DISCUSSION
This systematic review and meta-analysis of observational studies in China used subgroups analyses to objectively reappraise the clinical characteristics of patients with COVID-19-infected pneumonia, including age, sex, chronic medical illness, symptoms, complications, chest radiogram, etc. To our knowledge, this is the first systematic review and meta-analysis of all available trials in China to explore the clinical characteristics of patients with COVID-19-infected pneumonia.
Previous studies have suggested that people of all ages are susceptible to the COVID-19, but older people or those with chronic medical illness are more likely to develop severe pneumonia, ARDS, multiple organ failure, or even death [20-22]. Congruent with previous descriptive reports, we also found that COVID-19-infected pneumonia is common in all age groups. Moreover, our results also revealed that people with cardiovascular disease or endocrine system disease have a higher risk of developing ARDS, multiple organ failure, or even death. However, there were insufficient data from those studies to perform a further meta-analysis. Sex may also contribute to differences in incidence of COVID-19-infected pneumonia. Several observational studies have reported that the incidence of COVID-19-infected pneumonia was higher in men [6-9]. Our results were also consistent with previous report. However, the sex dependence of COVID-19 infections is different from that of severe acute respiratory syndrome (SARS), which as one of the beta-coronavirus family was more than 82% identical to RNA sequence of COVID-19 [23-24]. But our results were limited by the sample size. Future research may shed more light on the issue. In addition, when data on symptoms, complications, and comorbidities were pooled, statistical heterogeneity was detected. The source of heterogeneity may be that the proportion of each type of symptoms, complications, and comorbidities varied widely among the included studies. Recent publications have reported that the clinical characteristics of COVID-19-infected pneumonia mimicked those of SARS [24]. The dominant symptoms include fever and cough. Fatigue and shortness of breath are also common symptoms, whereas gastrointestinal symptoms were rare. Our results were also consistent with previous report. Notably, Guan and colleagues reported that fever occurred in only 43.8% of patients at onset of illness and developed in 87.9% following hospitalization [10]. But Wang and colleagues reported that the most common symptoms at onset of illness were fever (98.6%) [9]. The above differences may confuse readers. In combination with our results, it is considered that fever may be the most common symptom in the course of pneumonia but not in the onset. Huang and colleagues reported that a few patients developed ARDS (29%), acute cardiac injury (12%), and acute kidney injury (7%), and suggested that the heart and kidneys are also important organs for the COVID-19 to attack in addition to the lungs [6]. Consistent with previous studies, our results also exhibited that COVID-19-related heart and kidney injury were also common in severe patients. It seems to further suggest that the lungs may be just a channel for the COVID-19 to attack vital organs in severe patients. But the results also need to be further verified in future studies. In terms of laboratory tests, the included studies-suggested that lymphocyte absolute counts were decreased in most patients, while the white blood cell counts were not detected to be significantly abnormal. This result hinted that COVID-19 might also act on lymphocytes, especially T lymphocytes, as does SARSĀ­CoV [25-26]. However, impaired function of immune system may significantly increase the risk of secondary infection in patients with COVID-19-infected pneumonia. The above may also be the reason why a few patients progressed rapidly with severe bacterial infections, which was eventually followed by multiple organ failure. The included studies showed that abnormalities in chest CT images were detected among all patients on admission. The pooled results revealed that most patients (68%) had bilateral pneumonia. The typical findings of chest imaging showed bilateral ground glass opacity and multiple lobular of consolidation. However, chest imaging of patients usually changes dynamically. In clinical work, we should observe dynamically chest imaging of patients according to their conditions. In addition, it should not be overlooked that some carriers of COVID-19 may have no any clinical symptoms or exhibit typical clinical symptoms but no abnormal changes in chest imaging [27-28]. Some limitations of this systematic review and meta-analysis should be taken into account. First, this paper was limited to 9 observational studies with 1,795 patients. This sample size was not large enough to provide decisional clinical evidence. Second, some observational studies with insufficient information were excluded, which might lead to selection bias. Third, due to incomplete laboratory results provided by included studies, it is not possible to further explore the relationship between biomarkers and COVID-19-infected pneumonia.
In summary, people of all ages are susceptible to COVID-19, but older people or those with chronic medical illness are more likely to develop severe pneumonia, ARDS, multiple organ failure, or even death. Moreover, the incidence of COVID-19-infected pneumonia may be higher in men. The dominant symptoms include fever and cough. Fatigue and shortness of breath are also common symptoms, whereas gastrointestinal symptoms were rare. The heart and kidneys may be also important organs for the COVID-19 to attack in addition to the lungs. Lymphocyte absolute counts in most patients were decreased, and that patients with secondary bacterial infections might appear elevated leucocytes. Most patients may have bilateral imaging abnormalities. The typical findings of chest imaging showed bilateral ground glass opacity and multiple lobular of consolidation.