Clinical and Radiographic Spectrum of Influenza A (H1N1) Infection and Its Association with Disease Severity

Abstract

Background: Influenza A (H1N1) infection remains an important cause of acute respiratory illness and viral pneumonia, with a wide spectrum of clinical severity ranging from mild disease to respiratory failure. For diagnostic purposes of H1NI, Chest imaging plays a crucial role in assessing pulmonary involvement and may provide valuable prognostic information when combined with clinical findings. Objective: To evaluate the correlation between clinical and imaging findings and a worse clinical outcome in patients with a confirmed diagnosis of H1N1 influenza A virus. Methodology: This multicenter observational study was included 140 patients with RT-PCR-confirmed H1N1 infection were included. All the patients' demographic data, clinical features, comorbidities, laboratory parameters, and imaging findings were recorded. The clinical outcomes were classified into good and worse (hospitalization and/or ICU admission). The statistical analysis included univariate and multivariate logistic regression to identify predictors of worse clinical outcomes. Results: Worse clinical outcomes occurred in 42 patients (30.0%). The worst outcomes showed significantly higher frequencies of dyspnea (47.6% vs. 14.3%), diabetes mellitus (21.4% vs. 5.1%), and hypertension (31.0% vs. 13.3%). Poor outcomes were associated with 40.0% of patients with abnormal chest x-rays, whereas only 10.4% of patients with good outcomes had similar x-rays (p < 0.001). CT scan abnormalities were detected in 87.5% of severe cases, with strong associations of ground-glass opacities, consolidation, and diffuse bilateral lung involvement with disease severity. Conclusion: Infectious influenza A (H1N1) clinical features and chest imaging, especially shortness of breath, associated diseases, and large radiographic or CT changes, were the most important factors for the sickness grade.