MSCT Chest in Suspected COVID-19 Patients

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.