Each year, respiratory viruses, including influenza, run rampant throughout the global community. The Centers for Disease Control and Prevention (CDC) estimates that in 2018-2019 alone, more than 40 million people in the United States were infected with influenza, leading to more than 60,000 deaths [1]. In March 2020, Coronavirus disease 2019 (COVID-19) was deemed a global pandemic [2]. Given the distinct differences in transmissibility, clinical course, mortality, and potential treatment options, accurate and early differentiation between diseases such as influenza and COVID-19 is crucial for both patients and clinicians worldwide [3,4].
Patients with influenza and COVID-19 often present with similar symptoms, including cough, sore throat, myalgias, fatigue, fever, and shortness of breath [3]. Thus, differentiating these diseases based on clinical context alone can be challenging. Polymerase chain reaction (PCR) serves as the gold-standard confirmatory testing for both SARS-CoV-2 and influenza infections. However, testing may be inaccessible, time-consuming, and frequently insufficiently sensitive to be used as a rapid screening tool [5,6]. Although computed tomography (CT) imaging can accurately detect pulmonary disease, its role in the pandemic has been inconsistent due to challenges associated with scanner availability, unnecessary radiation exposure, and the potential for exposing additional health care personnel and patients to the virus via this communal imaging resource [7]. Further, transport to a CT scanner ideally requires a degree of clinical stability that some patients with COVID-19 lack.
Point-of-care ultrasound (POCUS) is a bedside diagnostic imaging modality that has become a critical tool for assessing acute dyspnea in the emergency department (ED) [8–10]. Well-established POCUS scanning protocols for evaluating dyspnea, such as the bedside lung ultrasound in emergency (BLUE)-protocol, are now primary steps in ED clinical workups [11]. As such, it has been widely demonstrated that emergency physicians can achieve high-quality cardiac and pulmonary images on POCUS to make accurate diagnoses. Lung ultrasound (LUS) demonstrates a higher sensitivity than chest radiography in detecting pulmonary pathologies such as pleural effusion, alveolar consolidation, pneumothorax, and interstitial syndrome [12–16]. Given its value in assessing lung pathology, LUS has evolved as an important tool to evaluate patients with suspected COVID-19 [17–20]. Among other roles, LUS has been broadly explored for its use in the diagnosis, triage, home monitoring, and pre-hospital evaluation of patients with COVID-19 [20–24].
While there has been ample discussion surrounding the use of LUS in both influenza and COVID-19, no study has evaluated whether LUS alone can differentiate between the two respiratory infections in patients presenting to the ED with undifferentiated dyspnea and viral-like illness [25–27]. The goal of this study was to determine whether a scoring system based on specific pathological LUS findings can help blinded physician reviewers differentiate between COVID-19 and influenza.