H1N1 influenza: initial chest radiographic findings in helping predict patient outcome

To retrospectively evaluate whether findings on initial chest radiographs of influenza A (H1N1) patients can help predict clinical outcome.

Institutional review board approval was obtained; informed consent was waived. All adult patients admitted to the emergency department (May to September 2009) with a confirmed diagnosis of H1N1 influenza who underwent frontal chest radiography within 24 hours were included. Radiologic findings were characterized by type and pattern of opacities and zonal distribution. Major adverse outcome measures were mechanical ventilation and death.

Of 179 H1N1 influenza patients, 97 (54%) underwent chest radiography at admission; 39 (40%) of these had abnormal radiologic findings likely related to influenza infection and five (13%) of these 39 had adverse outcomes. Fifty-eight (60%) of 97 patients had normal radiographs; two (3%) of these had adverse outcomes (P = .113). Characteristic imaging findings included the following: ground-glass (69%), consolidation (59%), frequently patchy (41%), and nodular (28%) opacities. Bilateral opacities were common (62%), with involvement of multiple lung zones (72%). Findings in four or more zones and bilateral peripheral distribution occurred with significantly higher frequency in patients with adverse outcomes compared with patients with good outcomes (multizonal opacities: 60% vs 6%, P = .01; bilateral peripheral opacities: 60% vs 15%, P = .049).

Extensive involvement of both lungs, evidenced by the presence of multizonal and bilateral peripheral opacities, is associated with adverse prognosis. Initial chest radiography may have significance in helping predict clinical outcome but normal initial radiographs cannot exclude adverse outcome.