Background

In late 2019, a new coronavirus was linked to several cases of pneumonia in the city of
Wuhan, Hubei province, China. On February 11, 2020, the World Health Organization (WHO)
designated COVID-19 a pandemic disease. The mortality associated with COVID-19 patients that
required management in a critical care unit is approximately 4.3%. COVID-19 is caused by
severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Diagnosis of COVID-19 is made
with a positive test (i.e. reverse transcriptase-polymerase chain reaction, RT-PCR) from a
person with clinical signs and symptoms of a respiratory tract infection. Viral pneumonia is
currently a challenge worldwide as it is associated with high morbidity and mortality. In
June of 2009, the WHO declared influenza A H1N1 a pandemic disease. Worldwide, influenza H1N1
had a mortality of 11%, with a higher mortality rate among people older than 50 years of age
(i.e. 18-20%). Influenza diagnosis can be established using RT-PCR. Around 200 million cases
of community-acquired viral pneumonia occur each year worldwide, 100 million in children, and
100 million in adults. Imaging findings in viral pneumonia are diverse and overlap with
findings associated with non-viral infections and inflammatory conditions. However,
identifying the underlying viral pathogens may not always be easy. Several imaging patterns
have been described in association with these viruses. Although a definitive diagnosis cannot
be achieved based on imaging studies, imaging pattern recognition of viral pneumonia can help
differentiate between viral and bacterial pathogens; thus, reducing the use of indiscriminate
antibiotics. There are few studies that correlate tomographic findings in patients with viral
infections in the lower respiratory tract.

The use of computed tomography (CT) should be considered as the first option for diagnostic
imaging in patients with suspected pneumonia. Peripheral multifocal ground glass patterns
with irregular consolidation images found in the lower lobes or posteriorly in pulmonary CT
scans have been described in patients with viral pneumonia due to SARS-CoV-2. Furthermore,
complicating the diagnosis of atypical viral pneumonia, 17.9% of mild COVID-19 and 2.9% of
moderate-severe COVID-19 patients did not have CT evidence of pneumonia upon hospital
admission. One recent study compared the CT radiological patterns found in COVID-19 pneumonia
to other viral pneumonias (i.e. influenza, parainfluenza, adenovirus, and respiratory
syncytial virus) reporting higher peripheral distribution (i.e. 80% vs. 57%, p<0.001), more
ground-glass opacities (i.e. 91% vs 68%, p<0.001), greater frequency of fine reticular
opacities (i.e. 56% vs. 22%, p<0.001), and vascular thickening in COVID-19 patients;
meanwhile, other viral pneumonias were more likely to have a mixed distribution pattern(i.e.
35% vs. 14%, p<0.001), have pleural effusion (i.e. 39% vs. 4.1%, p<0.001), and present
visible lymph nodes (10.2% vs. 2.7%, p<0.001). Another study compared the pulmonary
radiological patterns associated with COVID-19 compared to influenza (A and B) reporting
higher round opacities (i.e. 35% vs. 17%, p=0.048) and greater frequency of interlobular
septal thickening (i.e. 66% vs. 43%, p=0.014) in patients with COVID-19; conversely,
influenza patients had a higher frequency of nodular lesions (i.e. 71% vs. 28%, p<0.001),
higher frequency of small dense nodular lesions (i.e. 40% vs. 9%, p<0.001), and more likely
to have pleural effusion (i.e. 31% vs. 6%, p<0.001).

Research questions

1. What are the pulmonary tomographic findings in patients diagnosed with
community-acquired pneumonia secondary to SARS-CoV-2?

2. What are the pulmonary tomographic findings in patients diagnosed with
community-acquired pneumonia secondary to H1N1 influenza?

3. Are the 28-day survival distributions different for SARS-CoV-2 and H1N1 influenza?

4. Is there a difference in the 28-day survival distribution and the pulmonary tomographic
radiological patterns in patients with pneumonia secondary to SARS-CoV-2?

5. Is there a difference in the 28-day survival distribution and the pulmonary tomographic
radiological patterns in patients with pneumonia secondary to H1N1 influenza?

6. What factors are associated with the survival differences in 28-day mortality in both
groups and between groups?