The current coronavirus disease identified in 2019 , caused by a novel coronavirus, has become a global public health problem [1, 2] . As of May 27, 2020, a total of 5,451,532 cases of COVID-19 have been confirmed globally, including 345,752 deaths [3] . There are many reports suggesting that SARS-CoV-2 RNA can be detected and identified in anal/rectal swabs [4, 5] and stool specimens [6, 7] . In fact, one recent small sample study found that RNA was consistently detected in rectal swabs, even after viral clearance from the upper respiratory tract, indicating extended duration of viral shedding in fecal samples and raising the possibility of fecal-oral transmission of SARS-CoV-2 [5] . Similar results were reported in another study with more cases involved, raising the possibility of prolonged presence of SARS-CoV-2 in stools.
Notably, fecal samples remained positive for SARS-CoV-2 RNA nearly 5 weeks after the viral clearance from the upper respiratory tract in COVID-19 patients [8] .
Considering a high degree of sequence homology between the SARS-CoV-2 and SARS-CoV, angiotensin-converting enzyme II (ACE2) has been identified as the entry receptor of SARS-CoV-2. Since this receptor is highly expressed on the epithelial cells from the ileum and colon [9] , the intestinal tract may be a potential route for SARA-
Patients with cancer are considered to be more susceptible to SARS-CoV-2 [10, 11] .
One patient with rectal cancer was admitted to Zhongnan Hospital of Wuhan University for radical operation. On postoperative day 3, the patient began to develop cough and A c c e p t e d M a n u s c r i p t fever; chest CT revealed radiologic characteristics of viral pneumonia. On postoperative day 7, the patient was confirmed to be infected with SARS-CoV-2.
Although live SARS-CoV-2 had been successfully isolated from the fecal sample of a laboratory confirmed SARS-CoV-2 patient [12] , until now, there has been no direct evidence to prove active SARS-CoV-2 virus replication in the intestinal tract. It remains unknown whether there are pathological changes related to SARS-CoV-2 infection existing in colorectal mucosa in COVID-19 patients. To clarify the above questions, we performed a retrospective study to detect the presence of SARS-CoV-2 virions and determine the pathological changes in rectal tissues of this patient.
The patient's clinical information is described in Supplementary 
Samples of rectal tissues, succus entericus and intestinal mucosa of ileostomy, and rectal mucosa were tested for SARS-CoV-2 nucleic acid using qRT-PCR. The qRT-PCR analyses were performed following a previously described method [13] . The qRT-PCR test kits (BioGerm) were recommended by the Chinese Center for Disease Control A c c e p t e d M a n u s c r i p t and Prevention.
The rectal tissue obtained by resection was soaked in RNAlater solution overnight, the solution was discarded and the tissue was frozen at -80°C. The rectal tissue was cut into 1 mm thick sections and fixed in 2.5% glutaraldehyde and 1% osmium tetroxide in a biosafety cabinet with level 2 protection, and subsequently dehydrated using different ascending concentrations of alcohol (30% to 100%), and immersed and embedded in epoxy resin. Ultrathin sections (80-100 nm) were prepared on formvar-coated copper grids (200 mesh). The virions were observed with a Tecnai G2 20 TWIN electron microscope (FEI company) under 200 kV.
Immunohistochemical staining was performed on formalin-fixed and paraffinembedded tissue sections (4-μm). Sections of rectal tissues were immunostained to evaluate the expression and distribution of the SARS-CoV-2 antigen. Briefly, sections were deparaffinized with xylene and alcohol and subsequently heated in citrate buffer (pH 6.0) for antigen retrieval. After blockage with 3% BSA in PBS for 30 minutes, a rabbit antibody against Rp3 NP protein (kindly provided by Dr. Zhengli Shi, Wuhan Institute of Virology, Chinese Academy of Science [14] ) was incubated with the sections overnight at 4°C. For immunochemistry study, the slides were subsequently Figure 1 .
The patient's clinical information is shown in supplementary Table 1 