The present study aimed to evaluate the accuracy of MSCT chest in the detection of COVID-19 cases and to correlate its diagnostic performance with that of the clinical presentation and CBC indices; using RT-PCR assays as a gold standard.

Coronaviruses are non-segmented positive-stranded RNA viruses with a roughly 30 kb genome surrounded by a protein envelope . Two serious coronavirus disease outbreaks have happened in the past two decades: severe acute respiratory syndrome (SARS) in 2003, and Middle East respiratory syndrome (MERS) in 2012 .

Since December 2019, severe acute respiratory syndrome of coronavirus 2 (SARS-CoV-2) has been recognized as the causal factor in a series of severe cases of pneumonia originating in Wuhan, Hubei Province, China . The disease is highly infectious, spreads rapidly worldwide and has been named coronavirus disease 2019 by the World Health Organization that declared the ongoing outbreak as a global pandemic on March 11, 2020.

COVID-19 infection is usually transmitted from human-to-human by close contact. During close contact, people catch the disease by droplet transmission either directly after breathing of contaminated respiratory droplets that were exhaled by an infected person during coughing, sneezing or talking or indirectly by dealing with surfaces and objects used by the infected person. Some aerosol generating medical procedures (i.e., endotracheal intubation, bronchoscopy or disconnecting a patient from the ventilator), may result in easier transmission of such small droplets for greater distances and longer periods of time, in what is known as airborne transmission .

The virus is most contagious during the first three days after onset of symptoms, although the infection may occur up to two days before appearance of symptoms (presymptomatic transmission) and in later stages of the disease. Some people have been infected and recovered without showing symptoms, but uncertainties remain in terms of asymptomatic transmission .

The lungs are the organs most commonly affected by COVID 19 because the virus accesses host cells via the enzyme angiotensin-converting enzyme 2 (ACE2), which is most abundant in type II alveolar cells of the lungs. The density of ACE2 in each tissue correlates with the severity of the disease in that tissue and some have suggested that decreasing ACE2 activity might be protective .The virus uses a special surface glycoprotein called a "spike" (peplomer) to connect to ACE2 and enter the host cell . Though, autopsies of people who died of COVID 19 have found diffuse alveolar damage , and lymphocyte-containing inflammatory infiltrates within the lung .

The clinical presentation is fundamental to identify and isolate suspected COVID-19 cases. Studies have shown that COVID-19 could induce fever, dry cough, dyspnea, and fatigue in infected patients. In more severe cases, the infection can cause viral pneumonia, severe acute respiratory distress syndrome (ARDS) and even death.

Real-time reverse-transcriptase polymerase chain reaction (RT-PCR) is considered the standard diagnostic method of COVID-19 by detection of the viral nucleic acid in the respiratory secretions collected by nasal or oropharyngeal swab. However, high-false-negative rates (FNRs) have been reported with RT-PCR due to multiple intrinsic limitations that includes collection and transportation of samples and diagnostic kit performance. Also, results from quantitative RT-PCR could be affected by variations in viral RNA sequences or in viral loads in the different anatomic sites during the disease natural history . By estimate, the sensitivity of RT-PCR ranges between 60% and 71% . Considering 1014 COVID-19 cases, a recent report found that only 59% of real COVID-19 patients had positive swabs at initial presentation, while chest CT had higher sensitivity in the diagnosis of COVID-19. Chest CT can be helpful in early detection of typical pulmonary abnormalities in case of high suspicion for COVID-19 infection even with initially negative RT-PCR results . Furthermore, CT may be useful in patients follow up and consequently in evaluation of therapeutic efficacy of treatment .

Bilateral multiple peripherally located ground glass opacities (GGO) that commonly involve the posterior segments of the lower lobes with or without sub-segmental patchy consolidations are considered the typical chest CT findings in COVID-19 pneumonia . However, with the growing researches on COVID-19 cases, various other chest CT features was reported including reticular, nodular or crazy paving patterns, air way abnormalities, pleural effusion etc.

Complete blood count (CBC) is one of the laboratory examinations that was recommended by many Chinese reports for early and efficient screening of large number of people for COVID-19 viral infection . Several studies , concluded that during the early stage of infection, the peripheral blood samples revealed normal or slightly reduced lymphocyte, leukocyte and platelet counts. But, with progression of the disease and the appearance of clinical symptoms, most patients were presented with lymphopenia and less commonly thrombocytopenia and leukopenia. Other studies with consistent results, considered lymphopenia, increased neutrophil count and high neutrophil-to-lymphocyte ratio (NLR) as bad prognostic factors that were associated with more frequent development of critical clinical illness, acute respiratory distress syndrome (ARDS) and death.

In absence of treatment or vaccines for COVID-9 it is important to control this rapidly widespread outbreak; hence there is a need for rapid and accurate methods of detection and identification of suspected cases that can be used in the local hospitals and clinics responsible for the diagnosis and management of COVID-19 patients.

Inclusion Criteria:

• patients presented by fever, myalgia or respiratory symptoms
• Close contact with a confirmed COVID-19 patient

Exclusion Criteria:

• pediatric patients
• patients refuse any of the following: MSCT chest, taking of nasopharyngeal swabs or blood sample
• chest MSCT -Angiography was done for suspected vascular complications (e.g., pulmonary embolism)
• severely dyspneic patients with motion artifact on MSCT images.

A prospective single-center cohort study includes all patients ≥18 years of both sex attended to the emergency unit of Assiut University Hospital with a clinical suspicion of COVID-19 infection.