Dear Editor,
SARS-CoV-2, a novel coronavirus and causing COVID-19, has given rise to a worldwide
pandemic.
1,2
So far, tens of thousands of COVID-19 patients have been clinically cured and discharged,
but multiple COVID-19 cases showed SARS-CoV-2 positive again in discharged patients,
3
which raises an attention for the discharged patients. Also, there is an urgent need
to understand the pathogenesis of SARS-CoV-2 infection. Here, we conducted postmortem
pathologic study in a ready-for-discharge COVID-19 patient who succumbed to sudden
cardiovascular accident. Pathological examination revealed SARS-CoV-2-viruses remaining
in pneumocytes and virus-caused pathological changes in the lungs. Our study provided
new insights into SARS-CoV-2 pathogenesis and might facilitate the improvement of
clinical guideline for virus containment and disease management.
A 78-year-old woman was admitted to hospital on January 27, 2020, due to falling-resulted
trauma. This patient reported that she had been exposed to a COVID-19 patient on January
25th. Since January 29th, the patient showed pneumonia symptoms (Supplementary information,
Fig. S1a). On Feburary 2nd, the patient was confirmed as SARS-CoV-2 positive by nasopharyngeal
swab—PCR test followed by treatment (Supplementary information, Fig. S1a). On Feburary
3rd, chest scan by computerized tomography (CT) showed multiple patchy shadows in
both lungs, implying pulmonary infection (Supplementary information, Fig. S1b). From
Feburary 8th to 10th, three consecutive PCR tests on nasopharyngeal swab samples indicated
SARS-CoV-2 negative (Supplementary information, Fig. S1a). From Feburary 11th to 13th,
the patient’s condition was significantly improved, and CT examination showed absorption
of pulmonary exudation (Supplementary information, Fig. S1a, b). Accordingly, the
patient was ready for discharge. On Feburary 14th, however, this patient fell suddenly
into fatal condition with cardiac arrest, and died unfortunately. Clinical laboratory
test information was summarized in Supplementary information, Table S1, which revealed
that the patient had lymphopenia, a frequent symptom for COVID-19 patients.
Regardless of the negative detection of SARS-CoV-2 virus nucleic acid from nasopharyngeal
swabs, we sought to determine whether there were SARS-CoV-2 viruses remaining in the
patient. We performed digital PCR on tissue sections from the lung, liver, heart,
intestine, and skin, and unexpectedly found positive SARS-CoV-2 virus nucleic acid
only in the lung, but not other tissues (Supplementary information, Fig. S2). Consistently,
electron microscopic observation showed clear coronavirus particles in both bronchiolar
epithelial cells marked by cilia and type II alveolar epithelial cells (type II AE)
featured with lamellar body. The diameters of virus particles were 70–100 nm (Fig. 1a,
b). Furthermore, we conducted immunohistochemical (IHC) staining by using monoclonal
antibody against SARS-CoV-2 nucleocapsid, and confirmed SARS-CoV-2 viruses existed
in the lung tissue (Fig. 1c). Neither coronavirus particles nor SARS-CoV-2 nucleocapsid
were detected in the liver, heart, intestine, skin, and bone marrow. These results
highlight the remaining of SARS-CoV-2 in the lung of discharged COVID-19 patient.
Fig. 1
Pathological observation of the lung tissues.
a Electron microscopic examination on a single pulmonary bronchiolar epithelial cell.
Black arrows in left panel indicate organelle in pulmonary epithelial cell. Red arrows
in right panel label virus particles. Scale bar: 1 μm in left panel and 200 nm in
right panel. b Electron microscopic examination on a single type II alveolar epithelial
cell. Yellow arrow indicates organelle in pulmonary epithelial cell. Red arrows label
virus particles. Scale bar: 200 nm. c Immunohistochemical (IHC) staining of SARS-CoV-2
nucleoprotein (N) in pulmonary tissue with monoclonal anti-nucleoprotein antibody.
The inset represents magnification of the selected area. Dark brown signals indicate
positive staining for SARS-CoV-2 nucleoprotein and nuclei are counterstained with
hematoxylin. Scale bar: 50 μm. d H&E staining shows desquamated and enlarged epithelial
cells. Scale bar: 50 μm. e H&E staining shows exudative monocytes/macrophages in alveoli.
Red arrows show typical macrophages in alveoli. Scale bar: 50 μm. f H&E staining shows
formation of hyaline membranes. Scale bar: 50 μm. g IHC staining indicates lung-infiltrated
immune cells: CD68+ macrophages, CD20+ B cells, and CD8+ T cells. Scale bar: 50 μm.
Histopathological examination of the samples from pulmonary biopsy showed predominant
diffuse alveolar damage, exemplified by the extensive desquamation of proliferative
type II AE, exudative monocytes and macrophages. Some of alveolar walls were partially
lined by low columnar type II AE and covered by the formation of hyaline membranes
in alveolar space. Thickening of alveolar septa with scattered interstitial inflammatory
infiltration and hyaline thrombus in microvessels, but no pulmonary edema was found
(Fig. 1d–f). There were also chronic respiratory disease-associated changes in the
lung tissues. To further delineate the cell types of infiltrated immune cells in alveolar
space and septa, we performed IHC staining and found that they were predominantly
infiltrating CD68+ macrophages, CD20+ B cells, and CD8+ T cells (Fig. 1g). CD4+ T
and CD38+ plasma cells were barely detectable (data not shown).
Pathological features of COVID-19,
4
especially in the pulmonary tissues of mild and recovering patients, remain largely
unknown. In this study, we conducted postmortem study in an aged patient with mild
COVID-19 pneumonia and found pathological changes of the lungs caused by SARS-CoV-2
infection. Histologically, we observed that the patient’s lung was predominated with
diffuse alveolar damages, including disrupt of alveolar septa, proliferation and desquamation
of type II AE, exudation of fibrin, monocytes and macrophages, and formation of hyaline
membrane. These pulmonary pathologic features were consistent with those seen in SARS
and Middle Eastern Respiratory Syndrome (MERS),
5–9
highlighting that the successful methodology in managing SARS and MERS could be referred
to COVID-2019 patients. By using comprehensive means including electron microscopy
and IHC staining, we revealed remaining of SARS-CoV-2 in the lung from the ready-for-discharge
patient, which raises a possibility that nasopharyngeal swab negative result might
not reflect the virus in lung tissue. In addition, our work provided the first pathological
evidence for residual virus in the lung for a patient with virus negative by nasopharyngeal
swab—PCR test for consecutive three times. Therefore, PCR detection of SARS-CoV-2
nucleic acid on broncho-alveolar lavage fluid, extension of quarantine time, and the
timely follow-up medical examination on discharged patients, especially aged ones
with underlying diseases, were strongly recommended for discharged patients.
Supplementary information
Supplementary information