In December 2019, a large-scale infectious pneumonia of unknown origin broke out in Wuhan, China. Chinese scientists isolated a new coronavirus, SARS-CoV-2, causing the pneumonia on Jan 7, 2020 [1, 2] . And WHO named it Coronavirus Disease 2019 in February 2020 [3] . Since March, justifying the previous data model [4] , COVID-19 has raged across world. Up to Jun 3, 2020, there have been more than 6.4 million diagnosed cases in more than 200 countries, with a mortality rate of about 6% [5] .
The clinical manifestations of COVID-19 range from mild to critical [6] . A lot of observational studies have described the clinical characteristics of patients with COVID-19 in Wuhan [7] [8] [9] [10] , but studies outside Wuhan have rarely been reported. Because of the virus variation, the clinical characteristics of the patients in Wuhan and outside Wuhan maybe different. In this study, we aimed to investigate patients with in Guangzhou to find their clinical characteristics and the risk factors for severe cases. Monitoring these factors can help clinicians identify severe patients early and take subsequent interventions to reduce their illness.
Among the 288 patients, 30 cases were in severe group and only 1 case died by the end of the study. Thus, the severity and mortality were 10.4% and 0.3% respectively. The median age of all patients was 48.5 years (IQR 34. , of which women accounted for 54.5% (Table 1) . 134 (46.5%) patients had comorbidities, of which cardiovascular disease (CVD) (85, 29 .5%) was the most common one, followed by hypertension (84, 29.2%), diabetes (24, 8 .3%) ( Table  1) . 132 patients (45.8%) had a history of exposure to Wuhan 2 weeks before onset ( Table 1 ). The most common symptoms on admission were fever (201, 69.8%) and cough (163, 56.6%), followed by sputum (58, 20.1%), fatigue (43, 14.9%), and myalgia (35, 12.2%) ( Table 1) .
216 (75%) patients had white blood cells (WBC) in normal range and lymphopenia occurred in 91 (31.6%) patients ( Table 2) . Compared with non-severe patients, severe patients had significantly reduced serum hemoglobin, platelet and myoglobin, as well as significantly increased WBC, alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine, creatine kinase, C-reactive protein (CRP), procalcitonin (PCT), brain natriuretic peptide (BNP), and troponin I ( Table 2 ). 31 (10.8%) patients had unilateral pneumonia, and all of them were non-severe patients; 241 (83.7%) patients had bilateral pneumonia, of which 29 (96.7%) were severe patients ( Table 2) . Their chest CTs showed varying degrees of patchy ground-glass opacity, with lung lesion area of severe patients usually larger than that of non-severe patients ( Figure 1 ).
244 (84.7%) patients received antibiotics, and 233 (80.9%) patients received antiviral drugs (oseltamivir / ribavirin; Table 3 ). There was a significant difference in the use of glucocorticoids and vasoactive drugs between non-severe and severe patients (Table 3) . Five patients were treated with continuous renal replacement therapy (CRRT) and four patients were treated with extracorporeal membrane oxygenation (ECMO), and they were all severe patients (Table 3) . 98.9% of the non-severe patients did not take oxygen or took normalflux oxygen, while 43.3% of the severe patients took high-flux oxygen (Table 3) . Eight patients were tracheal intubated and they were all severe patients (Table 3) . Severe patients had a significant increase in use of noninvasive mechanical ventilation than non-severe patients (Table 3) . Compared with non-severe patients, severe patients were more likely to be transferred to the intensive care unit (ICU), and suffer from ARDS, acute kidney injury and acute cardiac injury (Table 3) .
In univariate logistic regression analysis, we found that older patients with hypertension, chronic kidney disease (CKD), and a history of exposure in Wuhan were more likely to develop severe disease (Table 4 ). In addition, fever, shortness of breath, diarrhea, WBC, CRP, lymphocytes, COPD, CVD, hemoglobin, ALT, AST, myoglobin, creatinine, creatine kinase, PCT, BNP and TNI were also related with severe cases ( Table 4 ).
The multivariable logistic regression model was constructed using all variables of significant statistical differences in univariate logistic regression analysis. We found that each 1-year increase in age (OR, 1 
Of the 288 patients in our database, only one case (0.3%) died, while the early mortality rate in Wuhan was as high as 28.3% [3] . And the severity of COVID-19 in Guangzhou is 10.4%, which was far less than that in early Wuhan of 31.7% [11] .
It was interesting to note Guangzhou patients with Wuhan exposure history had a higher risk of becoming severe cases (Table 4 ). Earlier reports reported that some patients had SARS-CoV-2 gene fragments missing, suggesting that their virulence gradually weakened [12] . And an article reported that COVID-19 patients in Zhejiang Province had relatively mild symptoms compared with Wuhan [13] . Later, it was reported that SARS-CoV-2 has genomic diversity. It mutated through replication and may evolve under the pressure of immune surveillance in human body, with its virulence, infectivity and transmission being affected [14] . Therefore, the virulence of SARS-CoV-2 may increase or decrease during transmission, and certain populations in different regions may also have a screening effect on it, resulting in different disease AGING degrees and influencing factors of COVID-19 in different regions.
According to previous reports, older age was an important independent predictor of SARS and MERS mortality [15, 16] . Previous studies have confirmed increased severity and mortality of COVID-19 in old patients [3, 7, 17] . A recent study comparing the clinical characteristics and results of COVID-19 patients of different ages showed that the symptoms of elderly patients were more atypical, with more comorbidities, secondary infection, organ injuries, immunodeficiency and a higher risk of critical illness [18] . Many comorbidities in the elderly such as hypertension, diabetes and CKD were treated with ACE inhibitors and angiotensin II receptor blockers, which would upregulate the ACE2 receptor, thereby increasing the risk of SARS-CoV-2 infection and the risk of disease [19] . In our study cohort, age was also one of the risk factors for severe patients (Table 4) . Therefore, it's very important for old patients to have early diagnosis and treat systemic comorbidities carefully.
SARS-CoV-2 was reported to be detected in stool samples from patients [20] , and a study of a family cluster have reported two COVID-19 patients who had only diarrhea symptom [9] . Besides diarrhea, some patients also had other gastrointestinal symptoms such as vomiting and abdominal pain [21] . Our analysis showed that diarrhea was a risk factor for severe cases (Table 4 ), which suggested that beside of damaging the respiratory system, the virus may also have a certain function on the digestive system. This finding may be related to the expression of SARS-CoV-2 receptor ACE2 in both the epithelial cells of lungs and digestive tract [21, 22] . Given the small number of diarrhea cases showed better status, and some lesions were slightly absorbed than before. Case 2 (severe): Chest CT on Jan 29 (C) showed the texture of both lungs was slightly increased, and both lungs were scattered in patchy shadows, whose edges were blurred. Chest CT on Feb 11 (D) showed the scope of the bilateral lung lesions was enlarged, the density was increased, and the local consolidation and bronchial signs were seen. Chest CT on Mar 4 (E) showed improved status, and both lung lesions were significantly less than before. (11, 3.8%) ( Table 1) , SARS-CoV-2-induced digestive system damage may also be related to other physical factors of these patients, which deserves further study.
Previous studies have reported that COVID-19 nonsurvivors had more neutrophil counts than survivors, which may be related to cytokine storms caused by virus invasion [7, 11] . Our analysis found that elevated WBC and CRP were risk factors for severe cases (Table  4 ). Like neutrophils, WBC and CRP are also indicators of inflammatory status in the body. When they elevated, there may be a cytokine storm caused by virus invasion in the body, which may cause severe inflammation in lungs and other organs, and aggravate the disease. Therefore, paying close attention to changes in WBC, CRP and making timely correction can effectively reduce the number of severe cases and deaths.
In our study, myoglobin, creatine kinase, BNP, and TNI were increased in severe patients compared to non-severe patients (Table 2) , and myoglobin was a risk factor for severe patients, which indicated that COVID-19 may be related to acute cardiac injury. ACE2 is also expressed in heart [23] , and SARS-CoV has been shown in animal models to directly mediate myocardial inflammation and damage by downregulating myocardial ACE2 and lead to poor cardiac prognosis [24] . A meta-analysis involving 4189 patients showed that more severe COVID-19 was associated with increased troponin, creatine kinase, myoglobin, and NT-proBNP [25] . Myoglobin was also included in the COVID-19 severity score table as one of the biomarkers [26] . The severity of COVID-19 may be related to acute cardiac injury, which prompts us to effectively monitor heart condition to prevent AGING COVID-19 patients from myocarditis and avoid poor cardiac prognosis.
Many studies have reported that comorbidities were major risk factors for increasing COVID mortality and poor prognosis [7, 8] , and CKD was one of them. Due to older age, previous comorbidities, impaired immune system, and regular visits to crowded outpatient dialysis centers, CKD patients have increase susceptibility to SARS-COV-2 [27] . On one hand, the above factors have greatly reduced the ability of CKD patients to overcome the virus and may lead to severe disease or even death. On the other hand, SARS-COV-2 can directly damage kidney by combine with ACE2 [28] , and cause kidney inflammation and acute kidney injury [13, 29] , which was consistent with the increase creatinine level of severe patients in our study. AKI could further aggravate CKD as well as worsening the patients' whole conditions, leading patients to develop severe illness.
The study has several limitations. First, the sample size of our study cohort was relatively small including only 288 patients from a single center. Due to the exploratory nature of the study, which was not driven by formal hypotheses, we did not estimate the sample size, but included as many cases as possible. Second, this study lacked laboratory data such as serum cytokines and chemokines, so that we cannot evaluate the inflammation levels and cytokine storms of these patients. Third, this was a retrospective study. The data in this study was only a preliminary assessment of clinical characteristics and risk factors of COVID-19 severe patients. Further researches are still needed.
In conclusion, our research showed that the severity and mortality of COVID-19 in Guangzhou were much lower than those in early Wuhan. The risk factors for severe cases of COVID-19 in Guangzhou included older age, Wuhan exposure history greater than 2 weeks, diarrhea, elevated Myoglobin, elevated WBC and CRP, and CKD. Investigating and monitoring these factors can help clinicians identify patients with poor prognosis at an early stage, and take proactive interventions to benefit patients and reduce severity and mortality. It also provided significant experience and reference for countries around the world to fight against COVID-19.
This single-center, retrospective cohort study was conducted at Guangzhou Eighth People's Hospital (Guangzhou, China), which was the designated hospital to treat patients with COVID-19 in Guangzhou. From [30] . Acute renal injury (ARI) was determined from serum creatinine [31] . Acute cardiac injury (ACI) was determined based on the serum concentration of troponin I (TNI) [11] . The reference ranges of all laboratory inspection indicators were measured in the laboratory of Guangzhou Eighth People's Hospital.
This study reviewed the clinical electronic medical records, nursing records, laboratory tests and radiological findings of 288 adult patients with COVID-19, who were confirmed by nucleic acid testing. And we extracted epidemiology, demographics, clinical manifestations, laboratory data, chest radiography findings, treatment and outcome data for statistical analysis and research.
The purpose of this study was to analyze the risk factors of severe patients by comparing severe group and nonsevere group in terms of their clinical data. Therefore, no formal assumptions were used to facilitate the calculation of the sample size, and we included the largest number of patients who met the inclusion criteria.
We represented continuous variables as median and interquartile range (IQR), and categorical variables as AGING frequency (N) and percentage (%). We assessed differences between severe group and non-severe group using two-sample t test or the Mann-Whitney U test depending on parametric or nonparametric data for continuous variables, and χ 2 test or Fisher's exact test for categorical variables. Univariate and multivariate logistic regression models were used to explore the risk factors for severe cases.
A P value of less than 0.05 was considered statistically significant. All data were statistically analyzed using SPSS software (version 25).
Dr. Feng He, Dr. Qingqing Luo and Dr. Ming Lei contributed equally, they all developed conceptualization and wrote the manuscript under the supervision of Dr. Na Yu, Dr. Liuping Yang and Dr. Jie Cao. Lixin Fan, Xinning Shao, Guanglie Huang, Jun Zeng, Ziwen Zhao, Shuguang Qin, Zhi Yang has participated substantially in the conceptualization and design of this work as well as the writing of the manuscript. All authors have reviewed the final version of the manuscript and have approved it for publication.