CASE DESCRIPTION

Case 1
A previously healthy 71-year-old man visited the Community Health Center on February 22, presenting 12 days of fever and cough. He underwent an examination of SARS-CoV-2 via real-time reverse transcription polymerase chain reaction (rRT-PCR) and diagnosed as COVID-19. He admitted to the local public medical center and 400 mg of hydroxychloroquine once daily was started. A chest radiograph obtained on day 2 showed mild opacities in the right lower lung, lopinavir/ritonavir 400 mg/100 mg twice daily was added. However, on day 3, oxygen demand increased, so he transferred to the tertiary-care hospital.
At the time of arrival, the patient had no subjective dyspnea under 4 L/min oxygen flow via nasal cannula, but the respiratory rate was over 30 times per minute. Chest radiographs demonstrated rapidly aggravated bilateral infiltration. Routine blood tests found white blood cell (WBC) count at 3.53 × 103/µL, with lymphopenia of 0.4 × 103/µL. C-reactive protein (CRP) and lactic dehydrogenase (LDH) elevated up to 59.7 mg/L and 814 IU/L. Routine chemistry, electrolyte, and blood coagulation tests revealed no abnormalities except mildly elevated aspartate transaminase. The level of interleukin 6 (IL-6) was increased as 101.3 pg/mL. Serial bacterial culture and polymerase chain reaction (PCR) for other respiratory viruses were all negative.
Intubation and mechanical ventilator care were started according to the management of ARDS. Despite the continuous use of lopinavir/ritonavir, hydroxychloroquine and empirical antibiotics, he remained febrile with aggravated oxygenation profiles and chest images. Laboratory test showed further elevation of CRP (172.6 mg/L), IL-6 (208.2 pg/mL).
On day 9, the arterial blood gas analysis showed PaO2/FiO2 of 86, consistent with severe ARDS. Intravenous methylprednisolone (1 mg/kg/day daily) was started. On day 10, convalescent plasma was obtained from a male donor in his 20s who had recovered from COVID-19 for 21 days. He was diagnosed as COVID-19 presenting fever, cough and pneumonia, however, showed complete recovery and didn’t have any symptom at the time of plasma donation. He has met the blood donor eligibility criteria for plasma donation, including age, weight, reasonable-sized antecubital veins. Also, allogeneic donor screening tests, defined by enforcement rules of the Blood Management Act in Korea, were acceptable for transfusion. Donor apheresis was performed with Spectra Optia apheresis system (CMNC software; Spectra Optia IDL Tubing set; Terumo BCT, Lakewood, CO, USA), 500 mL of convalescent plasma was collected. Anti-SARS-CoV-2 IgG antibody in plasma was measured by enzyme-linked immunosorbent assay (ELISA) (Novel Coronavirus COVID-19 IgG ELISA kit; Epitope Diagnostics, San Diego, CA, USA) and optical density (OD) ratio for IgG was 0.586 (cut-off value 0.22). The plasma was divided into two doses and administered to the patient at 12 hours interval. Each dose was given over for 1 hour. No adverse reaction occurred after the administration of convalescent plasma.
The fever subsided, and oxygen demand decreased since day 11. The patient's condition much improved with decreased CRP and IL-6 to normal range (5.7 mg/L and < 1.5 pg/mL, respectively), and on day 18, PaO2/FiO2 increased up to 300 (Fig. 1). A chest X-ray revealed further resolution of both lung infiltrates (Fig. 2). SARS-CoV-2 was quantified by detection of the RNA-dependent RNA polymerase region of the ORF1b gene on rRT-PCR, the value of cycle threshold (Ct) changed from 24.98 on day 10 to 33.96 on day 20 after plasma infusion (Fig. 1). SARS-CoV-2 was negative after day 26. The patient underwent a tracheostomy and currently, is successfully weaned from the mechanical ventilator.
Fig. 1  Case 1, responses to treatment. (A) Timelines of changes in PaO2/FiO2 and CRP during hospitalization. (B) Timelines of detection of the RNA-dependent RNA polymerase region of the ORF1b gene of severe acute respiratory syndrome coronavirus-2 in sputum by real-time reverse transcription polymerase chain reaction; cycle threshold is shown.
CRP = C-reactive protein.
Fig. 2  Chest X-rays of Case 1 taken before and after convalescent plasma infusion. Taken on day 7, just before the convalescent plasma infusion (left). Taken on day 13 shows marked improvement of bilateral infiltrations (right). The images are published under agreement of the patient.

Case 2
A 67-year-old woman with a medical history of hypertension developed fever and myalgia and diagnosed as COVID-19 via SARS-CoV-2 rRT-PCR on March 6. The next day, she was admitted to a local public medical center and received hydroxychloroquine 400 mg once daily and lopinavir/ritonavir 400 mg/100 mg twice daily with empirical antibiotics. However, on day 3, she was transferred to the tertiary-care hospital due to increased oxygen demand and worsening infiltrative shadows in the left lower lung. At that time, her oxygen saturation checked 93% on 4 L/min oxygen flow via nasal cannula with a respiratory rate of 24 times per minute. Routine blood tests showed mild leukocytosis (12.67 × 103/µL) with lymphopenia (0.7 × 103/µL), elevated CRP, IL-6 and LDH. (131.1 mg/L, 474.7 pg/mL, 344 IU/L, respectively) Routine chemistry, electrolyte, and blood coagulation tests showed no abnormalities. Bacterial cultures and the PCR for other respiratory viruses were all negative.
She received high flow oxygen therapy but bilateral infiltration and oxygenation were deteriorated, so intubation and mechanical ventilator care started on day 4. Intravenous methylprednisolone (0.5 mg/kg/day daily) was also added. She had sustained high fever with rapidly increasing CRP (314 mg/L), WBC (21.79 × 103/µL), and persistent lymphopenia (0.5 × 103/µL). PaO2/FiO2 fell to 76, consistent with severe ARDS. After applying for the prone position according to the management of ARDS with the use of steroids, chest images and the oxygen demand began to be improved.
On day 6, convalescent plasma was obtained from a male donor in his 20s who had recovered from COVID-19 for 18 days. He was diagnosed as COVID-19 presenting fever, cough and pneumonia however, showed complete recovery and serial PCRs for SARS-CoV-2 were all negative after hospital discharge. Donor screening and plasma collection were performed as mentioned above in the Case 1. OD ratio for IgG was 0.532 and the plasma was administered to the patient in the same way as Case 1. There was no adverse reaction during the plasma transfusion. Leukocytosis and lymphopenia were immediately recovered after convalescent plasma infusion. On day 9, the density of bilateral infiltration on chest X-ray much improved with increased PaO2/FiO2 to 230. The level of CRP and IL-6 also recovered to the normal range (Figs. 3 and 4). SARS-CoV-2 was quantified by rRT-PCR; the value of Ct changed from 20.51 on day 5 to 36.33 on day 9 after plasma infusion (Fig. 3). The patient is successfully extubated and discharged from the hospital on day 24. SARS-CoV-2 was negative after day 20.
Fig. 3  Case 2, responses to treatment. (A) Timelines of changes in PaO2/FiO2 and CRP during hospitalization. (B) Timelines of detection of the RNA-dependent RNA polymerase region of the ORF1b gene of severe acute respiratory syndrome coronavirus-2 in sputum by real-time reverse transcription polymerase chain reaction; cycle threshold is shown.
CRP = C-reactive protein.
Fig. 4  Chest X-rays of Case 2 taken before and after convalescent plasma infusion. Taken on day 2, before the convalescent plasma infusion (left). Taken on day 6 shows marked improvement of bilateral infiltrations (right). The images are published under agreement of the patient.

Ethics statement
This study was approved by the Institutional Review Board (IRB) of Severance Hospital (IRB No. 4-2020-0076) and with participants' written informed consent. The images are published under agreement of the patients.