CONCLUSION: Initial chest radiographs in children with a mild and self-limited clinical course of S-OIV infection are often normal, but they may demonstrate prominent peribronchial markings with hyperinflation. Bilateral, symmetric, and multifocal areas of consolidation, often associated with ground-glass opacities, are the predominant radiographic findings in pediatric patients with a more severe clinical course of S-OIV infection. (c) RSNA, 2009.