This report, to the best of our knowledge, is by far the largest single-center COVID-19 case study of the Wuhan surrounding area in Hubei Province. Our study with these 276 patients confirms that COVID-19 patients in the surrounding area of Wuhan show mainly mild and normal illness with fever and lymphocytopenia as the main clinical features. Older patients (age > 60 years) or those with underlying comorbidities are at higher risk of deteriorating to critical status.
The patients in Zengdu area show mainly mild and normal illness, with a few patients showing severe and critical illness. Wuhan, As the site with the most serious COVID-19 infection in China, many patients did not get timely diagnosis and treatment initially, and medical resources were insufficient to accommodate the sudden burst of patients. As a result, the proportion of severe cases reached 15.0%-30.0% [14, 15], while the rate of severe disease in other regions was 3%-15% [16, 17], similar to 5.1% in this study. This may be because, with the deepening of the understanding of COVID-19 and the formulation of relevant guidelines [18, 19], many patients were diagnosed and treated in a timely manner without deteriorating into severe disease.
The early common symptoms of COVID-19 patients include fever, cough, sputum, and other symptoms of lower respiratory tract infection. As the most common symptom, in general, more than 80% of patients have a fever, but only 38.4% of the patients had a fever at the time of admission, which shows that the fever in many patients was intermittent. It also means a large number of patients with intermittent fever will be set free if instant body temperature readings are the only measure used for screening [2, 20]. The proportion of fever in critically ill patients increases significantly after hospitalization, and most of these new fever cases may be caused by secondary infection, so it is necessary for severe patients to receive antibiotics to prevent secondary infection .
COVID-19 patients over 60 years old were more likely to show deterioration into critical illness. Previous studies on severe acute respiratory syndrome (SARS) and Middle East Respiratory Syndrome (MERS) have confirmed that age was an important predictor of poor prognosis [21, 20], and similar conclusions were obtained for COVID-19 . Data obtained by Nanshan Zhong et al.  and Zhongliang Wang et al.  showed that the age of severe patients was significantly older than that of non-severe patients. Consistent with these findings, among the patients we collected, the median age of severe patients was 65 years, while that of non-severe patients was 50 years. In addition, about 78.6% of the severe patients were more than 60 years old. These studies have shown that older COVID-19 patients have a poor prognosis. However, advanced age often implies more comorbidities and worse lung function, which may also affect the prognosis .
COVID-19 patients with comorbidities were also likely to show deterioration. The studies by Nanshan Zhong et al and Dawei Wang et al.  both showed high proportions of comorbidities in severe patients. A WHO survey reported that people over 60 years of age and those with comorbidities had the highest risk of severe disease . In a recent retrospective study of 25 death cases with COVID-19 , all of the deceased patients have comorbidities, which were considered to be one of the most important risk factors for death. In this study, 85.7% of the severe patients had comorbidities, among which hypertension was the most common. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers are commonly used in many adults with hypertension, diabetes, and chronic kidney disease . Studies have shown that these drugs up-regulate ACE-2 receptors, which are the receptors that SARS-CoV-2 virus uses to enter host cells, which may be one of the reasons why older people with comorbidities are susceptible to infection and deterioration . In addition, COVID-19 damage to the lungs can aggravate some comorbidities, such as chronic obstructive pulmonary disease. Antiviral drugs and glucocorticoids also have limited benefits for patients with comorbidities.
Some early studies had shown that males are more likely to be infected with COVID-19 than females [28, 29]. With more cases, this conclusion has been challenged. Multiple studies have shown that there was no gender-related difference in COVID-19 incidence [20, 14]. Our results indicate that there was no difference in the susceptibility to COVID-19 in males and females. Smoking index and BMI were calculated in this study, but no significant association was found between them and COVID-19 infection; however, this conclusion needs to be further confirmed by more carefully designed studies.
In terms of laboratory tests, 75% of patients had lymphopenia, and more obvious findings were noted in severe patients. The novel coronavirus can induce a cytokine storm and inhibit the generation of lymphocytes [30, 31], so lymphopenia is very common in patients with COVID-19. The low absolute value of lymphocytes can be used as a reference indicator for clinical diagnosis of novel coronavirus infections . Lymphocytes showed a pronounced decline in severe patients than in non-severe patients, indicating that the degree of lymphocyte decline can be used to assess the severity of the disease [23, 32], and that continuous decline of lymphocytes is also one of the indicators of disease deterioration . In addition, we also found that the levels of D-dimer , myohemoglobin, creatine kinase, etc. have increased significantly in severe patients, It seems that they all have the potential to .indicate the severity of the disease [15, 28], but the relevant data were insufficient, we are still unable to draw relevant conclusions.
At present, there is no specific medicine for COVID-19 . All drugs and treatment measures were selected according to the disease condition and the scheme recommended by the guidelines. As most patients were in mild condition and received timely treatment, the cure rate was close to 95%, and only 3.6% of the patients showed deterioration to critical status and were transferred to a hospital. These prognostic data are better than those in the Wuhan area [6, 34]. which is close with the 94% cure rate in other areas of China . The length of hospital stay in this study is slightly longer than that in Wuhan , which may be related to the older and more basic diseases of the patients we included. In addition, the medical resources in Zengdu area are not as tight as in Wuhan, and patients will not have to be discharged as soon as possible, most patients will be hospitalized for some time to recover after a negative virus test.
This study has several limitations. First, since it is a retrospective study with a limited number of patients, some conclusions need to be verified by studies with more rigorous design and larger samples. Second, Zengdu hospital was a community hospital, and most of the critically ill patients had to be transferred to superior hospitals for treatment. we are temporarily unable to get information on the follow-up treatment and complications of these patients. Third, when calculating the incubation period, we excluded the unclear contact date, resulting in fewer patients included, and the potential memory bias will also affect our results.