Introduction
In December 2019, pneumonia for unknown reasons emerged in Wuhan city, Hubei of China. Chinese scientists extracted novel Coronavirus from patients’ specimens and named it as severe acute respiratory syndrome coronavirus 2 on 7 January 2020 that was formerly called N-cov-20191. The World Health Organization (WHO) finally announced the new coronavirus as COVID-19 in February 20201. Coronaviruses are a large family of viruses that are well-known to cause a wide variety of clinical manifestations from the mild common cold to severe forms of respiratory diseases such as Middle East Respiratory Syndrome (MERS) and severe acute respiratory syndrome (SARS) 2,3. The clinical manifestations of COVID-19 vary from asymptomatic infection, mild forms of upper respiratory tract illness, viral pneumonia, acute respiratory failure, and death 4,5. The most common clinical features of COVID-19 including fever, dry cough, fatigue, diarrhea, severe muscle pain, and pneumonia that lead to Acute Respiratory Distress Syndrome (ARDS), metabolic acidosis, septic shock, thrombosis, and heart failure, renal failure, and liver disease 6,7. Although the mild form of COVID-19 can be treated by appropriate medical interventions, the most severe cases especially the elderly who experience underlying medical conditions develop severe illness and increase the mortality rate 8. Older adults with pre-existing medical conditions such as diabetes, asthma, and cardiovascular disease may be more vulnerable to COVID-199. The recognition and discrimination of severe COVID-19, mild infection, and asymptomatic form are clinically vital10. The most important laboratory findings in COVID-19 patients are low concentration of albumin (75.8%), high serum C‐reactive protein (CRP) (58.3%), ESR (41.8%), LDH (57%), and lymphopenia (43%) 11. Lymphopenia was detected in severe COVID-19 patients (85%) and suggested as a severity predictor; the average count of lymphocytes of Intensive Care Unit (ICU) - hospitalized patients was 800 12. Lymphopenia could have occurred in COVID-19 patients via four mechanisms: a) viral attachment to the cell surface receptor ACE2, infect lymphocytes that lead to lymphocyte death 13; b) the possible role of coronavirus in the destruction of lymphoid organs 14; c) induction of lymphocyte apoptosis by the production of TNF-α and IL-615 and d) inhibition of lymphocyte production during metabolic acidosis 16. Although the pathogenesis of COVID-19 remains unclear, lymphopenia was observed in most of the patients 17. Aging and chronic illness lead to endothelial dysfunction that dismounts cell-cell adhesions, promotes endothelial cell death, extravasation that resulted in lymphopenia18. The infection of COVID-19 is diagnosed and confirmed by Real-Time PCR (RT-PCR) and gene sequencing of the blood and lung samples. In the early phase of the disease, positive nasopharyngeal RT-PCR results ranged between 30- 60% 19. In emergency cases, the low sensitivity of RT-PCR misses diagnoses of COVID-19 patients failed receiving appropriate medications and upended outside spreading of COVID-19. In contrast with RT-PCR, chest computed tomography (CT) has sufficient sensitivity for atypical radiographic manifestations of COVID-19 cases who are asymptomatic and/or negative on the initial RT-PCR test 20,21. According to the Chinese reports, chest CT is adequately sensitive (97%) in early detection of COVID- 19 patients compared with RT-PCR22. Bilateral lung involvement was observed in 98% of patients and lobular and subsegmental areas of consolidation were considered as the most typical findings of CT 4. Besides, several COVID-19 cases demonstrated ground-glass opacities (GGO) and pulmonary consolidation with round morphology23. The main CT findings of COVID-19 pneumonia are the shape of GGO, crazy paving pattern, and Consolidation24.
Iran is one of the worst affected countries by the coronavirus and Mazandaran province is considered one of the most impacted areas25. The paucity of evidence on the relationship between lymphopenia, chest CT examination, and mortality rate in COVID-19 patients made us ascertain this possibility. Since Imam Khomeini hospital in Mazandaran was considered as the main referral center for the management of COVID-19 cases, we aim to retrospect and evaluate the lymphopenia in COVID-19 patients and its association with lung involvement.