Send Orders for Reprints to reprints@benthamscience.net Current Medical Imaging, хххх, хх, 1-8 1 RESEARCH ARTICLE Utility of Lung Ultrasound in Decision-making to Prioritize Hospital Admission for COVID-19 Patients: A Developing Country Perspective 1 2 3 4 5,* Samy Zaky , Mohamed A. Metwally , Mohamed El Badry , Ali A Hasan , Sherief Abd-Elsalam , 6 1 7 8 Fathiya El-Raey , Alshaimaa Eid , Mohamed Alboraie , Mohamed Elbahnasawy , Atef Wahdan Elrefai9, Alya A. Elnaggar1, Ehab F Moustafa10, Ahmed Abdelaziz6, Amin Abdel Baki11, Gehan Elas12 13 14 15 16 sal , Akram Abdelbary , Ahmad Said Abdalmohsen , Ehab Kamal , Noha Asem , Hamdy 11 13 17 18 19 Ibrahim , Khaled Taema , Wagdy Amin , Fatma M. Kotb , Ahmed Sh. Mohamed , Neamat A Abdelmageed1, Mohamed Elnady20, Hossam Hosny Masoud20, Mohamed Hassany11 and Hala 21 Zaid 1 Hepatogastroenterology and Infectious Diseases, Al-Azhar University, Cairo, Egypt; 2Hepatology, Gastroenterology and Infectious Diseases Department, Benha University, Benha, Egypt; 3Endemic Medicine Department, Faculty of Medicine, Helwan University, Cairo, Egypt; 4Department of Chest Diseases and Tuberculosis, Assiut University Hospital, Assiut, Egypt; 5Tropical Medicine Department, Tanta University, Tanta, Egypt; 6Department of Hepatogastroenterology and Infectious diseases, Al-Azhar University, Damietta, Egypt; 7Department of Internal Medicine, Al-Azhar University, Cairo, Egypt; 8Department of Emergency Medicine and Traumatology Faculty, Tanta University of Medicine, Tanta, Egypt; 9Department of Chest Diseases, Damietta Faculty of Medicine, Al-Azhar, University, Cairo, Egypt; 10Department Tropical Medicine and Gastroenterology, Assiut University; 11Department of Hepatology, National Hepatology and Tropical Medicine Research Institute, Cairo, Egypt; 12Professor of Pulmonology, Ain Shams University, Cairo, Egypt; 13Critical care medicine, Cairo University, Cairo, Egypt; 14Faculty of Medicine-Cairo University, Cairo, Egypt; 15Medical Research Division. National Research Centre, Giza, Egypt; 16Ministry of Health and Population and Faculty of Medicine, Cairo University; 17Director General for chest diseases, MOHP, Cairo, Egypt; 18Lecturer of internal medicine, faculty of medicine for girls, Al-Azhar university, Cairo, Egypt; 19Professor of chest diseases and Bronchscopy, Tanta, university, Tanta, Egypt; 20Professor of pulmonology, Cairo University, Cairo, Egypt; 21Minister of health and population, Cairo, Egypt Abstract: Background and Aims: In the midst of this pandemic, planning the prioritization of hospital admissions for patients affected with COVID-19 should be of prime concern, particularly in healthcare settings with limited resources. Thus, in this study, we aimed to develop a novel approach to triage COVID-19 patients and attempt to prioritize their hospital admission using Lung Ultrasonography (LUS). The efficacy of LUS in triaging suspected COVID-19 patients and assessing the severity of COVID-19 pneumonia was evaluated; the findings were then compared with those obtained by chest computed tomography (CT). ARTICLE HISTORY Received: December 09, 2020 Revised: March 03, 2021 Accepted: March 16, 2021 DOI: 10.2174/1573405617666210506164243 Methods: This multicenter, cross-sectional study comprised 243 COVID-19 patients who presented to the emergency department in 3 major university hospitals in Egypt. LUS was performed by an experienced emergency or chest physician, according to the local protocol of each hospital. Demographic, clinical, and laboratory data were then collected from each patient. Each patient was subjected to chest CT scans and LUS. Results: The mean age of the 243 patients was 46.7 ± 10.4 years. Ground-glass opacity, subpleural consolidation, translobar consolidation, and crazy paving were reported in the chest CT scans of 54.3%, 15.2%, 11.1%, and 8.6% of the patients, respectively. B-line artifacts were observed in 81.1% of the patients (confluent pattern, 18.9%). The LUS findings completely coincided with the CT findings (Kappa agreement value, 0.77) in 197 patients (81.1%) and offered a diagnostic sensitivity of 74%, diagnostic specificity of 97.9%, positive predictive value of 90.2%, and negative predictive value of 93.6% for the COVID-19 patients. Following the addition of O2 saturation to the lung imaging findings, the ultrasound method was able to demonstrate 100% sensitivity and specificity in accurately differentiating between severe and non-severe lung diseases. Conclusion: LUS with oxygen saturation might prove to be effective in prioritizing the hospital admission of COVID-19 patients, particularly in healthcare settings with limited resources. Keywords: COVID-19, lung, ultrasound, triage, oxygen, pneumonia. *Address correspondence to this author at the Tropical Medicine Department, Tanta University, Tanta, Egypt; Tel: 00201147773440; E-mail: sherif_tropical@yahoo.com 1573-4056/хх $65.00+.00 © хххх Bentham Science Publishers 2 Current Medical Imaging, хххх, Vol. хх, No. хх 1. INTRODUCTION The World Health Organization (WHO) has declared the COVID-19 outbreak as a pandemic on March 11, 2020. Since then, more than 42 million people have contracted the disease, and more than 1.1 million people have died [1]. To date, there is no effective treatment against COVID 19. Moreover, the criteria for the prioritization of hospital admission in these patients have not been set and depend mainly on the severity assessment [2-5]. The imaging features of COVID-19 pneumonia are mainly determined by chest Computed Tomography (CT) for both diagnosis and follow-up [3]. Chest CT scans expose patients to doses of radiation and should be reserved for specific situations, such as the evaluation of mediastinal pathologies; however, these procedures might not be available in triage clinics or designated hospitals, especially in countries with limited resources. Chest Xray (CXR) is considered the standard of care for many diagnostic applications in the intensive care unit (ICU). However, this imaging technique has important methodological limitations and often yields low accuracies [4-9]. The contagiousness of SARS-CoV-2 and the risk of transporting unstable patients with hypoxemia and hemodynamic instability make chest CT a limited option for some patients with COVID-19 [6]. Lung ultrasonography (LUS) has a well-established accuracy for the diagnosis of pulmonary diseases. It is considered safe due to the absence of ionizing radiation; it is costeffective, can be performed at the bedside, and can be easily disinfected. These advantages resulted in the widespread implementation of LUS for the daily assessment and monitoring of COVID-19 patients. Increasing literature and international networks have encouraged the use of LUS for the diagnosis of COVID-19 pneumonia [7, 8]. The results of lung ultrasonography (LUS) are similar to that obtained by high-resolution CT (HR-CT) and superior to those of the standard CXR for the evaluation of pneumonia and acute respiratory distress syndrome (ARDS), with the added advantages of ease of use at the point of care, repeatability, absence of radiation exposure, and low cost [3]. In this current COVID-19 pandemic, LUS is being utilized to triage symptomatic patients for pneumonia in emergency rooms before hospital admission, monitor patients with pneumonia-related lung findings, manage the ventilation and weaning of patients in the ICU and evaluate the effects of antiviral medications [5-15]. In this study, we aim to evaluate the efficacy of LUS in triaging suspected COVID-19 patients and assessing the severity of COVID-19 pneumonia; the findings were compared with those obtained using chest CT. 2. METHODS 2.1. Patients This multicenter cross-sectional study comprised 243 COVID-19 patients who presented at the triage rooms in the Zaky et al. emergency departments located at the Tanta, Al-Azhar, and Assiut university hospitals between June 2020 and August 2020. The patients were selected according to the definition of a suspected case of COVID-19 formulated by the Egyptian Ministry of Health and Population (MOHP) on May 30, 2020 [5]. Adults (>18 years) of both sexes with confirmed COVID-19 infection were included in this study. The clinical features of the patients with suspected COVID-19 infection included fever and/or respiratory symptoms, characteristic images on the chest CT scan, or differential Complete Blood Count (CBC) findings, normal or decreased White Blood Cells (WBCs) with a decreased lymphocytic count. Furthermore, patients who presented with a history of travel to/or residence in communities where cases of COVID-19 were reported within the last 14 days, those who had contact with a viral RNA-positive individual within the last 14 days, or a patient who had a fever or respiratory symptoms or from a community with confirmed COVID-19 cases reported within the last 14 days or with severe acute respiratory infection with no obvious cause were suspected of having contracted COVID-19. COVID-19 infection was confirmed following a laboratory test comprising a Polymerase Chain Reaction (PCR) test using samples obtained from a deep nasal swab (positive nucleic acid of SARS-CoV2) [5, 6]. Patients with a history of chronic interstitial lung diseases, chronic renal failure, or heart failure were excluded from this study. 2.2. Initial Assessment of Suspected COVID-19 Cases Under standard precautions of infection control, the complete medical history of the patient was obtained with particular emphasis on the epidemiological history, clinical assessment, CBC, liver enzymes (Aspartate Transaminase [AST] and Alanine Transaminase [ALT]), kidney function tests (serum creatinine and blood urea), serum ferritin, D-dimer, C-reactive Protein (CRP), and Lactate Dehydrogenase enzyme (LDH). Imaging modalities were performed for all the patients. Emergency LUS was performed by assigned well-trained physicians, according to the local protocol of each participating university hospital, using an ultrasound device (F31; Hitachi Aloka Medical Ltd.); the frequency was set at 3500-5000 MHz for the convex array probe and 7000 MHz for the linear array probe. In addition, a chest CT scan was taken for all the patients enrolled in this study. 2.3. Principles of Emergency LUS The LUS were obtained from the suspected COVID-19 patients in the supine and prone positions to investigate the entire anterolateral and posterior lung surfaces bilaterally. The trans-thoracic scanning window was used to examine the lung and pleura. The intercostal spaces served as scanning windows. The transducer was positioned at right angles to the ribs in order to capture two adjacent ribs, which allowed the lung to slide, reliably identified, and from the anterior rib, artifact could be distinguished. Thus, each intercos- Current Medical Imaging, хххх, Vol. хх, No. хх 3 Role of Lung Ultrasound in Triaging COVID 19 Patients tal space in the upper and lower parts of the anterior, lateral, and posterior regions of the left and right chest wall was carefully examined using these techniques. Ultrasound artifacts arising from the chest wall and pleural surface were used to interpret and diagnose the lung pathologies [6]. The two predominant artifactual patterns include the following: A-lines and B-lines [10]. The A-line is created by an intact “dry” lung parenchyma containing air combined with normal lung sliding. It is strongly suggestive of a normally aerated lung. B-lines are vertical, highly dynamic, hyperechoic artifacts originating from the pleura or consolidation areas of the lungs. More than three B-lines in any single view are considered pathological. B-lines have a variety of patterns, including focal, multifocal, and confluent, and numerous Blines that lie close to each other can become confluent. These lines indicate the accumulation of fluid in the pulmonary interstitial space or alveoli (ground-glass appearance) [11]. Emergency LUS can aid in excluding or confirming the presence of pleural effusion, pulmonary edema/interstitial syndrome, atelectasis, pneumonia, and pneumothorax [12]. The findings of the emergency LUS were compared with those of the chest CT scans (gold standard diagnostic tool of COVID-19 pneumonia). 2.4. Classification of Patients All persons with suspected, probable, or confirmed COVID-19 should be isolated immediately to prevent virus transmission. The patients in this study were classified based on the clinical, laboratory findings, O2 saturation level, and CT findings as follows: mild (individuals with any of the various signs and symptoms of COVID-19, but no shortness of breath, dyspnea, or abnormal chest imaging), moderate (individuals who showed evidence of lower respiratory disease during clinical assessment or imaging with an oxygen saturation [SpO2] of ≥94% on room air at sea level), and severe (individuals with a SpO2 of <94% on room air at sea level, an arterial partial pressure of oxygen to fraction of inspired oxygen ratio [PaO2/FiO2] of <300 mmHg, a respiratory frequency of >30 breaths per minute, or lung infiltrates >50%). Individuals who presented with respiratory failure, septic shock, and/or multiple organ dysfunction were considered to be critically ill. Adherence to infection, prevention, and control measures was applied to protect the patients and healthcare workers. These measures mainly highlighted the use of personal protective equipment and included the thorough cleaning and disinfection of the ultrasound probe along with environmental cleaning and disinfection. 2.5. Statistical Analysis Data were collected and tabulated in an Excel sheet. The SPSS software, version 21, was used for statistical analysis. Continuous data are presented as mean ± the standard deviation. Categorical and ordinal data are presented as numbers and percentages. Comparisons of the demographics and the clinical and laboratory test results among the mild, moderate, and severe patients were made using one-way analysis of variance for continuous variables and the chi-square test for categorical variables. Non-parametric tests were used when indicated. Evaluation of the LUS to diagnose the lung disease was done by calculating the sensitivity, specificity, positive predictive value, and negative predictive value and comparing them with those of the chest CT. The Kappa agreement test was used to evaluate the agreement between the LUS and chest CT findings. A P-value less than or equal to 0.05 was considered significant. Comparisons of the LUS and chest CT findings among the mild, moderate, and severe patients were made using the chi-square test; a post hoc test was used to compare the moderate and severe cases. 3. RESULTS In total, 243 confirmed COVID-19 patients were enrolled in this study. The mean age of the patients was 46.7 ± 10.4 years; the majority of them (72.8%) were males, and 58% were smokers. The demographic and clinical characteristics of the patients in this study are listed in Table 1. Table 2 illustrates the hematological and biochemical data of the patients. Table 1. Comparison between demographic and clinical characteristics of patients upon presentation according to severity. Variables Total (243) Mild (50) Moderate (119) Severe (74) P Gender (Male) Age 177 (72.5%) 43 (86%) 46.7 ± 10.4 46.7 ± 9.8 91 (76.5%) 43 (58%) 0.001 47.7 ± 9.2 45.3 ± 15.5 Days from symptoms onset 4.43± 1.5 0.3 3.27 ± 1.39 4.91 ± 1.43 4.28 ± 1.43 ˂ 0.001 Smoking DM 141(58.1%) 12 (24%) 44 (37%) 46 (62.2) 0.001 98 (40.3%) 12 (24%) 44 (37%) 42 (56.8) 0.001 HTN 77 (31.7%) 13 (26%) 39 (32.8%) 25 (33.8%) 0.6 Cardiac disease 38 (15.6%) 3 (6%) 21 (17.6%) 14 (18.9) 0.1 Fever 130 (53.5%) 18 (36%) 56 (47.1%) 56 (75.7%) ˂ 0.001 Sore throat 70 (28.8%) 13 (26%) 32 (26.9%) 25 (33.8%) 0.5 Cough 132 (54.3%) 18 (36%) 69 (58%) 45 (60.8%) 0.01 Dyspnea 99 (40.7%) 0 (0%) 58 (48.7) 41(55.4%) ˂ 0.001 Anosmia 41 (16.9%) 9 (18%) 21 (17.6%) 11 (14.9%) 0.9 (Table 1) contd.... 4 Current Medical Imaging, хххх, Vol. хх, No. хх Zaky et al. Variables Total (243) Mild (50) Moderate (119) Severe (74) P Diarrhea 43 (17.7%) 6 (12%) 20 (16.8%) 17 (23%) 0.3 Vomiting 37 (15.2%) 6 (12%) 17 (14.3%) 14 (18.9%) 0.5 Smoking, pack/year 8.4± 14.6 2.4 ± 9.2 7.8 ± 14.7 13.4 ± 15.9 0.4 Heart rate 100.2± 19.3 88.9 ± 14.8 98.9 ± 18.8 110.2 ± 15.7 ˂ 0.001 Oxygen saturation 94.4± 4.8 97.2 ± 2.4 96.9 ± 1.7 89.8 ± 2.8 ˂ 0.001 *DM: Diabetes mellitus; HTN: Hypertension. Table 2. Comparison between baseline laboratory values of patients according to severity. Variables Hemoglobin (gm/dl) WBC (1000/cmm) Platelet (1000/cmm) PNL (1000/cmm) Lymphocyte (1000/cmm) INR Blood urea (mg/dl) Serum creatinine (mg/dl) ALT AST LDH Serum ferritin CRP D-dimer Total (243) 13.5 ± 1.7 9,532± 7,303 355.2±136.1 Mild (50) 14.5 ± 1.5 9,203 ± 5,507 311 ± 120 Moderate (119) 13.4 ± 1.8 11,145 ± 5,888 330 ± 107 Severe (74) 13.5 ± 1.5 12,139 ± 5,165 389 ± 156 0.2 0.05 0.01 10,826± 5,304 7,171 ± 6,213 10,986 ± 5,574 10,752 ± 5,065 0.02 1696.6± 926.3 2,096 ± 862 1,754 ± 982 1,629 ± 802 0.08 1.34± 0.52 1.2 ± 0.36 1.3 ± 0.54 1.4 ± 0.53 0.7 75.9 ± 43.1 70.5 ± 37.6 78.7 ± 33.1 74.9 ± 50.5 0.8 1.8 ± 1.1 49.5± 24.5 48.7± 21.3 433.3± 554.9 386.2± 456.7 37.2± 26.7 1251± 966 1.6 ± 0.8 41.6 ± 12.7 36.8 ± 10.9 343 ± 164 296 ± 60 16.7 ± 23.5 660 ± 846 1.6 ± 0.6 50.3 ± 28.2 51.8 ± 23.4 413 ± 162 457 ± 707 41.2 ± 27.4 1323 ± 800 1.9 ± 1.3 50.4 ± 23.1 48.6 ± 20.5 469 ± 618 350 ± 150 40.7 ± 24.4 1,315 ± 1070 0.2 0.4 0.05 0.5 0.3 ˂0.001 0.04 P WBC: White blood cells; INR: International normalized ratio; ALT: Alanine transaminase; AST: Aspartate transaminase; LDH: Lactate dehydrogenase; CRP: C-reactive protein. Table 3. Features of chest ultrasound of the studied patients. + US Chest Findings N (243) % Pleural thickening 41 16.9 B-line artefacts+ 197 81.1 Confluent B line 45 18.9 lung consolidation 21 8.6 Multi lobar distribution of abnormalities 31 12.8 Pleural effusion 8 3.3 Total number of patients showed significant B line by ultrasound either spaced (152) or Coalescent (45). Table 4. Comparison between patients according to severity regarding CT findings. Variables Total (243) Mild (50) Moderate (119) Severe (74) P1* P2** Thickened pleura 13 (5.3%) 0 (0%) 7 (5.9%) 6 (8.1%) 0.1 0.5 Ground glass opacities 132 (54.3%) 0 (0%) 79 (66.4%) 53 (71.6%) ˂ 0.001 0.4 Pulmonary infiltrating shadows 22 (9.1%) 0 (0%) 13 (10.9%) 9 (12.2%) 0.04 0.8 Sub pleural consolidation 37 (15.2%) 0 (0%) 18 (15.1%) 19 (25.7%) ˂ 0.001 0.07 Trans lobar consolidation 27 (11.1%) 0 (0%) 23 (19.3%) 4 (5.4%) ˂ 0.001 0.007 More than 2 lobes infiltration 23 (9.5%) 0 (0%) 17 14.3%) 6 (8.1%) 0.01 0.2 Pleural effusion 7 (2.9%) 0 (0%) 5 (4.2%) 2 (2.7%) 0.3 0.6 Crazy paving 21 (8.6%) 0 (6%) 12 (10.1%) 9 (12.2%) 0.05 0.6 *P1: Comparison among the three groups. **P2: Comparison between moderate and severe patients. Current Medical Imaging, хххх, Vol. хх, No. хх 5 Role of Lung Ultrasound in Triaging COVID 19 Patients Table 5. Comparison between patients according to severity regarding US findings. Variables Mild (50) Moderate (119) Severe (74) P1* P2** Thickened pleural line 3 (6%) 22 (18.5%) 16 (21.6%) 0.06 0.6 B-line 10 (20%) 116 (97.5%) 71 (95.9%) ˂ 0.001 0.5 Small consolidation 0 (0%) 14 (11.8%) 7 (9.5%) 0.04 0.6 Multi lobar distribution 0 (0%) 13 (10.9%) 18 (24.3%) ˂ 0.001 0.01 Pleural effusion 0 (0%) 6(5%) 2 (2.7%) 0.2 0.4 *P1: Comparison among the three groups. **P2: Comparison between moderate and severe patients. Fig. (1). A normal aerated lung (mild case); (1a, b) bright thin, smooth pleural line between two ribs, A lines seen as deeper reputations of the pleural line between the shadow of two ribs and (1c) normal lung sliding. (Sea shore sign using M mode). By ALOKA_US, Hitachi F31, Convex probe. (A higher resolution / colour version of this figure is available in the electronic copy of the article). Fig. (2). LUS of COVID-19 patient, partially de-aerated lung, bilateral peripheral multiple B pattern (2a, b, c), patchy distribution with spared areas (2b) with (2c) or without sub-pleural consolidation (C), a small sub-pleural consolidation and (B) B line. By ALOKA_US, Hitachi F31, Convex probe. (A higher resolution / colour version of this figure is available in the electronic copy of the article). The most frequent features on the chest CT images were ground-glass opacity (GGO; 54.3%) and subpleural consolidation of the lungs (15.2%). Additionally, translobar consolidation and crazy paving were observed in 11.1% and 8.6% of the chest CT images, respectively (Table 3). Interpretation of the chest ultrasound findings revealed the presence of B-line artifacts in 81.5% of the COVID-19 patients; these artifacts demonstrated a confluent pattern in 18.9% of the patients. Pleural thickening and lung consolidation were reported in 16.9% and 8.6% of the patients, respectively (Table 4; Figs. 1 and 2). Chest CT has been considered the gold standard for the diagnosis of COVID-19 pneumonia. Table 5 shows the comparison between the LUS and chest CT findings for the diagnosis of COVID-19 pneumonia. As per our findings, LUS demonstrated a sensitivity of 98.5% (190/193), specificity of 6 Current Medical Imaging, хххх, Vol. хх, No. хх 74% (37/50), a positive predictive value of 93.6% (190/203), and a negative predictive value of 92.5% (37/40) in this study. The LUS findings of 227/243 patients (93.4%) completely coincided with those of the chest CT (Kappa agreement value, 0.77; P ˂ 0.001). Following the addition of O2 saturation to the lung imaging findings, ultrasound demonstrated 100% sensitivity and specificity in accurately differentiating between severe and non-severe lung diseases. All false results in ultrasound compared to CT were in differentiation between mild and moderate disease. The incidence of mild disease was significantly higher among males; furthermore, a lower prevalence of smoking and comorbid disease was noted among the patients with mild disease (Table 1). They presented to the hospital significantly earlier and had higher oxygen saturation levels than patients with moderate and severe disease. Fever, tachycardia, cough, and dyspnea were significantly higher in severe cases (Table 1). Patients with severe disease had significantly higher total leucocyte counts, PMNs, platelet counts, lymphocytic counts, AST, CRP, and D-dimer than those with mild and moderate disease (Table 2). Table 5 shows the comparisons of the chest CT and LUS findings among the mild, moderate, and severe patients. Severe patients presented with a significantly higher prevalence of multilobar distribution in the LUS. 4. DISCUSSION The WHO declared the COVID-19 outbreak as a pandemic with millions of deaths worldwide. The criteria to prioritize the hospital admission of COVID-19 patients, according to the WHO and MOHP protocols, depend on the severity of the disease and the extent of the pulmonary lesions. In this current study, we have developed a novel approach for triaging COVID-19 patients and planning the prioritization for hospital admission using LUS. The aim was to evaluate the efficacy of LUS in triaging suspected COVID-19 patients and assess the severity of COVID-19 pneumonia and compare the findings with those of the chest CT. This approach was intended to meet the needs of low- and middle-income countries, where effective national contingency plans are difficult to develop due to limited resources. Since the COVID-19 outbreak, there is growing evidence regarding CXR and CT findings for diagnosis and assessment of the disease. The role of LUS has not been explored so far, although its usefulness in this pandemic has been suggested in a few case reports [3-9]. The presence of B-lines, an irregular pleural line, and subpleural consolidations are highly suggestive of COVID-19 pneumonia [5]. In addition to its ability to identify subtle lung alterations early in the course of the infection, even in asymptomatic patients, LUS is widely available, can be performed as a rapid bedside test without exposure to ionizing radiation, is cost-effective, and can be repeated to monitor the evolution and extension of pulmonary lesions without any significant risks to the patient [6]. Thus, LUS might help to track the clinical course of the disease, follow up the results of therapy, and change the ven- Zaky et al. tilator settings in severely affected or mechanically ventilated patients [10]. However, the main advantage of trans-thoracic ultrasound (US) in the era of COVID-19 is the reduction in the risk of cross-contamination because it can be done by a single operator; this reduces the exposure of the healthcare worker to SARS-CoV-2 and relieves the shortage of PPE kits experienced in many healthcare facilities [13]. LUS has demonstrated high sensitivity for pulmonary lesions and can overcome the time gap for the transferring of patients to the CT unit [14]. In this current study, 243 COVID-19 patients with different stages of the disease and disease severity were examined; 207 of them (85.2%) were found positive for SARS-CoV-2 at the first nasal swab, and the remaining were deemed positive at the second nasal swab. Fever, cough, and dyspnea were the most common symptoms observed, and most patients with comorbidities presented with moderate to severe disease. These findings were similar to those reported earlier [15]. Some studies have reported that although severe illness can occur in otherwise healthy individuals of any age, it predominantly occurs in adults with advanced age or certain underlying medical comorbidities [16-21]. CRP and D-dimer were found to be significantly higher, and chest CT findings were abnormal in most patients with moderate and severe disease. More than half of the patients had GGO in the chest CT; however, subpleural consolidation, pleural thickening, and crazy paving were observed in a small number of patients only. These findings were in agreement with those generally observed in the era of COVID-19, where CT had a higher sensitivity and showed GGOs in most patients with respiratory symptoms [22], which is the reason why CT had been proposed as the main imaging test and incorporated into different therapeutic and triage strategies since the start of the outbreak [23]. Furthermore, similar to the findings in this current study, TungChen et al. reported the presence of GGOs along with peripheral or diffuse involvement in 72.5% of the patients in their study [24]. Despite the higher sensitivity and major role of CT in the management of patients with COVID-19, it has some notable drawbacks. Radiation exposure and overuse of healthcare resources appear to overshadow the benefits of this method in patients with mild illness. In addition, the lack of availability, difficulty in performing a CT scan in critically ill patients, and exposure to infected patients might outweigh the clinical benefits of using LUS [24]. In this study, chest US showed abnormal findings in most patients with moderate and severe COVID-19. The most common finding in the patients was the presence of B-lines, both discrete (152 patients) and confluent (45 patients). Other findings, such as subpleural consolidation, thickened irregular pleural line, and pleural effusion, were less common. This was consistent with the findings of Peng et al., who identified the typical features of COVID-19 pneumonia on the LUS as follows: thickening of the pleural line with pleural line irregularity; B-lines in a variety of patterns Current Medical Imaging, хххх, Vol. хх, No. хх 7 Role of Lung Ultrasound in Triaging COVID 19 Patients including focal, multifocal, and confluent; consolidations in a variety of patterns including multifocal small, non-translobar, and translobar with occasional mobile air bronchograms; the appearance of A-lines during recovery phase; and pleural effusions are uncommon [25]. Poggiali et al. [26] performed bedside ultrasound on 12 mildly hypoxic COVID-19 patients in their emergency department; they identified a diffuse B-pattern with spared areas in all patients and posterior subpleural consolidations in 3 of them. These findings are similar to those seen in this current study. B-lines are vertical reverberation artifacts on the ultrasound image generated by abnormalities at the lungpleura interface and considered to be the pathognomonic finding of the interstitial syndrome. They are thought to be caused by areas of the partially de-aerated lung or fluidfilled interlobular septae. In the present study, the clinical severity of the patient correlated with the degree of lung involvement on the ultrasound, including the number of Blines. The sensitivity of LUS in diagnosing COVID-19 pneumonia was 97.9%, and the specificity was 74%, as per the findings of this present study. This was in accordance with the findings of a recent study, which reported the presence of radiologic signs that were compatible with COVID-19 on the CT scans and LUS of 72.5% and 78.4% of the patients, respectively; the sensitivity and specificity of LUS for the diagnosis of COVID-19 were close to 100% and 78.6%, respectively [24]. The main limitation of this current study was that LUS, in general, has poor specificity when compared with chest CT because some sonographic findings suggestive of viral pneumonia can be found in other conditions such as pulmonary edema, ARDS, pulmonary fibrosis, and pulmonary contusion. This necessitates using LUS in conjunction with the clinical background of the patient and other confirmatory tests such as PCR. Additionally, operators are in close contact with the suspected cases when performing LUS and might be at increased risk of contracting COVID-19; thus, national and local protocols on the use of PPE kits should be followed. Moreover, performing and interpreting the findings of LUS is highly operator-dependent, and many centers are expected to lack the expertise to implement it as a primary imaging modality. Finally, false-negative ultrasound or CT results might be obtained at the initial stage of the disease, before lung involvement. Consequently, imaging techniques should be considered as a complement to reverse transcriptase (RT)-PCR and laboratory tests. To the best of our knowledge, this is the first study to provide information about a very efficient and simple triaging tool that could be used to prioritize hospital admission for COVID-19 patients in healthcare settings with limited resources. Following the addition of O2 saturation to the lung imaging findings, ultrasound demonstrated 100% sensitivity and specificity in accurately differentiating between severe and non-severe lung diseases. CONCLUSION LUS with O2 saturation was found to be efficient in prioritizing the hospital admission of patients with COVID-19 in healthcare settings with limited resources. The presence of diffuse B patterns with spared areas, with or without subpleural consolidations, in the ultrasound complies with the diagnosis of COVID-19 pneumonia and necessitates hospital admission in confirmed COVID-19 patients. ETHICS APPROVAL AND CONSENT TO PARTICIPATE Approval by the Ministry of Health and Tanta University Faculty of Medicine Ethical Committee: approval number: 33762/06/20. HUMAN AND ANIMAL RIGHTS No animals/humans were used for studies that are the basis of this research. CONSENT FOR PUBLICATION A written consent was taken from each participant in this research. STANDARDS OF REPORTING STROBE guidelines were followed for the study. AVAILABILITY OF DATA AND MATERIALS The authors' institution does not allow public data access. FUNDING None. 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