Early recognition of the 2009 pandemic influenza A (H1N1) pneumonia by chest ultrasound

Abstract

Introduction: The clinical picture of the pandemic influenza A (H1N1)v ranges from a self-limiting afebrile infection to a rapidly progressive pneumonia. Prompt diagnosis and well-timed treatment are recommended. Chest radiography (CRx) often fails to detect the early interstitial stage. The aim of this study was to evaluate the role of bedside chest ultrasonography (US) in the early management of the 2009 influenza A (H1N1)v infection.

Methods: 98 patients who arrived in the Emergency Department complaining of influenza-like symptoms were enrolled in the study. Patients not displaying symptoms of acute respiratory distress were discharged without further investigations. Among patients with clinical suggestion of a community-acquired pneumonia, cases encountering other diagnoses or comorbidities were excluded from the study. Clinical history, laboratory tests, CRx, and computed tomography (CT) scan, if indicated, contributed to define the diagnosis of pneumonia in the remaining patients. Chest US was performed by an emergency physician, looking for presence of interstitial syndrome, alveolar consolidation, pleural line abnormalities, and pleural effusion, in 34 patients with a final diagnosis of pneumonia, in 16 having normal initial CRx, and in 33 without pneumonia, as controls.

Results: Chest US was carried out without discomfort in all subjects, requiring a relatively short time (9 minutes; range, 7 to 13 minutes). An abnormal US pattern was detected in 32 of 34 patients with pneumonia (94.1%). A prevalent US pattern of interstitial syndrome was depicted in 15 of 16 patients with normal initial CRx, of whom 10 (62.5%) had a final diagnosis of viral (H1N1) pneumonia. Patients with pneumonia and abnormal initial CRx, of whom only four had a final diagnosis of viral (H1N1) pneumonia (22.2%; P<0.05), mainly displayed an US pattern of alveolar consolidation. Finally, a positive US pattern of interstitial syndrome was found in five of 33 controls (15.1%). False negatives were found in two (5.9%) of 34 cases, and false positives, in five (15.1%) of 33 cases, with sensitivity of 94.1%, specificity of 84.8%, positive predictive value of 86.5%, and negative predictive value of 93.3%.

Conclusions: Bedside chest US represents an effective tool for diagnosing pneumonia in the Emergency Department. It can accurately provide early-stage detection of patients with (H1N1)v pneumonia having an initial normal CRx. Its routine integration into their clinical management is proposed.

Figure 1

Study flow-chart. * Routine laboratory tests included white-cell count and chemical analysis (see text). ** Further investigations included H1N1 test, arterial blood analysis and electrocardiogram; in admitted patients diagnostic specimens from lower respiratory tract and blood cultures were recorded; CT scan and repeated chest radiography, if indicated, were also performed. ILI=influenza like illness; SARI=severe acute respiratory illness; CAP=community-acquired pneumonia; CRx=chest radiography; CT=computed tomography; US=ultrasonography.

Figure 2

Chest CT scan shows ill-defined ground-glass opacities with thickened interlobular septa and some peripheral and central ill-defined nodules prevalent at the base in the right lung and diffusely in left lung.

Figure 3

US pattern displaying well distinct multiple B-lines on anterior chest wall longitudinal scan, defining the interstitial syndrome, is shown. Pleural line thickening is evident.

Figure 4

US pattern displaying confluent B-lines (“white lung”) on lateral middle chest wall scanned longitudinally, coexisting with pleural line thickening, is shown.