[Is H1N1 flu different from seasonal flu on initial plain chest films?]

To determine whether there are differences in the findings on the initial plain chest films of patients with H1N1 influenza and those of patients with flu symptoms during the flu season.

All patients underwent plain-film chest radiography in the Emergency Department for flu symptoms; 95 patients had H1N1 influenza confirmed between July 2009 and December 2009 and 95 patients were attended for symptoms of seasonal flu in January 2009. We analyzed the views obtained, the distribution and location of the radiologic findings, and patients' age, sex, and previous disease.

Patients with H1N1 influenza were younger than those with seasonal flu symptoms (mean 40.2 vs 50.9 years; p<0.001) and fewer had prior disease (48 vs. 63; p<0.001). Plain films were acquired with patients in the standing position in 75 patients in the H1N1 group and in 77 in the seasonal flu group; pathological findings were present in nearly 50% of the patients in each group. The most common findings in the H1N1 group were multifocal patchy consolidations (41.2%; p<0.001) and peribronchial-vascular opacities (16.3%), whereas in the seasonal flu group the most common finding was consolidation in a single lobe (43.9%).

We found significant differences between the radiologic findings of patients with H1N1 influenza (severe) and those of patients with symptoms of flu during the flu season: the incidence of multifocal patchy consolidation was greater in H1N1 patients and H1N1 patients were younger.